Crude methanol complete cascade multi-effect rectification process and rectification device thereof

Abstract

The invention relates to the technical field of crude methanol refining, and discloses a crude methanol complete cascade multi-effect rectification process and a rectification device.The rectification device comprises a pre-rectification tower, a negative pressure tower, a vacuum tower, an atmospheric tower, a medium pressure tower, a pressurizing tower and a high pressure tower which are sequentially connected; the tower top of the vacuum tower is connected with the negative pressure tower reboiler, the tower top of the atmospheric tower is connected with the vacuum tower reboiler, the tower top of the medium pressure tower is connected with the pre-tower reboiler, the tower top of the pressurizing tower is connected with the medium pressure tower reboiler, and the tower top of the high pressure tower is connected with the pressurizing tower reboiler, so that seven-effect cyclic utilization of steam is realized; according to the device, heat closed-loop transfer is completed through six directional tower top pipelines, waste heat of tower bottoms and condensate further preheats feed or upstream material flow, unit consumption of steam can be reduced to 0.20-0.30 t / t refined alcohol, energy consumption is reduced by more than 40%, and the device has the advantages of being compact in structure, stable in operation, high in fusel side line separation efficiency and the like, has economic and environment-friendly values and can reduce emission.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical industry, in particular to a complete cascade multi-effect rectification process for crude methanol and a rectification device thereof. BACKGROUND

[0002] Methanol is an important chemical raw material, which is widely used in chemical industry, energy and fuel cell fields; in the production process of methanol, rectification is a key separation operation for purifying methanol products; the traditional methanol rectification utilizes the technology of heat coupling of pressurized column and atmospheric column to realize energy saving of the rectification system, but a large amount of heat is still wasted in the system, and the energy consumption of the system is still high.

[0003] The existing methanol rectification process usually adopts a three-column process of pre-column, pressurized column and atmospheric column, and utilizes the overhead steam of the pressurized column for heating coupling of the atmospheric column to achieve the purpose of energy saving; however, the overheads of the atmospheric column and the pre-column are cooled by circulating water, resulting in a large amount of heat being wasted, so that the steam consumption of the whole system is relatively high, about 1.2 t of steam per ton of refined methanol.

[0004] Although many rectification energy-saving processes have been developed at present, including five-column three-effect, five-column four-effect, six-column multi-effect and the like, the multiple rectification columns in the above processes are not completely coupled in a cascade manner, and the controllability of the parallel operation process parameters is slightly poor, so that there is still room for further energy saving; for example, the application number 2024218492902 of a six-column eight-effect refining device for crude methanol disclosed by our company discloses a technical solution, which comprises a pre-rectification column, the pre-rectification column is connected with an atmospheric rectification column and a negative pressure rectification column which are arranged in parallel, the atmospheric rectification column and the negative pressure rectification column are connected with a medium pressure rectification column, the medium pressure rectification column is connected with a pressurized rectification column one and a pressurized rectification column two in sequence, the pre-rectification column is connected with a negative pressure column reboiler one through a pre-column overhead take-off pipeline, the atmospheric rectification column is connected with a negative pressure column reboiler two through an atmospheric column overhead take-off pipeline, the medium pressure rectification column is connected with a pre-column reboiler through a medium pressure column overhead take-off pipeline, the pressurized rectification column one is connected with a medium pressure column reboiler and a pressurized column two reboiler through a pressurized column one overhead take-off pipeline one and a pressurized column one overhead take-off pipeline two respectively, and the pressurized rectification column two is connected with an atmospheric column reboiler through a pressurized column two overhead take-off pipeline; the application adopts six-column heat coupling, optimizes the heat exchange network, and improves the energy saving space; the methanol rectification consumption can be reduced from 1.2 t of steam per ton of refined methanol to 0.42-0.50 t of steam per ton of refined methanol, which greatly reduces the operating cost of the enterprise and improves the competitiveness of the enterprise; the methanol rectification consumption of the above application is relatively low, but the multiple rectification columns are not completely coupled in a cascade manner, and the system efficiency still has room for improvement.

[0005] Therefore, it is necessary to provide a new technical solution to solve the above technical problems. SUMMARY

[0006] The application provides a complete crude methanol cascade multi-effect rectification process, which comprises a pre-rectification tower, a negative pressure tower, a reduced pressure tower, an atmospheric pressure tower, a medium pressure tower, a pressurized tower, the pressure of the negative pressure tower, the reduced pressure tower, the atmospheric pressure tower, the medium pressure tower, the pressurized tower, and the high pressure tower gradually increasing in sequence;

[0007] The crude methanol enters the pre-rectification tower for rectification, the gas phase collected from the top of the pre-rectification tower is sent to the atmospheric pressure tower reboiler to provide heat required for rectification of the atmospheric pressure tower, and the liquid phase collected from the pre-rectification tower is sent to the negative pressure tower or the reduced pressure tower;

[0008] When the liquid phase collected from the pre-rectification tower enters the negative pressure tower, the gas phase collected from the top of the negative pressure tower is condensed by the negative pressure tower condenser and then enters the negative pressure tower reflux tank, the liquid phase in the negative pressure tower reflux tank is divided into two streams, one of which is refluxed to the negative pressure tower and the other of which is collected as refined methanol, and the vacuum environment of the negative pressure tower is provided by the negative pressure tower vacuum system; the material in the negative pressure tower is sent to the reduced pressure tower for rectification, the gas phase collected from the top of the reduced pressure tower is sent to the negative pressure tower reboiler to provide heat required for rectification of the negative pressure tower, the gas phase collected from the top of the reduced pressure tower is sent to the reduced pressure tower reflux tank after heat exchange with the negative pressure tower reboiler, the liquid phase in the reduced pressure tower reflux tank is divided into two streams, one of which is refluxed to the reduced pressure tower and the other of which is collected as refined methanol, and the vacuum environment of the reduced pressure tower is provided by the reduced pressure tower vacuum system;

[0009] When the liquid phase collected from the pre-rectification tower enters the reduced pressure tower, the gas phase collected from the top of the reduced pressure tower is sent to the negative pressure tower condenser, is condensed by the negative pressure tower condenser and then enters the negative pressure tower reflux tank, the liquid phase in the negative pressure tower reflux tank is divided into two streams, one of which is refluxed to the reduced pressure tower and the other of which is collected as refined methanol;

[0010] The material in the reduced pressure tower is sent to the atmospheric pressure tower for rectification, the gas phase collected from the top of the atmospheric pressure tower is sent to the reduced pressure tower reboiler to provide heat required for rectification of the reduced pressure tower; the gas phase collected from the top of the atmospheric pressure tower is sent to the atmospheric pressure tower reflux tank after heat exchange with the reduced pressure tower reboiler, the liquid phase in the atmospheric pressure tower reflux tank is divided into two streams, one of which is refluxed to the atmospheric pressure tower and the other of which is collected as refined methanol; and the heat required by the atmospheric pressure tower reboiler is provided by the pre-rectification tower top steam;

[0011] The liquid in the atmospheric pressure tower is sent to the medium pressure tower for further rectification, the gas phase collected from the top of the medium pressure tower is sent to the pre-rectification tower reboiler to provide heat required for rectification of the pre-rectification tower; the gas phase collected from the top of the medium pressure tower is sent to the medium pressure tower reflux tank after heat exchange with the pre-rectification tower reboiler, the liquid phase in the medium pressure tower reflux tank is divided into two streams, one of which is refluxed to the medium pressure tower and the other of which is collected as refined methanol; and the heat required by the medium pressure tower reboiler is provided by the pressurized tower top steam;

[0012] The liquid in the kettle of the medium-pressure column enters the pressurized column for further rectification. The gaseous phase taken from the top of the pressurized column goes to the medium-pressure column reboiler to provide heat required for rectification of the medium-pressure column. The gaseous phase taken from the top of the pressurized column, after heat exchange with the medium-pressure column reboiler, enters the pressurized column reflux tank. The liquid phase in the pressurized column reflux tank is divided into two streams, one of which returns to the pressurized column, and the other is taken out as refined methanol. The pressurized column provides heat required for rectification of the pressurized column in the form of indirect heating by the pressurized column reboiler. The heat required by the pressurized column reboiler is provided by the steam taken from the top of the high-pressure column.

[0013] The liquid in the kettle of the pressurized column enters the high-pressure column for further rectification. The gaseous phase taken from the top of the high-pressure column goes to the pressurized column reboiler to provide heat required for rectification of the pressurized column. The gaseous phase taken from the top of the high-pressure column, after heat exchange with the pressurized column reboiler, enters the high-pressure column reflux tank. The liquid phase in the high-pressure column reflux tank is divided into two streams, one of which returns to the pressurized column, and the other is taken out as refined methanol. The high-pressure column provides heat required for rectification of the high-pressure column in the form of indirect heating by the high-pressure column reboiler. The heat source for the high-pressure column reboiler is steam.

[0014] As a preferred solution, when the low-temperature heat source at the rectification site is over 60℃, a second reboiler is arranged in the kettle of the negative-pressure column, and the low-temperature heat source is used to heat the second reboiler. When the low-temperature heat source at the rectification site is over 70℃, second reboilers are arranged in the kettles of the reduced-pressure column and the negative-pressure column respectively, and the low-temperature heat source is used to heat the second reboilers in sequence. When the low-temperature heat source at the rectification site is over 80℃, second reboilers are arranged in the kettles of the atmospheric column, the reduced-pressure column and the negative-pressure column respectively, and the low-temperature heat source is used to heat the second reboilers in sequence. When the low-temperature heat source at the rectification site is over 100℃, second reboilers are arranged in the kettles of the pre-rectification column, the atmospheric column, the reduced-pressure column and the negative-pressure column respectively, and the low-temperature heat source is used to heat the second reboilers in sequence. When the low-temperature heat source at the rectification site is over 120℃, second reboilers are arranged in the kettles of the medium-pressure column, the pre-rectification column, the atmospheric column, the reduced-pressure column and the negative-pressure column respectively, and the low-temperature heat source is used to heat the second reboilers in sequence.

[0015] As a preferred solution, a vacuum tower is arranged between the pre-distillation tower and the negative pressure tower, and a vacuum tower reboiler is arranged at the lower part of the vacuum tower, and the overhead vapor of the negative pressure tower provides heat for the vacuum tower reboiler.

[0016] As a preferred solution, the logarithmic mean temperature difference between the overhead temperature of the pre-distillation tower and the bottom temperature of the atmospheric tower is 5-12K, the logarithmic mean temperature difference between the overhead temperature of the vacuum tower and the bottom temperature of the negative pressure tower is 5-12K, the logarithmic mean temperature difference between the overhead temperature of the atmospheric tower and the bottom temperature of the vacuum tower is 5-12K, the logarithmic mean temperature difference between the overhead temperature of the medium pressure tower and the bottom temperature of the pre-distillation tower is 5-12K, the logarithmic mean temperature difference between the overhead temperature of the pressurized tower and the bottom temperature of the medium pressure tower is 5-12K, and the logarithmic mean temperature difference between the overhead temperature of the high pressure tower and the bottom temperature of the pressurized tower is 5-12K.

[0017] As a preferred solution, the crude methanol enters the pre-distillation tower after being preheated by the pre-tower preheater one and the pre-tower preheater two, and then enters the pre-distillation tower for rectification, the pre-tower preheater one exchanges heat with the bottom liquid of the pre-distillation tower in counterflow, and the pre-tower preheater two exchanges heat with the medium pressure steam condensate or the low pressure steam condensate.

[0018] As a preferred solution, the bottom liquid of the atmospheric tower enters the medium pressure tower for further rectification after being preheated by the medium pressure tower preheater, and the medium pressure tower preheater exchanges heat with the refined methanol product stream branched from the medium pressure tower reflux tank.

[0019] As a preferred solution, the bottom liquid of the medium pressure tower enters the pressurized tower for further rectification after being preheated by the pressurized tower preheater.

[0020] As a preferred solution, one of the liquid phases in the pressurized tower reflux tank is extracted as refined methanol after exchanging heat with the pressurized tower preheater.

[0021] As a preferred solution, the bottom liquid of the pressurized tower enters the high pressure tower for further rectification after being sequentially heated by the high pressure tower preheater one, the high pressure tower preheater two, and the high pressure tower preheater three.

[0022] As a preferred solution, one of the liquid phases in the high pressure tower reflux tank exchanges heat with the high pressure tower preheater one and is extracted as refined methanol.

[0023] As a preferred solution, the waste water extracted from the bottom of the high pressure tower exchanges heat with the high pressure tower preheater two first and then is extracted.

[0024] As a preferred solution, the medium pressure steam or the low pressure steam heated for the high pressure tower reboiler exchanges heat with the high pressure tower preheater three and the pre-tower preheater two and is extracted as steam condensate.

[0025] The application provides a crude methanol complete cascade multi-effect rectification device, which comprises pre-distillation tower, negative pressure tower, reduced pressure tower, normal pressure tower, medium pressure tower, pressurized tower and high pressure tower which are connected in sequence, the tower kettle of the pre-distillation tower, the negative pressure tower, the reduced pressure tower, the normal pressure tower, the medium pressure tower, the pressurized tower and the high pressure tower are connected with pre-tower reboiler, negative pressure tower reboiler, reduced pressure tower reboiler, normal pressure tower reboiler, medium pressure tower reboiler, pressurized tower reboiler and high pressure tower reboiler respectively, and the heat source of the high pressure tower reboiler is steam; the top of the pre-distillation tower is connected with the normal pressure tower reboiler through a pre-tower top pipeline, the top of the reduced pressure tower is connected with the negative pressure tower reboiler through a reduced pressure tower top pipeline, the top of the normal pressure tower is connected with the reduced pressure tower reboiler through a normal pressure tower top pipeline, the top of the medium pressure tower is connected with the pre-tower reboiler through a medium pressure tower top pipeline, the top of the pressurized tower is connected with the medium pressure tower reboiler through a pressurized tower top pipeline, and the top of the high pressure tower is connected with the pressurized tower reboiler through a high pressure tower top pipeline.

[0026] As a preferred solution, the top of the negative pressure tower is connected with a negative pressure tank reflux tank through a negative pressure tower top pipeline, a negative pressure tower condenser is arranged on the negative pressure tower top pipeline, the reduced pressure tower is connected with the negative pressure tower condenser through a reduced pressure tower top pipeline, the top of the negative pressure tank reflux tank is connected with a negative pressure tower vacuum system, the bottom of the negative pressure tank reflux tank is connected with the middle upper part of the negative pressure tower through a negative pressure tank reflux pipeline, and the bottom of the negative pressure tank reflux tank is also connected with the middle upper part of the reduced pressure tower through a negative pressure tank-reduced pressure tank reflux pipeline, and the negative pressure tank reflux pipeline, the negative pressure tank-reduced pressure tank reflux pipeline and the negative pressure tower refined methanol extraction pipeline are connected.

[0027] As a preferred solution, a vacuum tower is arranged between the pre-distillation tower and the negative pressure tower, the tower kettle of the vacuum tower is connected with a vacuum tower reboiler, and the top of the negative pressure tower is connected with the vacuum tower reboiler through a negative pressure tower top pipeline.

[0028] As a preferred solution, the tower kettle of the pre-distillation tower is connected with the vacuum tower through a pre-tower kettle pipeline, the tower kettle of the vacuum tower is connected with the negative pressure tower through a vacuum tower kettle pipeline, the top of the negative pressure tower is connected with the input end of the vacuum tower reboiler through a negative pressure tower top pipeline, the output end of the vacuum tower reboiler is connected with the negative pressure tank reflux tank, the top of the negative pressure tank reflux tank is connected with a negative pressure tower vacuum system, the bottom of the negative pressure tank reflux tank is connected with the middle upper part of the negative pressure tower through a negative pressure tank reflux pipeline, a negative pressure tank reflux pump is arranged on the negative pressure tank reflux pipeline, and the negative pressure tank reflux pipeline is connected with the negative pressure tower refined methanol extraction pipeline.

[0029] As a preferred solution, the negative pressure tower refined methanol extraction pipeline is connected with a product methanol tank, and a negative pressure tower refined methanol cooler is arranged on the negative pressure tower refined methanol extraction pipeline.

[0030] As a preferred solution, the output end of the atmospheric tower reboiler is connected to the extraction tank through a pre-tower reflux line 1, a pre-tower condenser is provided on the pre-tower reflux line 1, an extraction water line is connected to one side of the extraction tank, a purge gas line is connected to the top of the extraction tank, and the bottom of the extraction tank is connected to the upper part of the pre-distillation tower through a pre-tower reflux line 2, and a pre-tower reflux pump is provided on the pre-tower reflux line 2.

[0031] As a preferred solution, the output end of the negative pressure tower reboiler is connected to the vacuum tower reflux tank through a vacuum tower reflux line 1, the top of the vacuum tower reflux tank is connected to the vacuum tower vacuum system, the bottom of the vacuum tower reflux tank is connected to the top of the vacuum tower through a vacuum tower reflux line 2, a vacuum tower reflux pump is provided on the vacuum tower reflux line 2, and the vacuum tower reflux line 2 is connected to the vacuum tower refined methanol production line.

[0032] As a preferred solution, the vacuum tower refined methanol extraction pipeline is connected to the product methanol tank, and a vacuum tower refined methanol cooler is provided on the vacuum tower refined methanol extraction pipeline.

[0033] As a preferred solution, the output end of the vacuum tower reboiler is connected to the atmospheric tower reflux tank, the bottom of the atmospheric tower reflux tank is connected to the upper part of the atmospheric tower through the atmospheric tower reflux pipeline 2, the atmospheric tower reflux pipeline 2 is provided with an atmospheric tower reflux pump, and the atmospheric tower reflux pipeline 2 is connected to the atmospheric tower refined methanol production pipeline.

[0034] As a preferred solution, the atmospheric tower refined methanol extraction pipeline is connected to the product methanol tank, and an atmospheric tower refined methanol cooler is provided on the atmospheric tower refined methanol extraction pipeline.

[0035] As a preferred solution, the output end of the pre-tower reboiler is connected to the medium-pressure tower reflux tank through medium-pressure tower reflux pipeline 1, the bottom of the medium-pressure tower reflux tank is connected to the medium-pressure tower through medium-pressure tower reflux pipeline 2, a medium-pressure tower reflux pump is provided on the medium-pressure tower reflux pipeline 2, and the medium-pressure tower reflux pipeline 2 is connected to the medium-pressure tower refined methanol production pipeline.

[0036] The atmospheric tower is connected to the medium-pressure tower through the atmospheric tower kettle pipeline. A medium-pressure tower preheater is provided on the atmospheric tower kettle pipeline. The medium-pressure tower refined methanol production pipeline passes through the medium-pressure tower preheater and exchanges heat with the feed of the medium-pressure tower.

[0037] As a preferred solution, the medium-pressure tower refined methanol extraction pipeline is connected to the product methanol tank, and a medium-pressure tower refined methanol cooler is provided on the medium-pressure tower refined methanol extraction pipeline.

[0038] As a preferred solution, the output end of the medium-pressure column reboiler is connected with a pressurized reflux tank through a pressurized reflux pipeline I, the bottom of the pressurized reflux tank is connected with the pressurized column through a pressurized reflux pipeline II, a pressurized reflux pump is arranged on the pressurized reflux pipeline II, and the pressurized reflux pipeline II is connected with a pressurized column refined methanol production pipeline.

[0039] As a preferred solution, the medium-pressure column is connected with the pressurized column through a medium-pressure column kettle pipeline, a pressurized column preheater is arranged on the medium-pressure column kettle pipeline, and a pressurized column refined methanol production pipeline passes through the pressurized column preheater and exchanges heat with pressurized column feed.

[0040] As a preferred solution, the pressurized column refined methanol production pipeline is connected with a product methanol tank, and a pressurized column refined methanol cooler is arranged on the pressurized column refined methanol production pipeline.

[0041] As a preferred solution, the output end of the medium-pressure column reboiler is connected with a high-pressure reflux tank through a high-pressure reflux pipeline I, the bottom of the high-pressure reflux tank is connected with the high-pressure column through a high-pressure reflux pipeline II, a high-pressure reflux pump is arranged on the high-pressure reflux pipeline II, and the high-pressure reflux pipeline II is connected with a high-pressure column refined methanol production pipeline.

[0042] As a preferred solution, the high-pressure column refined methanol production pipeline is connected with a product methanol tank, and a high-pressure column refined methanol cooler is arranged on the high-pressure column refined methanol production pipeline.

[0043] As a preferred solution, one side of the pre-fractionation column is provided with a feed pipeline, and a pre-column preheater I and a pre-column preheater II are arranged on the feed pipeline.

[0044] As a preferred solution, the pre-fractionation column is connected with the negative-pressure column through a pre-column kettle pipeline, and the pre-column kettle pipeline passes through the pre-column preheater I.

[0045] As a preferred solution, the kettle of the pressurized column is connected with the high-pressure column through a pressurized column kettle pipeline, and a high-pressure column preheater I, a high-pressure column preheater II, and a high-pressure column preheater III are arranged on the pressurized column kettle pipeline in sequence.

[0046] As a preferred solution, the high-pressure column refined methanol production pipeline passes through the high-pressure column preheater I.

[0047] As a preferred solution, the kettle of the high-pressure column is provided with a waste water pipeline, and the waste water pipeline passes through the high-pressure column preheater II.

[0048] As a preferred solution, the input end of the high-pressure column reboiler is connected with a steam pipeline, and the output end of the high-pressure column reboiler is connected with a condensate pipeline.

[0049] As a preferred solution, the condensate pipeline passes through high-pressure tower preheater three and pre-tower preheater two in sequence.

[0050] The methanol steam from the top of the high-pressure tower of the present application is used to heat the kettle of the pressurized tower to achieve thermal coupling; the methanol steam from the top of the pressurized tower is used to heat the kettle of the medium-pressure tower to achieve thermal coupling; the methanol steam from the top of the medium-pressure tower is used to heat the kettle of the pre-tower to achieve thermal coupling; the steam from the top of the pre-tower is used to heat the kettle of the atmospheric-pressure tower to achieve thermal coupling; the methanol steam from the top of the atmospheric-pressure tower is used to heat the kettle of the vacuum tower to achieve thermal coupling; the methanol steam from the top of the vacuum tower is used to heat the kettle of the negative-pressure tower to achieve thermal coupling, and the heat closed-loop transfer is completed through six directional tower top pipelines. The waste heat of the kettle liquid and condensate is further used to preheat the feed or upstream logistics, realizing the seven-effect recycling of steam, with significant energy-saving effect; compared with the traditional methanol process, the steam unit consumption can be reduced to 0.20-0.3 0t steam / t refined alcohol, energy consumption is reduced by more than 40%, and it has the advantages of compact structure, stable operation and high side-line separation efficiency of fusel alcohol. It has economic and environmental value and can reduce emissions; for the pre-distillation tower, atmospheric pressure tower, vacuum tower, and negative pressure tower where the kettle temperature is relatively low and the heat source quality requirement is not high, the kettle can partially use external hot water, low-pressure steam and other low-grade heat sources for heating; further, the top steam of the vacuum tower can be switched to be connected to the top condenser of the negative pressure tower. When the cold source is insufficient, the negative pressure tower can be cut out and shut down to perform six-tower operation; when the cold source is sufficient, a vacuum tower can be set before the pre-distillation tower and the negative pressure tower, and the steam from the top of the negative pressure tower can be used to heat the vacuum tower reboiler to realize eight-tower series operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the structure of a seven-tower and six-tower distillation device provided in an embodiment of the present invention;

[0052] Figure 2 This is a seven-tower cascade process flow chart provided by an embodiment of the present invention;

[0053] Figure 3 Schematic diagram of the pressure-temperature ladder provided by an embodiment of the present invention;

[0054] Figure 4 is a thermal cascade curve (GCC) diagram provided by an embodiment of the present invention;

[0055] Figure 5 This is an energy consumption comparison bar chart provided by an embodiment of the present invention;

[0056] Figure 6 Schematic diagram of the structure of an eight-effect distillation device provided by an embodiment of the present invention;

[0057] 1, pre-column; 2, vacuum column; 3, reduced pressure column; 4, atmospheric column; 5, medium pressure column; 6, pressurized column; 7, high pressure column; 8, feed line; 9, pre-column preheater 1; 10, pre-column preheater 2; 11, pre-column column bottom line; 12, vacuum column column bottom line; 13, reduced pressure column column bottom line; 14, atmospheric column column bottom line; 15, medium pressure column preheater; 16, medium pressure column column bottom line; 17, pressurized column preheater; 18, pressurized column column bottom line; 19, high pressure column preheater 1; 20, high pressure column preheater 2; 21, high pressure column preheater 3; 22, side draw line; 23, waste water line; 24, pre-column reboiler; 25, vacuum column reboiler; 26, reduced pressure column reboiler; 27, atmospheric column reboiler; 28, medium pressure column reboiler; 29, pressurized column reboiler; 30, high pressure column reboiler; 31, pre-column overhead line; 32, reduced pressure column overhead line; 33, atmospheric column overhead line; 34, medium pressure column overhead line; 35, pressurized column overhead line; 36, high pressure column overhead line; 37, steam line; 38, condensate line; 39, pre-column reflux line 1; 40, extraction tank; 41, pre-column condenser; 42, extraction water line; 43, purge gas line; 44, pre-column reflux line 2; 45, pre-column reflux pump; 46, vacuum column overhead line; 47, vacuum column reflux tank; 48, vacuum column condenser; 49, vacuum column vacuum system; 50, vacuum column reflux line; 51, vacuum column reflux pump; 52, vacuum column fine methanol take-off line; 53, product methanol tank; 54, vacuum column fine methanol cooler; 55, reduced pressure column reflux line 1; 56, reduced pressure column reflux tank; 57, reduced pressure column vacuum system; 58, reduced pressure column reflux line 2; 59, reduced pressure column reflux pump; 60, reduced pressure column fine methanol take-off line; 61, reduced pressure column fine methanol cooler; 62, atmospheric column reflux line 1; 63, atmospheric column reflux tank; 64, atmospheric column reflux line 2; 65, atmospheric column reflux pump; 66, atmospheric column fine methanol take-off line; 67, atmospheric column fine methanol cooler; 68, medium pressure column reflux line 1; 69, medium pressure column reflux tank; 70, medium pressure column reflux line 2; 71, medium pressure column reflux pump; 72, medium pressure column fine methanol take-off line; 73, medium pressure column fine methanol cooler; 74, pressurized column reflux line 1; 75, pressurized column reflux tank; 76, pressurized column reflux line 2; 77, pressurized column reflux pump; 78, pressurized column fine methanol take-off line; 79, pressurized column fine methanol cooler; 80, high pressure column reflux line 1; 81, high pressure column reflux tank; 82, high pressure column reflux line 2; 83, high pressure column reflux pump; 84, high pressure column fine methanol take-off line; 85, high pressure column fine methanol cooler; 86, pre-column second reboiler; 87, vacuum column; 88, vacuum column column bottom line; 89, vacuum column reboiler; 90, vacuum column overhead take-off line; 91, vacuum column reflux tank; 92, vacuum column condenser; 93, vacuum column vacuum system; 94, vacuum column reflux line; 95, vacuum column reflux pump; 96, vacuum column fine methanol take-off line.97, negative pressure column methanol cooler; 98, vacuum column second reboiler; 99, negative pressure column-decompression column reflux pipeline; 100, negative pressure column second reboiler; 101, decompression column second reboiler; 102, atmospheric column second reboiler; 103, medium pressure column second reboiler. DETAILED DESCRIPTION

[0058] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings, but it should be noted that the specific embodiments described herein are intended to illustrate and explain the present application, and are not intended to limit the present application. Figure 1 The specific embodiments of the present application are described in detail below with reference to the accompanying drawings, but it should be noted that the specific embodiments described herein are intended to illustrate and explain the present application, and are not intended to limit the present application.

[0059] The conventional crude methanol rectification is usually carried out by using three to six towers in parallel or by using incomplete cascade heat coupling, and there is a lack of stepwise pressure matching between the tower top vapor phase and the reboiler, resulting in a large heat exchange temperature difference and a low steam utilization frequency, and the single consumption is maintained at more than 0.42 t of steam per (t of refined alcohol).

[0060] The technical scheme of the present application arranges the towers other than the pre-distillation tower in the ascending order of pressure to form a complete seven-stage heat ladder, and the saturated methanol steam at the tower top of the high-pressure tower 7 at about 1.0 MPa enters the pressurized tower reboiler 29, and the latent heat of the pressurized tower 6 top methanol steam generated after the latent heat is fully absorbed still retains an energy level of about 0.5 MPa, and then drives the reboiling systems of the medium-pressure tower 5, the pre-distillation tower 1, the atmospheric tower 4, the decompression tower 3, and the negative pressure tower 2, and the latent heat of the steam is utilized step by step until the pressure is reduced to 0.03 MPa, so that one steam is used for seven purposes, and the irreversible heat loss is compressed to the minimum temperature difference end.

[0061] The depth matching of the heat coupling between the towers brings a new mass transfer synergistic effect, because the tower top temperature and the next stage tower kettle temperature strictly follow the design window of 5-12K of the logarithmic mean temperature difference, the vapor-liquid phase equilibrium curve on the kettle side is linearly expanded, the theoretical plate number is reduced by about 12%, the internal circulation flow is reduced, the liquid flooding critical load is delayed, the tower internal pressure drop is in a ladder decay, and the overall gas phase rate is maintained in the best interval of 0.25-0.30 ms -1 The low heat transfer temperature difference (the design logarithmic mean temperature difference of the present process is 5-12K) is realized by the cascade coupling of the seven towers with increasing pressure, and the influence logic of the heat transfer temperature difference on the gas-liquid behavior in the tower is as follows:

[0062] Heat transfer reversibility is improved: the low temperature difference makes the energy transfer of the tower top gas phase condensation and the tower kettle liquid phase evaporation closer to the thermodynamic reversible process, reduces the irreversible heat loss, and avoids local overheating or supercooling caused by excessive temperature difference;

[0063] Stable gas-liquid flow rate: Low temperature difference means more accurate matching of pressure gradient in the column, vapor phase rate can be maintained in the optimal interval of 0.25-0.30 m / s, avoiding the entrainment of liquid phase impurities caused by high-speed vapor phase, while inhibiting the risk of liquid flooding of the column tray / packing under low flow rate.

[0064] Optimization of circulation flow: Low temperature difference does not directly reduce the reflux ratio, but improves the mass transfer efficiency through pressure-temperature matching, reducing the circulation flow in the column under the same separation effect, such as reducing the amount of column liquid circulation, thereby reducing the invalid energy consumption.

[0065] Phase equilibrium stability: Low temperature difference makes the vapor-liquid phase equilibrium curve linearly expand, the concentration gradient on each theoretical plate is more uniform, avoiding the separation efficiency fluctuation caused by local concentration mutation, the vacuum system of negative pressure column and vacuum column adopts four-stage coupling regulation: the first stage adjusts the vacuum through fine unloading of frequency conversion fan; the second stage uses spray water to enhance the condensation efficiency of air cooler in summer; the third stage recovers methanol vapor through frozen water pre-condensation, reducing the gas amount entering the subsequent link; the fourth stage uses a water ring pump with a methanol recovery unit to deep vacuum, the vacuum fluctuation is locked within ±0.8 kPa; the interlocking valve group adjusts the reflux valve position of the column top in real time, the differential pressure-liquid level double variable self-tuning avoids the common "negative pressure deviation-high pressure backflow" accident in multi-column system, ensuring long-term stable operation.

[0066] In the fine separation of fusel alcohol and formaldehyde and other trace components, this process uses high-pressure column side methanol purity control, light components are controlled by controlling the pre-distillation column reflux, and heavy components are controlled by controlling the high-pressure column side sampling amount, to control the fusel alcohol content below 400 ppm; at the same time, the high-pressure column 7 column waste water is recovered by two-stage preheater to recover more than 30% of the sensible heat, and the methanol concentration at the discharge port is less than 150 mg / L -1 , which saves a lot of cooling and aeration load for downstream biochemical treatment.

[0067] The present application is verified by 4.4×10 4 kgh -1 The steam consumption is stable at 0.249 t steam / (t of refined alcohol), and the power consumption is 21.6 kWh(t of refined alcohol) -1 ; the comprehensive energy utilization rate is improved to 67%, saving 1.8×10 4 ta -1 of standard coal per year compared with the same scale device in China, and reducing CO2 emission by 4.7×10 4 t per year.

[0068] Example 1:

[0069] The embodiment provides a specific application of a complete crude methanol cascade multi-effect rectification process, including a pre-rectification tower 1, a negative pressure tower 2, a reduced pressure tower 3, an atmospheric pressure tower 4, a medium pressure tower 5, a pressurized tower 6 and a high pressure tower 7 connected in sequence, the negative pressure tower 2, the reduced pressure tower 3, the atmospheric pressure tower 4, the medium pressure tower 5, the pressurized tower 6 and the high pressure tower 7 are arranged in a step-by-step increasing pressure mode, and a pressure-temperature ladder diagram of each tower is shown in the figure Figure 3 The logarithmic mean temperature difference between the tower top temperature of the pre-rectification tower 1 and the tank temperature of the atmospheric pressure tower 4 is 5-12K, the logarithmic mean temperature difference between the tower top temperature of the reduced pressure tower 3 and the tank temperature of the negative pressure tower 2 is 5-12K, the logarithmic mean temperature difference between the tower top temperature of the atmospheric pressure tower 4 and the tank temperature of the reduced pressure tower 3 is 5-12K, the logarithmic mean temperature difference between the tower top temperature of the medium pressure tower 5 and the tank temperature of the pre-rectification tower 1 is 5-12K, the logarithmic mean temperature difference between the tower top temperature of the pressurized tower 6 and the tank temperature of the medium pressure tower 5 is 5-12K, and the logarithmic mean temperature difference between the tower top temperature of the high pressure tower 7 and the tank temperature of the pressurized tower 6 is 5-12K; more preferably, the logarithmic mean temperature difference between the tower top temperature of the medium pressure tower 5 and the tank temperature of the pre-rectification tower 1 is 5-12K, and the logarithmic mean temperature difference between the tower top temperature of the medium pressure tower 5 and the tank temperature of the pre-rectification tower 1 is 5-12K.

[0070] The embodiment provides a specific application of a complete crude methanol cascade multi-effect rectification process, including a pre-rectification tower 1, a negative pressure tower 2, a reduced pressure tower 3, an atmospheric pressure tower 4, a medium pressure tower 5, a pressurized tower 6 and a high pressure tower 7 connected in sequence, the negative pressure tower 2, the reduced pressure tower 3, the atmospheric pressure tower 4, the medium pressure tower 5, the pressurized tower 6 and the high pressure tower 7 are arranged in a step-by-step increasing pressure mode, and a pressure-temperature ladder diagram of each tower is shown in the figure

[0071] The crude methanol enters a pre-tower pre-heater one 9 and a pre-tower pre-heater two 10 for pre-heating, the crude methanol is pre-heated to about 80 DEG C, the pre-heated crude methanol enters the pre-rectification tower 1 for rectification, the pre-rectification tower 1 has a tower top pressure of 170 KPa, a tower top temperature of 81 DEG C and a tank temperature of 83 DEG C; gas phase collected from the top of the pre-rectification tower 1 is used to provide heat required for rectification of the atmospheric pressure tower 4 through the atmospheric pressure tower reboiler 27, and after being cooled through the pre-tower condenser 41, the gas phase enters an extraction tank 40, and after extraction in the extraction tank 40, the water phase is returned to the pre-rectification tower 1, and the non-condensed gas is discharged; the pre-tower pre-heater one 9 and the pre-rectification tower 1 exchange heat countercurrently, that is, the liquid phase collected from the tank of the pre-rectification tower 1 is cooled through the pre-tower pre-heater one 9 and then enters the negative pressure tower 2 or the reduced pressure tower 3.

[0072] The liquid phase taken out from the pre-distillation column 1 enters the negative pressure column 2, the pressure at the top of the negative pressure column 2 is 40 KPa, the temperature at the top of the negative pressure column 2 is 43℃, the temperature at the bottom of the negative pressure column 2 is 50℃, the gas phase taken out from the top of the negative pressure column 2 enters the negative pressure reflux tank 47 after being condensed by the negative pressure column condenser 48, the liquid phase in the negative pressure reflux tank 47 is divided into two streams, one of which is returned to the negative pressure column 2, and the other is taken out as refined methanol, preferably, the refined methanol is stored in the product methanol tank 53 after being cooled by the negative pressure column refined methanol cooler 54, the heat required by the negative pressure column reboiler 25 is provided by the methanol steam at the top of the decompression column 3, the vacuum environment of the negative pressure column 2 is provided by the negative pressure column vacuum system 49, the material at the bottom of the negative pressure column 2 enters the decompression column 3 for rectification, the pressure at the top of the decompression column 3 is 70 KPa, the temperature at the top of the decompression column 3 is 55℃, the temperature at the bottom of the decompression column 3 is 63℃, the gas phase taken out from the top of the decompression column 3 enters the negative pressure column reboiler 25 to provide the heat required for rectification of the negative pressure column 2, the material enters the decompression reflux tank 56 after being exchanged by the negative pressure column reboiler 25, the liquid phase in the decompression reflux tank 56 is divided into two streams, one of which is returned to the decompression column 3, and the other is taken out as refined methanol, preferably, the refined methanol is stored in the product methanol tank 53 after being cooled by the decompression column refined methanol cooler 61, the heat required by the decompression column reboiler 26 is provided by the methanol steam at the top of the normal pressure column 4, the vacuum environment of the decompression column 3 is provided by the decompression column vacuum system 57;

[0073] The decompression column top steam can be switched to be connected with the negative pressure column top condenser, and the negative pressure column 2 is shut down in the case of insufficient cooling source of the negative pressure column top condenser to perform six-column operation, that is, the liquid phase taken out from the pre-distillation column 1 enters the decompression column 3, the gas phase taken out from the top of the decompression column 3 enters the negative pressure column condenser 48 after being condensed, and then enters the negative pressure reflux tank 47, the liquid phase in the negative pressure reflux tank 47 is divided into two streams, one of which is returned to the decompression column 3, and the other is taken out as refined methanol;

[0074] The material at the bottom of the decompression column 3 enters the normal pressure column 4 for rectification, the pressure at the top of the normal pressure column 4 is 115 KPa, the temperature at the top of the normal pressure column 4 is 68℃, the temperature at the bottom of the normal pressure column 4 is 76℃, the gas phase taken out from the top of the normal pressure column 4 enters the decompression column reboiler 26 to provide the heat required for rectification of the decompression column 3, the material enters the normal pressure reflux tank 63 after being exchanged by the decompression column reboiler 26, the liquid phase in the normal pressure reflux tank 63 is divided into two streams, one of which is returned to the normal pressure column 4, and the other is taken out as refined methanol, preferably, the refined methanol is stored in the product methanol tank 53 after being cooled by the normal pressure column refined methanol cooler 67, the heat required by the normal pressure column reboiler 27 is provided by the pre-column distillation column 1 top steam;

[0075] The column bottom liquid of the atmospheric column 4 is preheated by the medium pressure column preheater 15 and then enters the medium pressure column 5 for further rectification. The medium pressure column 5 has a column top pressure of 300 KPa, a column top temperature of 95°C and a column bottom temperature of 109°C. The gaseous phase taken from the column top of the medium pressure column 5 enters the pre-column reboiler 24 to provide the heat required for rectification of the pre-distillation column 1. After heat exchange, the gaseous phase enters the medium pressure column reflux tank 69. The liquid phase in the medium pressure column reflux tank 69 is divided into two streams. One stream is refluxed to the medium pressure column 5. The other stream is preheated by the medium pressure column preheater 15 and then taken as refined methanol. Preferably, the refined methanol is cooled by the medium pressure column refined methanol cooler 73 and then stored in the product methanol tank 53. The medium pressure column 5 is indirectly heated by the medium pressure column reboiler 28 to provide the heat required for rectification of the medium pressure column 5. The heat source of the medium pressure column reboiler 28 is the gaseous phase taken from the column top of the pressurized column 6.

[0076] The column bottom liquid of the medium pressure column 5 is preheated by the pressurized column preheater 17 and then enters the pressurized column 6 for further rectification. The pressurized column 6 has a column top pressure of 550 KPa, a column top temperature of 115°C and a column bottom temperature of 132°C. The gaseous phase taken from the column top of the pressurized column 6 enters the medium pressure column reboiler 28 to provide the heat required for rectification of the medium pressure column 5. After heat exchange, the gaseous phase enters the pressurized column reflux tank 75. The liquid phase in the pressurized column reflux tank 75 is divided into two streams. One stream is refluxed to the pressurized column 6. The other stream is preheated by the pressurized column preheater 17 and then taken as refined methanol. Preferably, the refined methanol is cooled by the pressurized column refined methanol cooler 79 and then stored in the product methanol tank 53. The pressurized column 6 is indirectly heated by the pressurized column reboiler 29 to provide the heat required for rectification of the pressurized column 6. The heat source of the pressurized column reboiler 29 is the gaseous phase taken from the column top of the high pressure column 7.

[0077] The column bottom liquid of the pressurized column 6 is sequentially preheated by the high pressure column preheater one 19, the high pressure column preheater two 20 and the high pressure column preheater three 21 and then enters the high pressure column 7 for further rectification. The high pressure column 7 has a column top pressure of 1050 KPa, a column top temperature of 139°C and a column bottom temperature of 182°C. The gaseous phase taken from the column top of the high pressure column 7 enters the pressurized column reboiler 29 to provide the heat required for rectification of the pressurized column 6. After condensation, the gaseous phase enters the high pressure column reflux tank 81. The liquid phase in the high pressure column reflux tank 81 is divided into two streams. One stream is refluxed to the pressurized column 6. The other stream is preheated by the high pressure column preheater one 19 and then taken as refined methanol. Preferably, the refined methanol is cooled by the pressurized column refined methanol cooler 85 and then stored in the product methanol tank 53. The high pressure column 7 is indirectly heated by the high pressure column reboiler 30 to provide the heat required for rectification of the high pressure column 7. The heat source of the high pressure column reboiler 30 is medium pressure steam or low pressure steam. The pre-column preheater two 10 and the high pressure column preheater three 21 exchange heat with the steam condensate. That is, after heat supply, the medium pressure steam or low pressure steam exchanges heat with the high pressure column preheater three 21 and the pre-column preheater two 10 and is then taken as steam condensate.

[0078] Example 2:

[0079] like Figure 6 As shown, the difference between this embodiment and Example 2 is that, when the cold source of the negative pressure tower top condenser is sufficient, such as when the temperature of the cold source is -10 degrees Celsius, a vacuum tower is set between the pre-distillation tower 1 and the negative pressure tower 2, and a vacuum tower reboiler is set at the lower part of the vacuum tower. The steam from the negative pressure tower top is used to heat the vacuum tower reboiler, thereby realizing eight-tower series operation; when the vacuum tower is set, the tower kettle of the pre-distillation tower 1 is connected to the vacuum tower, and the tower kettle of the vacuum tower is connected to the negative pressure tower 2.

[0080] Example 3:

[0081] The present embodiment provides a complete cascade multi-effect distillation device for crude methanol, comprising a pre-distillation tower 1, a negative pressure tower (negative pressure distillation tower) 2, a vacuum tower (vacuum distillation tower) 3, an atmospheric pressure tower (atmospheric pressure distillation tower) 4, a medium-pressure tower (medium-pressure distillation tower) 5, a pressurized tower (pressurized distillation tower) 6, and a high-pressure tower (high-pressure distillation tower) 7 connected in sequence. Preferably, the top pressure of the pre-distillation tower 1 is 120kPa-180kPa, the top pressure of the negative pressure tower 2 is 20kPa-60kPa, the top pressure of the vacuum tower 3 is 50kPa-90kPa, the top pressure of the atmospheric pressure tower 4 is 90kPa-140kPa, the top pressure of the medium-pressure tower 5 is 200kPa-450kPa, the top pressure of the pressurized tower 6 is 400kPa-700kPa, and the top pressure of the high-pressure tower 7 is 600kPa-1200kPa.

[0082] A feed pipeline 8 is provided on one side of the pre-distillation tower 1, and a pre-tower preheater 9 and a pre-tower preheater 10 are sequentially provided on the feed pipeline 8, which are used to preheat the crude methanol material entering the pre-distillation tower 1 to improve the stability of the distillation; preferably, a normal temperature negative pressure flash tank is provided in front of the preheater 9 to flash out a portion of the CO2 in the crude methanol, which is conducive to the coupling of the top gas of the pre-distillation tower 1 to the atmospheric pressure tower 4;

[0083] The bottom of the pre-distillation column 1 is connected with the negative pressure column 2 through a pre-column column bottom pipeline 11, and connected with the reduced pressure column 3 through the pre-column column bottom pipeline 11 and a negative pressure column column bottom pipeline 12, and corresponding valves are arranged on the pre-column column bottom pipeline 11 and the negative pressure column column bottom pipeline 12, for controlling the column bottom liquid of the pre-distillation column 1 to flow into the negative pressure column 2 or the reduced pressure column 3; the pre-column column bottom pipeline 11 passes through a pre-column pre-heater one 9, i.e. the pre-column column bottom pipeline 11 is connected with the input end and the output end of the pre-column pre-heater one 9, and the heat of the column bottom of the pre-distillation column 1 is used to heat the pre-column pre-heater one 9; the column bottom of the negative pressure column 2 is connected with the reduced pressure column 3 through a negative pressure column column bottom pipeline 12, the column bottom of the reduced pressure column 3 is connected with the normal pressure column 4 through a reduced pressure column column bottom pipeline 13, the column bottom of the normal pressure column 4 is connected with the medium pressure column 5 through a normal pressure column column bottom pipeline 14, preferably, a medium pressure column pre-heater 15 is arranged on the normal pressure column column bottom pipeline 14, and the material of the column bottom of the normal pressure column 4 is pre-heated through the medium pressure column pre-heater 15 and then enters the medium pressure column 5; the column bottom of the medium pressure column 5 is connected with the pressurized column 6 through a medium pressure column column bottom pipeline 16, preferably, a pressurized column pre-heater 17 is arranged on the medium pressure column column bottom pipeline 16, and the material of the column bottom of the medium pressure column 5 is pre-heated through the pressurized column pre-heater 17 and then enters the pressurized column 6; the column bottom of the pressurized column 6 is connected with the high pressure column 7 through a pressurized column column bottom pipeline 18, preferably, a high pressure column pre-heater one 19, a high pressure column pre-heater two 20 and a high pressure column pre-heater three 21 are arranged on the pressurized column column bottom pipeline 18 in sequence, and the material of the column bottom of the pressurized column 6 is heated through the high pressure column pre-heater one 19, the high pressure column pre-heater two 20 and the high pressure column pre-heater three 21 in sequence and then enters the high pressure column 7; one side of the high pressure column 7 is provided with a side taking pipeline 22 for taking out fusel alcohol, and the control target of the side taking pipeline 22 is that the compliance rate of the ethanol at the top of the high pressure column 7 is higher, and the content of methanol in the side taking is controlled to be less than 20%; the column bottom of the high pressure column 7 is provided with a waste water pipeline 23 for taking out waste water, and the waste water pipeline 23 passes through the high pressure column pre-heater two 20, i.e. the waste water pipeline 23 is connected with the input end and the output end of the high pressure column pre-heater two 20, the waste water taken out from the column bottom of the high pressure column 7 is used to heat the high pressure column pre-heater two 20, and the heat-exchanged waste water is taken out.

[0084] The kettle of the pre-distillation column 1, the negative pressure column 2, the reduced pressure column 3, the normal pressure column 4, the medium pressure column 5, the pressurized column 6, and the high pressure column 7 is respectively connected with the pre-column reboiler 24, the negative pressure column reboiler 25, the reduced pressure column reboiler 26, the normal pressure column reboiler 27, the medium pressure column reboiler 28, the pressurized column reboiler 29, and the high pressure column reboiler 30, and the gas phase at the top of each column provides heat for the reboiler of the next low pressure column in turn along the material flow, forming a complete seven-effect heat coupling. Specifically, the overhead vapor of the pre-distillation column 1 provides heat for the normal pressure column reboiler 27, i.e. the overhead vapor of the pre-distillation column 1 heats the kettle of the normal pressure column 4 to realize heat coupling; the overhead vapor of the reduced pressure column 3 provides heat for the negative pressure column reboiler 25, i.e. the overhead methanol vapor of the reduced pressure column 3 heats the kettle of the negative pressure column 2 to realize heat coupling; the overhead vapor of the normal pressure column 4 provides heat for the reduced pressure column reboiler 26, i.e. the overhead methanol vapor of the normal pressure column 4 heats the kettle of the reduced pressure column 3 to realize heat coupling; the overhead vapor of the medium pressure column 5 provides heat for the pre-column reboiler 24, i.e. the overhead methanol vapor of the medium pressure column 5 heats the kettle of the pre-distillation column 1 to realize heat coupling; the overhead vapor of the pressurized column 6 provides heat for the medium pressure column reboiler 28, i.e. the overhead methanol vapor of the pressurized column 6 heats the kettle of the medium pressure column 5 to realize heat coupling; the overhead vapor of the high pressure column 7 provides heat for the pressurized column reboiler 29, i.e. the overhead methanol vapor of the high pressure column 7 heats the kettle of the pressurized column 6 to realize heat coupling; more specifically: the top of the pre-distillation column 1 is connected with the normal pressure column reboiler 27 through a pre-column overhead pipeline 31 to provide heat required for the rectification of the normal pressure column 4; the top of the reduced pressure column 3 is connected with the negative pressure column reboiler 25 through a reduced pressure column overhead pipeline 32 to provide heat required for the rectification of the negative pressure column 2; the top of the reduced pressure column 3 is also connected with the negative pressure column condenser 48 at the top of the negative pressure column 2 through the reduced pressure column overhead pipeline 32; the top of the normal pressure column 4 is connected with the reduced pressure column reboiler 26 through a normal pressure column overhead pipeline 33 to provide heat required for the rectification of the reduced pressure column 3; the top of the medium pressure column 5 is connected with the pre-column reboiler 24 through a medium pressure column overhead pipeline 34 to provide heat required for the rectification of the pre-distillation column 1; the top of the pressurized column 6 is connected with the medium pressure column reboiler 28 through a pressurized column overhead pipeline 35 to provide heat required for the rectification of the medium pressure column 5; the top of the high pressure column 7 is connected with the pressurized column reboiler 29 through a high pressure column overhead pipeline 36 to provide heat required for the rectification of the pressurized column 6; Table 1 below is a schematic diagram of the energy-material coupling network between the columns;

[0085]

[0086] Table 1 Energy-material coupling network between columns

[0087] The high-pressure column reboiler 30 is heated by steam, specifically, the input end of the high-pressure column reboiler 30 is connected with the steam pipeline 37, and the output end of the high-pressure column reboiler 30 is connected with the condensate pipeline 38; in order to further improve the utilization rate of steam, the condensate pipeline 38 passes through the high-pressure column preheater three 21 and the pre-column preheater two 10 in sequence, that is, the condensate pipeline 38 is connected with the input end and the output end of the high-pressure column preheater three 21, and the condensate pipeline 38 is connected with the input end and the output end of the pre-column preheater two 10; after the steam condensate provides heat for the high-pressure column preheater three 21 and the pre-column preheater two 10, the steam condensate is taken out as condensate.

[0088] More specifically: the pressure gradient of the embodiment is: pre-fractionating column 1 (170 / 180) - negative pressure column 2 (40 / 50) - reduced pressure column 3 (70 / 75) - normal pressure column 4 (115 / 121) - medium pressure column 5 (300 / 340) - pressurized column 6 (550 / 570) - high pressure column 7 (1050 / 1076); the pre-fractionating column 1 (170 / 180) refers to the operating pressure range of the pre-fractionating column 1 being 170 kPa-180 kPa, and the like, which will not be repeated here; the temperature coupling relationship is: high pressure column 7 (139 / 182) - pressurized column 6 (115 / 132) - medium pressure column 5 (95 / 109) - pre-fractionating column 1 (81 / 83) - normal pressure column 4 (68 / 76) - reduced pressure column 3 (55 / 63) - negative pressure column 2 (43 / 50); the high pressure column 7 (139 / 182) refers to the operating temperature range of the high pressure column being 139℃-182℃, and the like, which will not be repeated here; the above gradient can ensure that the high-temperature column top steam can drive the low-temperature column bottom heat transfer.

[0089] The gas phase pipelines between the columns are independent of each other, the column bottom liquid phase is transported by a mechanical pump, and the pressure of each column is determined by the heating and cooling medium temperature of each column and the heat exchange effect of the coupling reboiler; through reasonable design of the reboiler and adjustment of the effective heating area in the operation process, the pressure difference of each column can be effectively controlled; the above content belongs to the conventional prior art, and the applicant will not make specific elaboration; the negative pressure column 2 and the reduced pressure column 3 are respectively vacuumized by the negative pressure column vacuum system 49 and the reduced pressure column vacuum system 57, so that the negative pressure column 2 and the reduced pressure column 3 are maintained in a low pressure state and form a stable pressure difference with the upstream column;

[0090] The vacuum degree affects the heat transfer temperature difference, and thus the heat exchanger efficiency, the weather temperature and the humidity all affect the vacuum degree of the negative pressure column 2 and the reduced pressure column 3; the pressure control scheme of the negative pressure column 2 and the reduced pressure column 3 is as follows:

[0091] First-level regulation: when the pressure of the reduced pressure column 3 and / or the negative pressure column 2 increases, the frequency conversion fan of the reduced pressure column condenser of the reduced pressure column vacuum system 57 and / or the frequency conversion fan and the circulating water inlet and outlet temperature monitoring adjustment of the negative pressure column condenser of the negative pressure column vacuum system 49 need to be adjusted;

[0092] Secondary regulation mode: when primary regulation is insufficient to maintain pressure, secondary regulation mode is started, air cooling in summer is not easy to control, water needs to be sprayed, and the air cooler becomes a wet evaporation cooling mode;

[0093] Tertiary regulation mode: after primary and secondary regulation, the pressure in the tower is still rising, then multiple vacuum pumps are connected in parallel, and the air volume of the vacuum pump is increased to maintain the vacuum degree of the vacuum tower 2 and the vacuum tower 3;

[0094] Four regulation mode: a heat exchanger using chilled water as a condensing medium is added before the vacuum pump to condense the steam that cannot be condensed by circulating water, reduce the amount of gas entering the vacuum pump, and improve the effective air extraction efficiency of the vacuum pump.

[0095] Figure 4 The GCC diagram of the present application is a heat energy cascade curve, the dashed line represents the cold required by the hot stream, and the straight line represents the heat required by the cold stream. The schematic diagram shows that the heat provided by the tower top and the heat required by the tower bottom are matched and can be coupled.

[0096] The present embodiment uses the principle of multi-effect rectification, adjusts the operating pressure of each tower, generates a temperature gradient in each tower, uses the tower top steam of the rectification tower with higher temperature as the heat source of the tower bottom of the rectification tower with lower temperature, achieves multiple coupling of energy, greatly reduces the steam energy consumption of the system, realizes complete cascade coupling of multiple towers, increases the steam utilization efficiency, and will have greater energy saving and carbon reduction benefits. The single consumption of methanol rectification in the present embodiment can be reduced from 1.2 t of steam / t of rectified alcohol to 0.20-0.30 t of steam / t of rectified alcohol, which can save more than 70% of energy compared with the traditional double-tower thermal coupling process, greatly reduces the operating cost of enterprises, significantly reduces carbon emissions, and improves the competitiveness of enterprises.

[0097] Example Four:

[0098] The difference between this embodiment and embodiment three is that a vacuum tower 87 is arranged between the pre-distillation tower 1 and the negative pressure tower 2, the tower kettle of the pre-distillation tower 1 is connected with the vacuum tower 87 through a pre-tower kettle pipeline 11, the pre-tower kettle pipeline 11 passes through a pre-tower pre-heater 9; the tower kettle of the vacuum tower 87 is connected with the negative pressure tower 2 through a vacuum tower kettle pipeline 88, a vacuum tower reboiler 89 is arranged at the lower part of the vacuum tower 87, the top of the vacuum tower 87 is connected with a vacuum tower top take-out pipeline 90, the vacuum tower top take-out pipeline 90 is provided with a vacuum tower condenser 92, a vacuum tower vacuum system 93 is arranged at the top of the vacuum tower 87, the vacuum tower 87 is connected with a vacuum tower refined methanol take-out pipeline 96 through a vacuum tower reflux pipeline 94, the vacuum tower reflux pipeline 94 is provided with a vacuum tower reflux pump 95, and the vacuum tower reflux pipeline 94 is also connected with the vacuum tower refined methanol take-out pipeline 96; the top of the negative pressure tower 2 is connected with the vacuum tower reboiler 89 through a negative pressure tower top pipeline 46, and the output end of the vacuum tower reboiler 89 is connected with a negative pressure tower reflux tank 47.

[0099] Preferably, the vacuum tower refined methanol take-out pipeline 96 is connected with a product methanol tank 53, and the vacuum tower refined methanol take-out pipeline 96 is provided with a negative pressure tower refined methanol cooler 97; the refined methanol taken out is stored in the product methanol tank 53 after being cooled by the vacuum tower refined methanol cooler 97; in this embodiment, the negative pressure tower 2 top steam is used to heat the vacuum tower reboiler 89, so that eight towers are operated in series.

[0100] Preferably, the tower kettle of the vacuum tower 87 can be additionally provided with a second vacuum tower reboiler 98 according to the actual coupling condition and the on-site heat source condition, so as to use the external low-temperature waste heat to heat partially, thereby further reducing the steam consumption while maintaining the product quality.

[0101] Embodiment five:

[0102] In this embodiment, on the basis of embodiment three, the reflux and / or refined methanol take-out of each tower are specifically described, and specifically:

[0103] The output end of the atmospheric column reboiler 27 is connected with an extraction tank 40 through a pre-reflux pipeline I 39 provided with a pre-column condenser 41, one side of the extraction tank 40 is connected with an extraction water pipeline 42, the top of the extraction tank 40 is connected with a vent gas pipeline 43, the bottom of the extraction tank 40 is connected with the upper part of the pre-distillation column 1 through a pre-reflux pipeline II 44 provided with a pre-reflux pump 45; the steam at the top of the pre-distillation column 1 provides heat for the atmospheric column reboiler 27, and further provides energy required for rectification of the atmospheric column 4, the heat-exchanged material enters the extraction tank 40 for extraction, the liquid phase after extraction is refluxed to the pre-distillation column 1 for continuous rectification, and the gas phase is extracted through the vent gas pipeline 43; the above is used for removing impurities and discharging gas, realizing stable operation and high energy consumption control of the process flow; the top of the negative pressure column 2 is connected with a negative pressure column reflux tank 47 through a negative pressure column overhead pipeline 46 provided with a negative pressure column condenser 48, the negative pressure column 3 is connected with the negative pressure column condenser 48 through a negative pressure column overhead pipeline 32, the top of the negative pressure column reflux tank 47 is connected with a negative pressure column vacuum system 49, the negative pressure column vacuum system 49 adopts the existing chemical vacuum system in the prior art, and the present application does not make any improvement on it; the negative pressure column vacuum system 49 maintains a low pressure operating condition, which can ensure that the negative pressure column 2 operates in a vacuum environment, because the negative pressure column reflux tank 47 is in gas communication with the negative pressure column 2, so the negative pressure column reflux tank 47 is also under negative pressure; the bottom of the negative pressure column reflux tank 47 is connected with the middle-upper part of the negative pressure column 2 through a negative pressure column reflux pipeline 50 provided with a negative pressure column reflux pump 51, the bottom of the negative pressure column reflux tank 47 is also connected with the negative pressure column 3 through a negative pressure column-decompression column reflux pipeline 99 provided with a negative pressure column-decompression column reflux pump; the negative pressure column reflux pipeline 50 and the negative pressure column-decompression column reflux pipeline 99 are connected with a negative pressure column refined methanol extraction pipeline 52; as is known, corresponding valves are respectively arranged on the negative pressure column reflux pipeline 50 and the negative pressure column-decompression column reflux pipeline 99, when the negative pressure column 2 works, the reflux is controlled to the negative pressure column 2, and when the negative pressure column 2 does not work, the reflux is controlled to the negative pressure column 3; preferably, the negative pressure column refined methanol extraction pipeline 52 is connected with a product methanol tank 53, and the negative pressure column refined methanol extraction pipeline 52 is provided with a negative pressure column refined methanol cooler 54; when the negative pressure column 2 works, the steam at the top of the negative pressure column 2 enters the negative pressure column reflux tank 47 after being condensed by the negative pressure column condenser 48, the negative pressure column reflux tank 47 is kept in a vacuum state, part of the liquid phase in the negative pressure column reflux tank 47 is extracted as refined methanol, and part of the liquid phase is refluxed to the negative pressure column 2 for continuous rectification, so that the rectification precision is improved; preferably, the extracted refined methanol is cooled by the negative pressure column refined methanol cooler 54 and then stored in the product methanol tank 53.When the cold source of the negative pressure column condenser 48 is insufficient, the negative pressure column 2 does not work, and the gas phase at the top of the vacuum column 3 directly enters the negative pressure column condenser 48, and after being condensed by the negative pressure column condenser 48, enters the negative pressure column reflux tank 47, and the negative pressure column reflux tank 47 is kept in a vacuum state, part of the liquid phase in the negative pressure column reflux tank 47 is taken out as refined methanol, and part of the liquid phase is refluxed to the vacuum column 3 for further rectification.

[0104] The output end of the negative pressure column reboiler 25 is connected with the vacuum column reflux tank 56 through the vacuum column reflux pipeline one 55, the top of the vacuum column reflux tank 56 is connected with the vacuum system 57 of the vacuum column, the vacuum system 57 of the vacuum column maintains a low pressure operation condition, which can ensure that the vacuum column 3 operates in a vacuum environment, because the vacuum column reflux tank 56 is communicated with the vacuum column 3, so the vacuum column reflux tank 56 is also under negative pressure; the bottom of the vacuum column reflux tank 56 is connected with the top of the vacuum column 3 through the vacuum column reflux pipeline two 58, the vacuum column reflux pipeline two 58 is provided with the vacuum column reflux pump 59, and the vacuum column reflux pipeline two 58 is connected with the refined methanol outlet pipeline 60 of the vacuum column; preferably, the refined methanol outlet pipeline 60 of the vacuum column is connected with the product methanol tank 53, and the refined methanol outlet pipeline 60 of the vacuum column is provided with the refined methanol cooler 61 of the vacuum column; the steam at the top of the vacuum column 3 provides heat for the negative pressure column reboiler 25, and further provides energy required for rectification of the negative pressure column 2, and the heat-exchanged material enters the vacuum column reflux tank 56, the vacuum column reflux tank 56 maintains a vacuum state, part of the liquid phase in the vacuum column reflux tank 56 is taken out as refined methanol, and part of the liquid phase is refluxed to the vacuum column 3 for further rectification, so that the precision of rectification is improved; preferably, the refined methanol is stored in the product methanol tank 53 after being cooled by the refined methanol cooler 61 of the vacuum column.

[0105] The output end of the negative pressure column reboiler 25 is connected with the vacuum column reflux tank 56 through the vacuum column reflux pipeline one 55, the top of the vacuum column reflux tank 56 is connected with the vacuum system 57 of the vacuum column, the vacuum system 57 of the vacuum column maintains a low pressure operation condition, which can ensure that the vacuum column 3 operates in a vacuum environment, because the vacuum column reflux tank 56 is communicated with the vacuum column 3, so the vacuum column reflux tank 56 is also under negative pressure; the bottom of the vacuum column reflux tank 56 is connected with the top of the vacuum column 3 through the vacuum column reflux pipeline two 58, the vacuum column reflux pipeline two 58 is provided with the vacuum column reflux pump 59, and the vacuum column reflux pipeline two 58 is connected with the refined methanol outlet pipeline 60 of the vacuum column; preferably, the refined methanol outlet pipeline 60 of the vacuum column is connected with the product methanol tank 53, and the refined methanol outlet pipeline 60 of the vacuum column is provided with the refined methanol cooler 61 of the vacuum column; the steam at the top of the vacuum column 3 provides heat for the negative pressure column reboiler 25, and further provides energy required for rectification of the negative pressure column 2, and the heat-exchanged material enters the vacuum column reflux tank 56, the vacuum column reflux tank 56 maintains a vacuum state, part of the liquid phase in the vacuum column reflux tank 56 is taken out as refined methanol, and part of the liquid phase is refluxed to the vacuum column 3 for further rectification, so that the precision of rectification is improved; preferably, the refined methanol is stored in the product methanol tank 53 after being cooled by the refined methanol cooler 61 of the vacuum column.

[0106] The output end of the pre-column reboiler 24 is connected with a medium-pressure reflux tank 69 through a medium-pressure reflux pipeline I 68, the bottom of the medium-pressure reflux tank 69 is connected with a medium-pressure column 5 through a medium-pressure reflux pipeline II 70, a medium-pressure reflux pump 71 is arranged on the medium-pressure reflux pipeline II 70, and the medium-pressure reflux pipeline II 70 is connected with a medium-pressure column refined methanol extraction pipeline 72; preferably, the medium-pressure column refined methanol extraction pipeline 72 is connected with a product methanol tank 53, and a medium-pressure column refined methanol cooler 73 is arranged on the medium-pressure column refined methanol extraction pipeline 72; the steam at the top of the medium-pressure column 5 provides heat for the pre-column reboiler 24, and further provides energy required for rectification for the pre-rectification column 1; the material after heat exchange enters the medium-pressure reflux tank 69, part of the liquid phase in the medium-pressure reflux tank 69 is extracted as refined methanol, and part of the liquid phase is refluxed to the medium-pressure column 5 to continue rectification, so that the precision of rectification is improved; the extracted refined methanol is stored in the product methanol tank 53 after being cooled by the medium-pressure column refined methanol cooler 73; preferably, the medium-pressure column refined methanol extraction pipeline 72 passes through a medium-pressure column preheater 15 to exchange heat with the feed of the medium-pressure column, and specifically, the medium-pressure column refined methanol extraction pipeline 72 is connected with the input end and the output end of the medium-pressure column preheater 15 respectively.

[0107] The output end of the pre-column reboiler 24 is connected with a medium-pressure reflux tank 69 through a medium-pressure reflux pipeline I 68, the bottom of the medium-pressure reflux tank 69 is connected with a medium-pressure column 5 through a medium-pressure reflux pipeline II 70, a medium-pressure reflux pump 71 is arranged on the medium-pressure reflux pipeline II 70, and the medium-pressure reflux pipeline II 70 is connected with a medium-pressure column refined methanol extraction pipeline 72; preferably, the medium-pressure column refined methanol extraction pipeline 72 is connected with a product methanol tank 53, and a medium-pressure column refined methanol cooler 73 is arranged on the medium-pressure column refined methanol extraction pipeline 72; the steam at the top of the medium-pressure column 5 provides heat for the pre-column reboiler 24, and further provides energy required for rectification for the pre-rectification column 1; the material after heat exchange enters the medium-pressure reflux tank 69, part of the liquid phase in the medium-pressure reflux tank 69 is extracted as refined methanol, and part of the liquid phase is refluxed to the medium-pressure column 5 to continue rectification, so that the precision of rectification is improved; the extracted refined methanol is stored in the product methanol tank 53 after being cooled by the medium-pressure column refined methanol cooler 73; preferably, the medium-pressure column refined methanol extraction pipeline 72 passes through a medium-pressure column preheater 15 to exchange heat with the feed of the medium-pressure column, and specifically, the medium-pressure column refined methanol extraction pipeline 72 is connected with the input end and the output end of the medium-pressure column preheater 15 respectively.

[0108] The output end of the pressurized column reboiler 29 is connected with a high-pressure column backflow tank 81 through a high-pressure column backflow pipeline 1 80, the bottom of the high-pressure column backflow tank 81 is connected with the high-pressure column 7 through a high-pressure column backflow pipeline 2 82, a high-pressure column backflow pump 83 is arranged on the high-pressure column backflow pipeline 2 82, and the high-pressure column backflow pipeline 2 82 is connected with a high-pressure column refined methanol production pipeline 84; preferably, the high-pressure column refined methanol production pipeline 84 is connected with a product methanol tank 53, and a high-pressure column refined methanol cooler 85 is arranged on the high-pressure column refined methanol production pipeline 84; the steam at the top of the high-pressure column 7 provides heat for the pressurized column reboiler 29, and further provides energy required for rectification of the pressurized column 6; the material after heat exchange enters the high-pressure column backflow tank 81, part of the liquid phase in the high-pressure column backflow tank 81 is taken out as refined methanol, and the other part is backflowed to the high-pressure column 7 to continue rectification, so that the precision of rectification is improved; preferably, the refined methanol after cooling by the high-pressure column refined methanol cooler 85 is stored in the product methanol tank 53; more preferably, the high-pressure column refined methanol production pipeline 84 is connected with the input end and the output end of the high-pressure column preheater 1 19, the refined methanol provides heat for the high-pressure column preheater 1 19, and the refined methanol after heat exchange is taken out.

[0109] Embodiment six:

[0110] The embodiment provides a specific application occasion:

[0111] In the embodiment, a specific application is provided, taking the seven-column system of embodiment five and the process of embodiment one as an example, the crude methanol feed quantity is 44000 kg / h, the water content is 6.56%, and the ethanol content is about 600 ppm; by the application, the steam energy consumption of refined methanol is about 0.2492 tons of steam / refined methanol, the methanol purity can reach more than 99.99%, and the ethanol content is less than 100 ppm; the operation parameters of each column are shown in Table 2:

[0112]

[0113] The crude methanol complete cascade multi-effect rectification device provided by the application is sequentially connected with a pre-rectification column 1, a negative-pressure column 2, a reduced-pressure column 3, an atmospheric-pressure column 4, a medium-pressure column 5, a pressurized column 6 and a high-pressure column 7, and the feed is input into the system through a feed pipeline 8. The bottoms of the columns are respectively provided with a pre-column reboiler 24, a negative-pressure column reboiler 25, a reduced-pressure column reboiler 26, an atmospheric-pressure column reboiler 27, a medium-pressure column reboiler 28, a pressurized column reboiler 29 and a high-pressure column reboiler 30;

[0114] Pre-tower kettle pipeline 11, negative pressure tower kettle pipeline 12, vacuum tower kettle pipeline 13, atmospheric tower kettle pipeline 14, medium pressure tower kettle pipeline 16, pressurized tower kettle pipeline 18, pre-tower preheater 1 9, pre-tower preheater 2 10, medium pressure tower preheater 15, pressurized tower preheater 17, high pressure tower preheater 1 9, high pressure tower preheater 2 20, high pressure tower preheater 3 21 are connected, each tower kettle pipeline is connected with the corresponding preheater to form a complete preheating and reboiling circulation loop, and is discharged and intermediate production through waste water pipeline 23 and side production pipeline 22.

[0115] In the heat coupling layout, the overhead gas of pre-distillation tower 1, vacuum tower 3, atmospheric tower 4, medium pressure tower 5, pressurized tower 6 and high pressure tower 7 passes through atmospheric tower reboiler 27, negative pressure tower reboiler 25, vacuum tower reboiler 26, pre-tower reboiler 24, medium pressure tower reboiler 28 and pressurized tower reboiler 29 in turn through pre-tower overhead pipeline 31, vacuum tower overhead pipeline 32, atmospheric tower overhead pipeline 33, medium pressure tower overhead pipeline 34, pressurized tower overhead pipeline 35, high pressure tower overhead pipeline 36, forming a complete cascade multi-effect heat coupling system, high pressure tower reboiler 30 uses medium pressure steam or low pressure steam delivered by steam pipeline 37 to supply heat, and the steam condensate is discharged after heat exchange with high pressure tower preheater 3 21 and pre-tower preheater 2 10 in turn through condensate pipeline 38, improving heat energy utilization efficiency and reducing steam consumption.

[0116] Further, the second reboilers can be additionally provided in the kettle of the pre-fractionating column 1, the negative pressure column 2, the reduced pressure column 3, the normal pressure column 4, and the medium pressure column 5 according to the actual coupling condition and the heat source condition on site, and the external low-temperature waste heat is used for partial heating, so that the steam consumption is further reduced while the product quality is maintained; specifically, when the low-temperature heat source on site is more than 60℃, the second reboiler 100 of the negative pressure column is arranged in the kettle of the negative pressure column 2, and the low-temperature heat source is used for heating the second reboiler 100 of the negative pressure column; the low-temperature heat source includes but is not limited to steam condensate, synthesis gas and other rich low-temperature heat sources; when the low-temperature heat source on site is more than 70℃, the second reboiler 101 of the reduced pressure column and the second reboiler 100 of the negative pressure column are arranged in the kettle of the reduced pressure column 3 and the kettle of the negative pressure column 2 respectively, and the low-temperature heat source is used for heating the second reboiler 101 of the reduced pressure column and the second reboiler 100 of the negative pressure column in sequence; when the low-temperature heat source on site is more than 80℃, the second reboiler 102 of the normal pressure column, the second reboiler 101 of the reduced pressure column and the second reboiler 100 of the negative pressure column are arranged in the kettle of the normal pressure column 4, the kettle of the reduced pressure column 3 and the kettle of the negative pressure column 2 respectively, and the low-temperature heat source is used for heating the second reboiler 102 of the normal pressure column, the second reboiler 101 of the reduced pressure column and the second reboiler 100 of the negative pressure column in sequence; when the low-temperature heat source on site is more than 100℃, the second reboiler 86 of the pre-fractionating column, the second reboiler 102 of the normal pressure column, the second reboiler 101 of the reduced pressure column and the second reboiler 100 of the negative pressure column are arranged in the kettle of the pre-fractionating column 1, the kettle of the normal pressure column 4, the kettle of the reduced pressure column 3 and the kettle of the negative pressure column 2 respectively, and the low-temperature heat source is used for heating the second reboiler 86 of the pre-fractionating column, the second reboiler 102 of the normal pressure column, the second reboiler 101 of the reduced pressure column and the second reboiler 100 of the negative pressure column in sequence; when the low-temperature heat source on site is more than 120℃, the second reboiler 103 of the medium pressure column, the second reboiler 86 of the pre-fractionating column, the second reboiler 102 of the normal pressure column, the second reboiler 101 of the reduced pressure column and the second reboiler 100 of the negative pressure column are arranged in the kettle of the medium pressure column 5, the kettle of the pre-fractionating column 1, the kettle of the normal pressure column 4, the kettle of the reduced pressure column 3 and the kettle of the negative pressure column 2 respectively, and the low-temperature heat source is used for heating the second reboiler 103 of the medium pressure column, the second reboiler 86 of the pre-fractionating column, the second reboiler 102 of the normal pressure column, the second reboiler 101 of the reduced pressure column and the second reboiler 100 of the negative pressure column in sequence.

[0117] In the initial stage, the crude methanol is fed into each column, and the steam pipeline 37 is used to heat the high-pressure column reboiler 30 to gradually establish the temperature gradient of each column, specifically:

[0118] The crude methanol enters a pre-column pre-heater 9 and a pre-column pre-heater 10 for pre-heating, and is pre-heated to about 80°C. The pre-heated crude methanol enters a pre-distillation column 1 for distillation. The pre-distillation column 1 has a top pressure of 170 KPa, a top temperature of 81°C, and a bottom temperature of 83°C. The gas phase taken from the top of the pre-distillation column 1 is used to provide heat for the distillation of a normal-pressure column 4 in a normal-pressure column reboiler 27. After being cooled by a pre-column condenser 41, the gas phase enters an extraction tank 40. The non-condensable gas produced in the extraction tank 40 is discharged. The liquid phase produced after extraction is returned to the pre-distillation column 1.

[0119] The liquid phase taken from the bottom of the pre-distillation column 1 is cooled by heat exchange with the pre-column pre-heater 9, and then enters a negative-pressure column 2. The negative-pressure column 2 has a top pressure of 40 KPa, a top temperature of 43°C, and a bottom temperature of 50°C. The gas phase taken from the top of the negative-pressure column 2 is condensed by a negative-pressure column condenser 48, and then enters a negative-pressure column return tank 47. The liquid phase in the negative-pressure column return tank 47 is divided into two streams. One of the streams is returned to the negative-pressure column 2, and the other stream is taken as refined methanol. The heat required by the negative-pressure column reboiler 25 is provided by the methanol vapor from the top of a vacuum column 3. The vacuum environment of the negative-pressure column 2 is provided by a negative-pressure column vacuum system 49.

[0120] The material taken from the bottom of the negative-pressure column 2 enters the vacuum column 3 for distillation. The vacuum column 3 has a top pressure of 70 KPa, a top temperature of 55°C, and a bottom temperature of 63°C. The gas phase taken from the top of the vacuum column 3 is heated by the negative-pressure column reboiler 25, and then enters a vacuum column return tank 56. The liquid phase in the vacuum column return tank 56 is divided into two streams. One of the streams is returned to the vacuum column 3, and the other stream is taken as refined methanol. The heat required by the vacuum column reboiler 26 is provided by the methanol vapor from the top of the normal-pressure column 4. The vacuum environment of the vacuum column 3 is provided by a vacuum column vacuum system 57.

[0121] The material taken from the bottom of the vacuum column 3 enters the normal-pressure column 4 for distillation. The normal-pressure column 4 has a top pressure of 115 KPa, a top temperature of 68°C, and a bottom temperature of 76°C. The gas phase taken from the top of the normal-pressure column 4 is heated by the vacuum column reboiler 26, and then enters a normal-pressure column return tank 63. The liquid phase in the normal-pressure column return tank 63 is divided into two streams. One of the streams is returned to the normal-pressure column 4, and the other stream is taken as refined methanol. The heat required by the normal-pressure column reboiler 27 is provided by the vapor from the top of the pre-distillation column 1.

[0122] The tower bottom liquid of the atmospheric column 4 is preheated by the medium pressure column preheater 15 and then enters the medium pressure column 5 for further rectification. The medium pressure column 5 has a top pressure of 300 KPa, a top temperature of 95°C and a bottom temperature of 109°C. The gaseous phase taken from the top of the medium pressure column 5 enters the pre-column reboiler 24 to provide the heat required for rectification of the pre-distillation column 1. After heat exchange, the gaseous phase enters the medium pressure column reflux tank 69. The liquid phase in the medium pressure column reflux tank 69 is divided into two streams. One stream is refluxed to the medium pressure column 5, and the other stream is preheated by the medium pressure column preheater 15 and then taken as refined methanol.

[0123] The tower bottom liquid of the medium pressure column 5 is preheated by the pressurized column preheater 17 and then enters the pressurized column 6 for further rectification. The pressurized column 6 has a top pressure of 550 KPa, a top temperature of 115°C and a bottom temperature of 132°C. The gaseous phase taken from the top of the pressurized column 6 enters the medium pressure column reboiler 28 to provide the heat required for rectification of the medium pressure column 5. After heat exchange, the gaseous phase enters the pressurized column reflux tank 75. The liquid phase in the pressurized column reflux tank 75 is divided into two streams. One stream is refluxed to the pressurized column 6, and the other stream is preheated by the pressurized column preheater 17 and then taken as refined methanol.

[0124] The tower bottom liquid of the pressurized column 6 is preheated by the high pressure column preheater one 19, the high pressure column preheater two 20 and the high pressure column preheater three 21 in sequence and then enters the high pressure column 7 for further rectification. The high pressure column 7 has a top pressure of 1050 KPa, a top temperature of 139°C and a bottom temperature of 182°C. The gaseous phase taken from the top of the high pressure column 7 enters the pressurized column reboiler 29 to provide the heat required for rectification of the pressurized column 6. After condensation, the gaseous phase enters the high pressure column reflux tank 81. The liquid phase in the high pressure column reflux tank 81 is divided into two streams. One stream is refluxed to the pressurized column 6, and the other stream is preheated by the high pressure column preheater one 19 and then taken as refined methanol. The side take-off line 22 of the high pressure column 7 takes off fusel alcohol. The tower bottom liquid taken from the bottom of the high pressure column 7 is preheated by the high pressure column preheater two 20 and then taken as waste water. The high pressure column 7 is indirectly heated by the high pressure column reboiler 30 to provide the heat required for rectification of the high pressure column 7. The heat source of the high pressure column reboiler 30 is steam. The steam after heat exchange with the high pressure column preheater three 21 and the pre-column preheater two 10 is taken as steam condensate.

[0125] Further, the wastewater from the high-pressure column 7 is used to heat the high-pressure column preheater 2 0, and the heat is reused; the material from the pre-distillation column 1 is used to heat the pre-column preheater 9, and the heat is reused; after the steam provides heat for the high-pressure column reboiler 30, the steam continues to provide heat for the high-pressure column preheater 3 21 and the pre-column preheater 2 10, and the heat is reused; the refined methanol from the high-pressure column 7 is used to heat the high-pressure column preheater 1 19, and the heat is reused; the refined methanol from the pressurizing column 6 is used to heat the pressurizing column preheater 17, and the heat is reused; the refined methanol from the medium-pressure column 5 is used to heat the medium-pressure column preheater 16, and the heat is reused; the reuse of the above heat further reduces the additional energy consumption.

[0126] Example Seven:

[0127] In another specific example, the distillation device of Example Five and the process of Example One are taken as examples:

[0128] In this example, the operating pressures of the pre-distillation column 1, the negative-pressure column 2, the reduced-pressure column 3, the normal-pressure column 4, the medium-pressure column 5, the pressurizing column 6, and the high-pressure column 7 are 0.25 MPa, 25 kPa, 55 kPa, 0.10 MPa, 0.30 MPa, 0.55 MPa, and 1.20 MPa, respectively. Crude methanol with a water content of 12.0% is subjected to distillation according to the present application. After 24 hours of equilibrium, the mass fraction of refined methanol in the product methanol tank 53 is ≥99.99%, and the flow rate of fusel alcohol collected by the side collecting pipeline 22 is 0.35 t·h -1 . The wastewater from the high-pressure column 7 is discharged through the wastewater pipeline 23, and the methanol content in the wastewater is ≤150 mg·L -1 .

[0129] Example Eight:

[0130] In another specific example, the distillation device of Example Five and the process of Example One are taken as examples:

[0131] In this example, the operating pressures of the pre-distillation column 1, the negative-pressure column 2, the reduced-pressure column 3, the normal-pressure column 4, the medium-pressure column 5, the pressurizing column 6, and the high-pressure column 7 are 0.25 MPa, 30 kPa, 65 kPa, 0.10 MPa, 0.30 MPa, 0.55 MPa, and 1.20 MPa, respectively. Crude methanol with a water content of 15.0% (80 t·h -1 ) is subjected to distillation according to the present application. After continuous operation, the mass fraction of refined methanol is ≥99.95%, and the flow rate of fusel alcohol collected by the side collecting pipeline 22 is increased to 0.42 t·h -1 . The steam consumption is 0.21 t of steam (t of methanol) -1 .

[0132] Example Nine:

[0133] Another specific embodiment is described below with reference to the rectification device of Example Five and the process of Example One.

[0134] A parallel aldehyde extraction branch is added at the top of the atmospheric column 4, and a gas phase water washing column is connected in parallel with the atmospheric column reflux tank 63. The remaining equipment is the same as in Example Five. The raw material is crude methanol (60 t.h -1 ) containing 1.5% aldehyde impurities. At the top of the atmospheric column 4, 90% of the gas phase is still supplied to the vacuum column reboiler 26 through the atmospheric column overhead line 33, and 10% of the gas phase is supplied to the gas phase water washing column and then refluxed to the atmospheric column reflux tank 63.

[0135] Operation results: aldehyde content ≤4 mg·kg -1 , refined methanol yield 97.2%, steam consumption 0.245 t steam (t methanol) -1 .

[0136] Example Ten

[0137] On the basis of Example One and Example Five, the gas phase at the top of the high-pressure column 7 is sent to a mechanical steam re-compressor unit (compression ratio 1.35) to increase the temperature, and then exchanges heat with the pressurized column reboiler 29, replacing the direct exchange of heat between the gas phase at the top of the high-pressure column 7 and the pressurized column reboiler 29 through the overhead line 36. The high-pressure column reboiler 30 is supplemented with 0.25 MPa g low-pressure steam.

[0138] After balanced operation, the net steam consumption is reduced to 0.155 t (t methanol) -1 , and the total energy consumption cost is reduced by 14.6%.

[0139] Example Eleven

[0140] On the basis of Example One and Example Five, the packing of the medium-pressure column 5 and the pressurized column 6 is replaced with stainless steel float valve trays, and the medium-pressure column reflux pump 71 and the pressurized column reflux pump 77 maintain the original flow rate, with only a slight adjustment of the reflux ratio (adjusted by the automatic control system). The other pipelines and thermal couplings remain unchanged.

[0141] The theoretical plate number of the medium-pressure column 5 and the pressurized column 6 is reduced by 18.5% respectively, and the system pressure drop is reduced by 8.4 kPa. The refined methanol purity is above 99.97%, and the steam consumption is 0.232 t steam (t methanol) -1 .

[0142] Example Twelve

[0143] In the embodiment one, the embodiment five, the distributed control system is configured in each of the top of the pre-fractionation column 1, the negative pressure column 2, the vacuum column 3, the atmospheric column 4, the medium pressure column 5, the pressurized column 6 and the high pressure column 7, the methanol volume fraction is fed back to the control valve by the online chromatograph, the frequency of the pre-reflux pump 45, the negative pressure reflux pump 51, the vacuum reflux pump 59, the atmospheric reflux pump 65, the medium pressure reflux pump 71, the pressurized reflux pump 77 and the high pressure reflux pump 83 is automatically adjusted, the high pressure column reboiler 30 steam valve is closed loop with the top pressure of the high pressure column 7, and the sampling cycle is 5s.

[0144] The continuous 72h operation, the purity of the refined methanol is ±0.02%, the yield of the side sampling pipeline 22 is increased by 12%.

[0145] In summary, in the application, the methanol steam at the top of the high pressure column is heated to realize heat coupling of the pressurized column bottom; the methanol steam at the top of the pressurized column is heated to realize heat coupling of the medium pressure column bottom; the methanol steam at the top of the medium pressure column is heated to realize heat coupling of the pre-fractionation column bottom; the steam at the top of the pre-column is heated to realize heat coupling of the atmospheric column bottom; the methanol steam at the top of the atmospheric column is heated to realize heat coupling of the vacuum column bottom; the methanol steam at the top of the vacuum column is heated to realize heat coupling of the negative pressure column bottom; the application realizes seven-effect utilization of steam, and the energy-saving effect is remarkable; compared with the traditional methanol process, the steam consumption can be reduced to 0.20-0.30t steam / t refined alcohol; compared with the traditional two-tower heat coupling process, more than 70% of energy can be saved, the operation cost of the enterprise is greatly reduced, the carbon emission is significantly reduced, and the competitiveness of the enterprise is improved; further, the vacuum column top steam can be switched to be connected with the negative pressure column top condenser, the negative pressure column is cut off under the condition of insufficient cold source, six-tower operation is carried out; under the condition of sufficient cold source, a vacuum tower can be arranged before the pre-fractionation column and the negative pressure column, the vacuum tower reboiler is heated by the negative pressure column top steam, and eight-tower series operation is realized.

[0146] The application can realize overall optimization of performance of the system by increasing the number of towers and enhancing the coupling effect between the towers, especially further reducing energy consumption and the parallel operation process parameter controllability problem; the coupling effect between the towers of the application mainly has the following advantages: (1) more energy-saving: the heat transfer temperature difference is reduced, the thermodynamic reversibility of the system is increased, and the heat consumption is reduced; (2) more stable: through gradient temperature difference control, multiple tower products, mutual balance of indexes, avoiding the influence of single link fluctuation on the whole system, ensuring that the system stability is stronger; (3) more flexible: the application distributes the load to multiple towers to adapt and bear respectively, adjusts the preheating mode and increases the second reboiler to increase the system operation flexibility, so that the system operation flexibility is increased and the capacity elasticity is improved.

[0147] The devices and connection relationships not specifically described above all belong to the prior art, and the application will not be specifically described here.

[0148] The preferred mode of the present application is described in detail above with reference to the accompanying drawings, but the present application is not limited to the specific details of the above-described embodiments. Various simple modifications can be made to the technical solutions of the present application within the scope of the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0149] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations of the present application are not described again.

[0150] In addition, various different embodiments of the present application can also be combined in any appropriate manner, as long as they do not deviate from the idea of the present application, and the application should also be considered as disclosed content of the present application.

Claims

1. A complete cascade multi-effect distillation process for crude methanol, characterized in that: The method comprises a pre-distillation tower (1), a negative pressure tower (2), a vacuum tower (3), an atmospheric pressure tower (4), a medium pressure tower (5), a pressure tower (6), and a high pressure tower (7) which are connected in sequence, wherein the pressure of the negative pressure tower (2), the vacuum tower (3), the atmospheric pressure tower (4), the medium pressure tower (5), the pressure tower (6), and the high pressure tower (7) increases step by step; The crude methanol enters the pre-distillation tower (1) for distillation. The gas phase extracted from the top of the pre-distillation tower (1) goes to the atmospheric tower reboiler (27) to provide the heat required for distillation for the atmospheric tower (4). The liquid phase extracted from the bottom of the pre-distillation tower (1) enters the negative pressure tower (2) or the vacuum tower (3). When the liquid phase extracted from the bottom of the pre-distillation tower (1) enters the negative pressure tower (2), the gas phase extracted from the top of the negative pressure tower (2) is condensed by the negative pressure tower condenser (48) and enters the negative pressure tower reflux tank (47). The liquid phase in the negative pressure tower reflux tank (47) is divided into two streams, one of which is refluxed to the negative pressure tower (2) and the other is extracted as refined methanol. The vacuum environment of the negative pressure tower (2) is provided by the negative pressure tower vacuum system (49); the material in the bottom of the negative pressure tower (2) enters the vacuum tower (3) and enters the vacuum tower The gas phase extracted from the top of the vacuum tower (3) is sent to the negative pressure tower reboiler (25) to provide the heat required for distillation for the negative pressure tower (2). The gas phase extracted from the top of the vacuum tower (3) is heat-exchanged with the negative pressure tower reboiler (25) and then enters the vacuum tower reflux tank (56). The liquid phase of the vacuum tower reflux tank (56) is divided into two streams, one of which is refluxed to the vacuum tower (3) and the other is extracted as refined methanol. The vacuum environment of the vacuum tower (3) is provided by the vacuum tower vacuum system (57); When the liquid phase extracted from the bottom of the pre-distillation tower (1) enters the vacuum tower (3), the gas phase extracted from the top of the vacuum tower (3) goes to the negative pressure tower condenser (48), is condensed in the negative pressure tower condenser (48), and then enters the negative pressure tower reflux tank (47). The liquid phase in the negative pressure tower reflux tank (47) is divided into two streams, one of which is refluxed to the vacuum tower (3), and the other is extracted as refined methanol; The materials in the bottom of the vacuum tower (3) enter the atmospheric tower (4) for rectification, and the gas phase extracted from the top of the atmospheric tower (4) goes to the vacuum tower reboiler (26) to provide the heat required for rectification for the vacuum tower (3); the gas phase extracted from the top of the atmospheric tower (4) exchanges heat with the vacuum tower reboiler (26) and then enters the atmospheric tower reflux tank (63), and the liquid phase in the atmospheric tower reflux tank (63) is divided into two streams, one of which is refluxed to the atmospheric tower (4), and the other is extracted as refined methanol; The bottom liquid of the atmospheric tower (4) enters the medium-pressure tower (5) for further distillation. The gas phase extracted from the top of the medium-pressure tower (5) goes to the pre-tower reboiler (24) to provide the heat required for distillation for the pre-distillation tower (1). The gas phase extracted from the top of the medium-pressure tower (5) enters the medium-pressure tower reflux tank (69) after heat exchange in the pre-tower reboiler (24). The liquid phase in the medium-pressure tower reflux tank (69) is divided into two streams, one of which is refluxed to the medium-pressure tower (5) and the other is extracted as refined methanol. The bottom liquid of the medium-pressure tower (5) enters the pressure tower (6) for further distillation, and the gas phase extracted from the top of the pressure tower (6) goes to the medium-pressure tower reboiler (28) to provide the heat required for distillation for the medium-pressure tower (5); the gas phase extracted from the top of the pressure tower (6) exchanges heat with the medium-pressure tower reboiler (28) and then enters the pressure tower reflux tank (75), and the liquid phase in the pressure tower reflux tank (75) is divided into two streams, one of which is refluxed to the pressure tower (6) and the other is extracted as refined methanol; The bottom of the pressure tower (6) enters the high-pressure tower (7) to continue distillation, and the gas phase at the top of the high-pressure tower (7) goes to the pressure tower reboiler (29) to provide the heat required for distillation for the pressure tower (6); the gas phase at the top of the high-pressure tower (7) goes to the pressure tower reboiler (29) for heat exchange and then enters the high-pressure tower reflux tank (81), and the liquid phase in the high-pressure tower reflux tank (81) is divided into two streams, one of which is refluxed to the pressure tower (6) and the other is produced as refined methanol; the side production line (22) of the high-pressure tower (7) produces fusel alcohol, and the bottom of the high-pressure tower (7) produces waste water; the high-pressure tower (7) provides the heat required for distillation of the high-pressure tower (7) in the form of indirect heating through the high-pressure tower reboiler (30), and the heat source of the high-pressure tower reboiler (30) is steam.

2. A complete cascade multi-effect distillation process for crude methanol according to claim 1, characterized in that: When the low-temperature heat source at the distillation site exceeds 60°C, a second reboiler (100) of the negative pressure tower is provided in the tower kettle of the negative pressure tower (2), and the low-temperature heat source is used to supply heat to the second reboiler (100) of the negative pressure tower; when the low-temperature heat source at the distillation site exceeds 70°C, a second reboiler (101) of the negative pressure tower and a second reboiler (100) of the negative pressure tower are provided in the tower kettle of the vacuum tower (3) and the tower kettle of the negative pressure tower (2), respectively, and the low-temperature heat source sequentially supplies heat to the second reboiler (101) of the vacuum tower and the second reboiler (100) of the negative pressure tower; the low-temperature heat source at the distillation site is used to supply heat to the second reboiler (101) of the vacuum tower and the second reboiler (100) of the negative pressure tower; When the heat source exceeds 80°C, the tower kettle of the atmospheric tower (4), the tower kettle of the vacuum tower (3), and the tower kettle of the negative pressure tower (2) are respectively provided with the atmospheric tower second reboiler (102), the vacuum tower second reboiler (101), and the negative pressure tower second reboiler (100), and the low-temperature heat source is sequentially provided by the atmospheric tower second reboiler (102), the vacuum tower second reboiler (101), and the negative pressure tower second reboiler (100); when the low-temperature heat source at the distillation site exceeds 100°C, the tower kettle of the pre-distillation tower (1), the tower kettle of the atmospheric tower (4), the vacuum tower second reboiler (101), and the negative pressure tower second reboiler (100) are provided with the low-temperature heat source. The tower kettle of the tower (3) and the tower kettle of the negative pressure tower (2) are respectively provided with a pre-tower second reboiler (86), a normal pressure tower second reboiler (102), a vacuum tower second reboiler (101), and a negative pressure tower second reboiler (100); the low-temperature heat sources are the pre-tower second reboiler (86), the normal pressure tower second reboiler (102), the vacuum tower second reboiler (101), and the negative pressure tower second reboiler (100) in sequence; when the low-temperature heat source at the distillation site exceeds 120°C, the tower kettle of the medium pressure tower (5), the tower kettle of the pre-distillation tower (1), The tower kettle of the atmospheric tower (4), the tower kettle of the vacuum tower (3), and the tower kettle of the negative pressure tower (2) are respectively provided with a second reboiler of the medium pressure tower (103), a second reboiler of the pre-tower (86), a second reboiler of the atmospheric tower (102), a second reboiler of the vacuum tower (101), and a second reboiler of the negative pressure tower (100); and the low-temperature heat sources are the second reboiler of the medium pressure tower (103), the second reboiler of the pre-tower (86), the second reboiler of the atmospheric tower (102), the second reboiler of the vacuum tower (101), and the second reboiler of the negative pressure tower (86) in sequence.

3. The complete cascade multi-effect distillation process for crude methanol according to claim 1, characterized in that: The logarithmic average temperature difference between the top temperature of the pre-distillation tower (1) and the bottom temperature of the atmospheric pressure tower (4) is 5–12 K, the logarithmic average temperature difference between the top temperature of the vacuum tower (3) and the bottom temperature of the negative pressure tower (2) is 5–12 K, the logarithmic average temperature difference between the top temperature of the atmospheric pressure tower (4) and the bottom temperature of the vacuum tower (3) is 5–12 K, the logarithmic average temperature difference between the top temperature of the medium-pressure tower (5) and the bottom temperature of the pre-distillation tower (1) is 5–12 K, the logarithmic average temperature difference between the top temperature of the pressure tower (6) and the bottom temperature of the medium-pressure tower (5) is 5–12 K, and the logarithmic average temperature difference between the top temperature of the high-pressure tower (7) and the bottom temperature of the pressure tower (6) is 5–12 K.

4. A complete cascade multi-effect distillation process for crude methanol according to claim 1, characterized in that: A vacuum tower is arranged between the pre-distillation tower and the negative pressure tower. A vacuum tower reboiler is arranged at the lower part of the vacuum tower. The steam from the top of the negative pressure tower provides heat for the vacuum tower reboiler.

5. The complete cascade multi-effect distillation process for crude methanol according to claim 1, characterized in that: The bottom liquid of the medium-pressure tower (5) is preheated by the pressure tower preheater (17) and then enters the pressure tower (6) for further distillation; a liquid phase in the pressure tower reflux tank (75) exchanges heat with the pressure tower preheater (17) and is extracted as refined methanol.

6. The complete cascade multi-effect distillation process for crude methanol according to claim 1, characterized in that: The bottom liquid of the pressure tower (6) is heated in sequence by the high-pressure tower preheater 1 (19), the high-pressure tower preheater 2 (20), and the high-pressure tower preheater 3 (21) and then enters the high-pressure tower (7) for further distillation; a liquid phase in the high-pressure tower reflux tank (81) is heat-exchanged with the high-pressure tower preheater 1 (19) and then withdrawn as refined methanol; the waste water withdrawn from the bottom of the high-pressure tower (7) is first heat-exchanged with the high-pressure tower preheater 2 (20) and then withdrawn; the steam after supplying heat to the high-pressure tower reboiler (30) is heat-exchanged with the high-pressure tower preheater 3 (21) and the preheater 2 (10) and then withdrawn as steam condensate.

7. A complete cascade multi-effect distillation device for crude methanol, characterized in that: The invention comprises a pre-rectification tower (1), a negative pressure tower (2), a vacuum tower (3), an atmospheric pressure tower (4), a medium pressure tower (5), a pressure tower (6), and a high pressure tower (7) connected in sequence, wherein the tower kettles of the pre-rectification tower (1), the negative pressure tower (2), the vacuum tower (3), the atmospheric pressure tower (4), the medium pressure tower (5), the pressure tower (6), and the high pressure tower (7) are respectively connected to a pre-tower reboiler (24), a negative pressure tower reboiler (25), a vacuum tower reboiler (26), an atmospheric pressure tower reboiler (27), a medium pressure tower reboiler (28), a pressure tower reboiler (29), and a high pressure tower reboiler (30), wherein the heat source of the high pressure tower reboiler (30) is steam; The top of the distillation tower (1) is connected to the atmospheric pressure tower reboiler (27) via a pre-tower top pipeline (31), the top of the vacuum tower (3) is connected to the negative pressure tower reboiler (25) via a vacuum tower top pipeline (32), the top of the atmospheric pressure tower (4) is connected to the vacuum tower reboiler (26) via a atmospheric pressure tower top pipeline (33), the top of the medium-pressure tower (5) is connected to the pre-tower reboiler (24) via a medium-pressure tower top pipeline (34), the top of the pressure tower (6) is connected to the medium-pressure tower reboiler (28) via a pressure tower top pipeline (35), and the top of the high-pressure tower (7) is connected to the pressure tower reboiler (29) via a high-pressure tower top pipeline (36).

8. A crude methanol complete cascade multi-effect distillation device according to claim 7, characterized in that: The top of the negative pressure tower (2) is connected to the negative pressure tower reflux tank (47) through a negative pressure tower top pipeline (46), and a negative pressure tower condenser (48) is provided on the negative pressure tower top pipeline (46). The vacuum tower (3) is connected to the negative pressure tower condenser (48) through a vacuum tower top pipeline (32). The top of the negative pressure tower reflux tank (47) is connected to a negative pressure tower vacuum system (49). The bottom of the negative pressure tower reflux tank (47) is connected to the middle and upper part of the negative pressure tower (2) through a negative pressure tower reflux pipeline (50). The bottom of the negative pressure tower reflux tank (47) is also connected to the middle and upper part of the vacuum tower (3) through a negative pressure tower-vacuum tower reflux pipeline (99). The negative pressure tower reflux pipeline (50) and the negative pressure tower-vacuum tower reflux pipeline (99) are connected to a negative pressure tower refined methanol extraction pipeline (52).

9. The crude methanol complete cascade multi-effect distillation device according to claim 7, characterized in that: A vacuum tower (87) is provided between the pre-distillation tower (1) and the negative pressure tower (2); the bottom of the vacuum tower (87) is connected to a vacuum tower reboiler (89); and the top of the negative pressure tower (2) is connected to the vacuum tower reboiler (89) via a negative pressure tower top pipeline (46).

10. A crude methanol complete cascade multi-effect distillation device according to claim 9, characterized in that: The tower kettle of the pre-distillation tower (1) is connected to the vacuum tower (87) through the pre-tower tower kettle pipeline (11), the tower kettle of the vacuum tower (87) is connected to the negative pressure tower (2) through the vacuum tower tower kettle pipeline (88), the top of the negative pressure tower (2) is connected to the input end of the vacuum tower reboiler (89) through the negative pressure tower top pipeline (46), the output end of the vacuum tower reboiler (89) is connected to the negative pressure tower reflux tank (47), the top of the negative pressure tower reflux tank (47) is connected to the negative pressure tower vacuum system (49), the bottom of the negative pressure tower reflux tank (47) is connected to the middle and upper part of the negative pressure tower (2) through the negative pressure tower reflux pipeline (50), the negative pressure tower reflux pump (51) is provided on the negative pressure tower reflux pipeline (50), and the negative pressure tower reflux pipeline (50) is connected to the negative pressure tower refined methanol extraction pipeline (52).

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