Low-pressure cross-flow triple-effect dividing-wall tower distillation process and apparatus for crude methanol refining

Abstract

The present invention provides a low-pressure cross-flow triple-effect bulkhead tower distillation process and device for refining crude methanol. The process comprises an atmospheric pressure bulkhead tower, a vacuum tower, and a pressurized tower. The atmospheric pressure bulkhead tower has a top pressure of 130-150 kPa(A) and a top temperature of 70-80°C. The kettle temperature of the atmospheric pressure bulkhead tower is 7-8°C higher than the tower top temperature. The inlet of the pressurized tower is connected to the kettle outlet of the vacuum tower, and 0.6 MPa live steam is used as a heat source. The top pressure of the pressurized tower is 320-340 kPa(A), the top temperature is 96-100°C, and the kettle temperature is 136-140°C. The top pressure of the vacuum tower is 50-60 kPa(A), the top temperature is 48-52°C, and the temperature difference between the top and kettle of the vacuum tower is 7-8°C. The atmospheric pressure tower reboiler, the vacuum tower top reflux, and the second vacuum tower reboiler all partially extract refined methanol. In order to meet the requirements of triple-effect distillation under the premise of using low-pressure steam, realize efficient triple-effect distillation of crude methanol in actual projects and save energy.

Description

Technical Field

[0001] The present invention relates to the technical field of crude methanol refining in coal chemical industry or biomass green methanol process, and specifically to a low-pressure cross-flow three-effect dividing wall tower distillation process and device for crude methanol refining. The process uses low-pressure steam as a heat source and is combined with a dividing wall tower and a cross-flow multiple effect to be used for crude methanol refining. Background Art

[0002] Methanol is a basic chemical raw material with a wide range of applications. Currently, the main sources of methanol are coal-based methanol and biomass methanol (green methanol). In line with the national strategic development needs for energy conservation and consumption reduction, multi-effect distillation and bulkhead thermal coupling are currently recognized as effective energy-saving methods that can be used in methanol refining processes. For example:

[0003] CN 116947605 A discloses a five-tower four-effect crude methanol refining process and apparatus, which adopts a five-tower three-effect separation technology and can be mainly divided into a pre-tower, a pressure reducing tower, a pressure tower, a normal pressure tower and a recovery tower according to the material flow. The operating pressure of the pressure tower is 0.63 MPa (A); the heat source steam pressure of the pressure tower is 1.0 MPa.

[0004] CN 113527058 A discloses a multi-effect methanol distillation method using a side-stream and bulkhead pre-distillation tower with a heat sink. Example 3 employs an atmospheric pressure tower, a medium-pressure tower, and a high-pressure tower. The distillation process sequentially passes through the pre-distillation tower, an atmospheric pressure tower (combined into a bulkhead tower), a medium-pressure tower, and a high-pressure tower. The high-pressure tower has a top pressure of 700 kPa (A), and the steam pressure in the pressurized tower is conservatively greater than 1.0 MPa.

[0005] CN 113289363 A discloses a crude methanol refining and purification system, which adopts a four-tower triple-effect separation process. According to the flow of materials, the system comprises a pre-tower, a medium-pressure tower, a low-pressure tower, and a normal-pressure tower. The top pressure of the medium-pressure tower is 1.1-1.4 MPa, and steam of 1.1-1.3 MPaG needs to be provided to the medium-pressure tower.

[0006] CN 109646980 A discloses an energy-saving device and method for a fusel oil-free final-effect bulkhead tower coupled with a methanol multi-effect distillation. The device utilizes an externally mounted bulkhead tower, consisting of a main tower and an externally suspended auxiliary tower. The device sequence is a lightness removal tower, a high-pressure tower, a medium-pressure tower, and an externally mounted bulkhead tower. Although 600 kPa steam is used for heating, the vapor phase temperature at the top of the medium-pressure tower in the embodiment is 104°C. Considering the effects of the medium-pressure tower pressure drop and increased water content in the bottom of the tower, the bottom temperature of the medium-pressure tower is at least 4°C higher than the top temperature, i.e., the bottom temperature is at least 108°C. The vapor phase temperature at the top of the high-pressure tower is 111.8°C. Even without considering the effects of heat dissipation, the heat transfer temperature difference in the medium-pressure tower reboiler is only 111.8-108 = 3.8°C. Such a small temperature difference, in actual engineering, could result in the heat transfer area of ​​the medium-pressure tower reboiler expanding several times, or even rendering it impossible to operate.

[0007] As can be seen from the above, for the general three-effect methanol refining process, there are certain requirements for the pressure and temperature of the heating steam (heat source). Generally, only when the system increases the steam pressure by more than 1.0MPa can the smooth progress of the three-effect distillation process be guaranteed.

[0008] However, some coal chemical companies have a large surplus of low-pressure steam (0.6MPa), which makes it difficult to meet the design requirements of the triple-effect distillation process at this pressure. Therefore, under low-pressure steam conditions, existing processes generally use single-effect or double-effect evaporation, which consumes a lot of energy.

[0009] Therefore, it is very important to develop and propose a crude methanol three-effect distillation process with low-pressure steam that is suitable for actual engineering operations for energy conservation and emission reduction in most existing enterprises. Summary of the Invention

[0010] The purpose of the present invention is to provide a low-pressure cross-flow three-effect dividing wall tower distillation process and device for crude methanol refining, so as to meet the requirements of three-effect distillation under the premise of using low-pressure steam, realize efficient three-effect distillation of crude methanol in actual engineering, and save energy consumption.

[0011] To achieve the purpose of the present invention, the technical solution provided by the present invention is:

[0012] In a first aspect, the present invention provides a low-pressure cross-flow triple-effect bulkhead tower distillation process for crude methanol refining, the process comprising an atmospheric pressure bulkhead tower 1, a vacuum tower 2, and a pressurized tower 3, the vacuum tower kettle being equipped with a first vacuum tower reboiler and a second vacuum tower reboiler, and the atmospheric pressure bulkhead tower kettle being equipped with an atmospheric pressure tower reboiler;

[0013] The crude methanol is first preheated in the exhaust steam primary cooler 4 at the top of the vacuum tower 2, and then enters the raw material preheater 5 for secondary preheating. After preheating, the crude methanol temperature rises to 70-80°C. It then enters the atmospheric pressure bulkhead tower from the material inlet. The top gas phase on this side enters the reboiler of the first vacuum tower to provide heat and be condensed. The uncondensed light phase gas enters the light hydrocarbon condenser 9 for further condensation, and the tail gas enters the spray absorption tower 10. The condensate from the spray absorption tower 10 is fully refluxed into the atmospheric pressure bulkhead tower on the corresponding side. The top pressure of this side is 130-150KPa(A) and the top temperature is 70-80°C.

[0014] The top pressure of the other side of the atmospheric bulkhead tower is 130-150 kPa (A), and the top gas temperature is 70-80 ° C. The top gas on this side enters the reboiler 8 of the second vacuum tower, and part of the condensed condensate is refluxed into the atmospheric bulkhead tower as the reflux liquid on this side; the bottom temperature of the atmospheric bulkhead tower 1 is 7-8 ° C higher than the top temperature;

[0015] The inlet of the pressure tower is connected to the outlet of the vacuum tower kettle, and 0.6MPa raw steam is used as the heat source; the light phase outlet at the top of the tower is connected to the steam inlet of the atmospheric tower reboiler, which serves as the heat source of the atmospheric tower reboiler. Part of the condensate in the atmospheric tower reboiler flows back to the atmospheric tower, and the rest flows out to the outside as the refined methanol product;

[0016] The outlet of the pressurized tower is pure water, which is discharged after heat recovery, and fusel alcohol is discharged from the side line; the top pressure of the pressurized tower is 320-340KPa (A), the top temperature is 96-100℃, and the bottom temperature is 136-140℃;

[0017] The pressure at the top of the vacuum tower is 50-60 kPa (A), the temperature at the top is 48-52 ° C, and the temperature difference between the top and bottom of the vacuum tower is 7-8 ° C;

[0018] The atmospheric tower reboiler, the vacuum tower top reflux, and the second vacuum tower reboiler all partially produce refined methanol.

[0019] Furthermore, the purity of methanol in the refined methanol is not less than 99.98 wt %.

[0020] Furthermore, the steam temperature of the raw steam is 155-165°C.

[0021] Furthermore, the crude methanol content is 80-93 wt%.

[0022] In a second aspect, the present invention provides a low-pressure cross-flow triple-effect dividing wall tower distillation device for crude methanol refining, the device comprising an atmospheric pressure dividing wall tower 1, a vacuum tower 2 and a pressure tower 3;

[0023] The atmospheric pressure dividing wall tower is composed of a pre-tower and an atmospheric pressure tower. The upper parts of the pre-tower and the atmospheric pressure tower are separated by a partition. The pre-tower and the atmospheric pressure tower are respectively provided with independent gas phase outlets. The lower parts of the two towers share a space and a reboiler.

[0024] The raw material inlet of the pre-tower of the atmospheric pressure dividing wall tower is connected to the upstream crude methanol;

[0025] The top gas phase outlet of the pre-tower is connected to the first vacuum tower reboiler 7, and the first vacuum tower reboiler 7 is respectively connected to the light hydrocarbon condenser 9, the tower kettle of the vacuum tower, and the raw steam condensate preheater 12; the outlet of the light hydrocarbon condenser 9 is connected to the bottom inlet of the spray absorption tower, and the bottom outlet of the spray absorption tower is connected to the top reflux port of the pre-tower; light hydrocarbons are produced at the top of the spray absorption tower, and desalted water enters from the top of the spray absorption tower;

[0026] The top gas phase of the atmospheric tower of the atmospheric bulkhead tower is connected to the second vacuum tower reboiler 8, which is installed in the vacuum tower kettle. Part of the condensate from the second vacuum tower reboiler flows back into the atmospheric tower, and part of it flows out to the outside as a refined methanol product;

[0027] The liquid phase outlet of the tower bottom of the atmospheric pressure dividing wall tower is connected to the material inlet of the vacuum tower 2; the heat source of the atmospheric pressure tower reboiler 6 of the atmospheric pressure dividing wall tower is provided by the top gas phase of the pressure tower;

[0028] The top of the vacuum tower is connected to an exhaust steam primary cooler and a vacuum tower condenser;

[0029] The outlet of the raw steam condensate preheater 12 is connected to the material inlet of the pressurized tower, and the steam inlet of the raw steam condensate preheater 12 is connected to the 0.6 MPa industrial steam supply pipeline through the pressurized tower reboiler;

[0030] The tower kettle of the pressure tower is equipped with a pressure tower reboiler, the top reflux port of the pressure tower is connected to the condensate outlet of the atmospheric tower reboiler, and the top gas phase outlet of the pressure tower is connected to the inlet of the atmospheric tower reboiler; the outlet of the pressure tower reboiler is also connected to the raw material preheater 5;

[0031] The upstream crude methanol is connected to the raw material inlet of the pre-tower after passing through the exhaust steam primary cooler and the raw material preheater, and the waste water is produced in the raw material preheater;

[0032] The atmospheric tower reboiler and the vacuum tower top reflux both produce refined methanol.

[0033] Preferably, the atmospheric pressure dividing wall tower and the pressure tower use full countercurrent TST trays.

[0034] Preferably, the vacuum tower is a packed tower, and the reboiler of the first vacuum tower is a falling film reboiler.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The process of the present invention can achieve efficient triple-effect distillation of crude methanol in actual engineering under the conditions of raw steam pressure of 0.6 MPa (160°C) and cooling water of room temperature water at 25°C (the temperature of the top of the negative pressure tower is 50°C).

[0037] 2. The atmospheric pressure section of the process of the present invention adopts a bulkhead tower structure with a baffle provided inside the bulkhead tower. The pre-tower and atmospheric pressure tower both reflux independently and share a reboiler. Through thermal coupling, this is more conducive to energy saving and heat load matching of the entire system. The process material flow adopts a cross-flow design of atmospheric pressure-reduced pressure-pressurized pressure. The temperature difference between the top and bottom of the three effects can be reduced to about 7°C, 8°C, and 40°C, respectively (i.e., the temperature difference between the top and bottom of the atmospheric pressure bulkhead tower is about 7°C, and the temperature difference between the top and bottom of the vacuum tower is about 8°C. The temperature differences of the two towers are almost the same. The temperature difference between the top and bottom of the pressure tower is about 40°C, which enables refined methanol to be produced from the top of the final pressure tower). The total temperature difference used for heat transfer can reach 58°C, and the average heat transfer temperature difference of each effect is 17-18°C, which can significantly reduce the equipment cost investment of the reboiler of each effect.

[0038] 3. The vacuum tower adopts double reboilers, which can better match the pre-tower and pressure tower of the adjacent tower to ensure the stable operation of the adjacent tower.

[0039] 4. The pressure at the top of the pressure tower in the process of the present invention is 320-340 kPa (A), which is much lower than the pressure of 600 kPa (A) in other processes. This not only makes the operation safer and the operating cost lower, but also reduces the investment in the pressure tower equipment.

[0040] 5. In the methanol refining process of the present invention, the steam consumption per ton of refined methanol can be reduced to less than 0.6 tons, and the purity of the methanol product can exceed 99.98%, thereby obtaining refined methanol. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The present invention is a schematic flow diagram of a low-pressure cross-flow triple-effect dividing wall tower distillation process for crude methanol refining.

[0042] Among them, 1 atmospheric pressure dividing wall tower, 2 vacuum tower, 3 pressurized tower, 4 exhaust steam primary cooler, 5 raw material preheater, 6 atmospheric pressure tower reboiler, 7 first vacuum tower reboiler, 8 second vacuum tower reboiler, 9 light hydrocarbon condenser, 10 spray absorption tower, 11 vacuum tower condenser, 12 live steam condensate preheater, 13 pressurized tower reboiler. DETAILED DESCRIPTION

[0043] The present invention is further explained below with reference to the embodiments and drawings, but they are not intended to limit the scope of protection of the present application.

[0044] The present invention provides a low-pressure cross-flow triple-effect dividing wall tower distillation device for crude methanol refining, comprising a normal pressure dividing wall tower 1, a vacuum tower 2 and a pressure tower 3;

[0045] The atmospheric pressure dividing wall tower (a partition is provided on the upper part of the tower) is composed of a pre-tower (sub-tower) (total reflux) and an atmospheric pressure tower (mother tower), and is provided with an independent gas phase outlet respectively, while the lower part shares a space and a reboiler.

[0046] The raw material inlet of the pre-tower of the atmospheric bulkhead tower is connected to the upstream crude methanol, and the upstream crude methanol enters the raw material inlet of the pre-tower after being treated by the exhaust steam primary cooler 4 and the raw material preheater; the top gas phase outlet of the pre-tower is connected to the first vacuum tower reboiler 7, and the top gas phase is condensed in the first vacuum tower reboiler, and the light phase component is discharged as non-condensable gas, and the condensate is fully refluxed to the pre-tower;

[0047] The top gas phase of the atmospheric tower of the atmospheric bulkhead tower is connected to the reboiler 8 of the second vacuum tower. Part of the condensate flows back into the atmospheric tower, and the rest flows out to the outside as refined methanol product; the refined methanol extracted from the condensate after heat exchange in the reboiler of the second vacuum tower is the second methanol stream.

[0048] The liquid phase outlet of the atmospheric bulkhead tower is connected to the material inlet of vacuum tower 2. The inlet of the pressure tower is connected to the outlet of the vacuum tower, using 0.6 MPa live steam at 160°C as the heat source (Effect I). The light phase outlet at the top of the pressure tower is connected to the steam inlet of the atmospheric tower reboiler, serving as the heat source for the atmospheric tower reboiler (Effect II). Refined methanol is extracted from the condensate after heat exchange in the atmospheric tower reboiler, which becomes the first methanol stream.

[0049] The vacuum tower utilizes a dual reboiler, with the reboiler heat source utilizing secondary steam from the pre-tower overhead of the atmospheric bulkhead tower and the atmospheric tower overhead, respectively. This is known as the III effect. The light phase from the vacuum tower's overhead enters the vacuum tower condenser for processing, with a portion of the condensate flowing out as refined methanol product, forming the third methanol stream. The mother liquor from the vacuum tower's bottom is heated by heat exchange before entering the pressurization tower.

[0050] The outlet of the bottom of the pressurized tower is pure water, which is discharged after heat recovery, and fusel alcohol is discharged from the side line.

[0051] The top pressure of an atmospheric pressure bulkhead tower is 130-150 kPa (A), and the top temperature is 70°C-80°C. The pressure or temperature on both sides of the bulkhead tower (separated by a partition at the top) may vary slightly due to the influence of the top condenser, but keeping the difference as small as possible is beneficial to the operation of the bulkhead tower. Adjusting the cooling capacity of the reboiler adjusts the gas phase distribution to ensure that it is an atmospheric pressure tower.

[0052] The pressure at the top of the vacuum tower is 50-60 kPa (A), corresponding to a temperature of 48-52 ° C; the bottom temperature is 56-60 ° C;

[0053] The pressure at the top of the pressurized tower is 320-340 kPa (A), corresponding to a temperature of 96-100°C; the bottom temperature is 136-145°C. A represents absolute pressure.

[0054] As a preferred solution, the atmospheric pressure dividing wall tower can use industrial full countercurrent TST tower plates with larger gas-liquid flux, higher mass transfer efficiency and lower plate pressure drop.

[0055] As a preferred solution, the vacuum tower condenser 11 in the present invention is connected to a vacuum pump.

[0056] As a preferred solution, the vacuum tower adopts a packed tower, and its reboiler adopts a falling film reboiler, which can be equipped with a circulating pump.

[0057] As a preferred solution, the pressurized tower uses industrial full countercurrent TST tower plates with larger gas-liquid flux, higher mass transfer efficiency and lower plate pressure drop.

[0058] Example 1:

[0059] This embodiment is a low-pressure cross-flow three-effect bulkhead tower distillation process for refining crude methanol. The crude methanol is first preheated in the exhaust steam precooler 4 at the top of the vacuum tower 2 and then enters the raw material preheater 5 for secondary preheating. After preheating, the crude methanol temperature rises to about 75°C and enters one side of the atmospheric pressure bulkhead tower (pre-tower side) from the material inlet of the atmospheric pressure bulkhead tower. The top gas phase of the atmospheric pressure bulkhead tower enters the reboiler 7 of the first vacuum tower to provide heat and be condensed. The uncondensed light phase gas enters the light hydrocarbon condenser 9 for further condensation. The tail gas enters the spray absorption tower 10 to further recover methanol and then enter the subsequent combustion system. The condensate from the spray absorption tower 10 is fully refluxed into the atmospheric pressure bulkhead tower on the corresponding side. The top pressure of this side is 130 kPa(A) and the temperature is around 78°C. The top pressure on the other side of the atmospheric bulkhead tower (distillation side) is 130 kPa, and the top gas temperature is 71 ° C. The top gas on the other side of the atmospheric bulkhead tower enters the second vacuum tower reboiler 8, and the tail gas is heated and condensed. Part of the condensed condensate is refluxed into the atmospheric bulkhead tower 1 as the reflux liquid on the distillation side, and the other part is taken out as the vacuum tower refined methanol; the bottom temperature of the atmospheric bulkhead tower 1 is about 80 ° C; the heating steam of the atmospheric tower reboiler 6 comes from the top gas phase of the pressurized tower 3, and the gas phase temperature is about 100 ° C, that is, the heat transfer temperature difference of the atmospheric bulkhead tower reboiler is maintained at about 20 ° C.

[0060] Preferably, in order to ensure uniform gas distribution in the atmospheric pressure dividing wall tower, the pre-tower internals of the dividing wall tower adopt TST flow trays, and are equipped with a gas distribution device that matches the TST.

[0061] The bottom liquid of the atmospheric bulkhead tower 1 flows into the middle of the vacuum tower 2 via a pressure differential. The top pressure of the vacuum tower 2 is 60 kPa (A) and the temperature is 52°C. The top gas phase first enters the exhaust steam pre-cooler 4 to preheat the feedstock, and then enters the vacuum tower condenser 11. Part of the condensed liquid serves as reflux for the vacuum tower 2, while the remaining portion is withdrawn as refined methanol for the pressurized tower. The bottom temperature of the vacuum tower 2 is approximately 60°C. The heat transfer temperature difference of the first vacuum tower reboiler is approximately 18°C, and the heat transfer temperature difference of the second vacuum tower reboiler 8 is approximately 11°C.

[0062] Preferably, the internals of the vacuum tower are fillers; the reboiler of the first vacuum tower is a falling film reboiler;

[0063] The bottom liquid of the vacuum tower 2 enters the raw steam condensate preheater 12 through a pump, and enters the pressurizing tower 3 after preheating; the top pressure of the pressurizing tower 3 is 340 kPa (A) and the temperature is 100 ° C; the top gas phase of the pressurizing tower 3 enters the atmospheric pressure tower reboiler 6 of the atmospheric pressure dividing wall tower 1, and after condensation, part of the condensate is used as the reflux liquid of the pressurizing tower 3, and the other part is produced as the atmospheric pressure tower refined methanol; the bottom liquid temperature of the pressurizing tower 3 is about 141 ° C, and the discharge from the bottom of the pressurizing tower enters the raw material preheater 5 for cooling and then is discharged from the system as wastewater; the pressurizing tower reboiler 13 uses 600 kPa (A) raw steam as a heat source, and the steam temperature is 159 ° C, that is, the heat transfer temperature difference of the pressurizing tower reboiler 13 is maintained at 18 ° C; the side line of the pressurizing tower 3 produces fusel alcohol and is discharged from the system.

[0064] In this embodiment, the crude methanol content is 91.7%, the water content is 6.7%, and the operating parameters of each tower are shown in Table 1:

[0065]

[0066] The innovative connection mode of the tower equipment in the process of the present invention uses 600 kPa (A) raw steam as the heat source, which realizes the effective matching of the heat transfer temperature difference in each reboiler. It can achieve efficient operation in actual engineering while ensuring energy saving and consumption reduction. Each effect of the three-effect distillation in the present invention can operate normally, saving the floor space of the reboiler.

[0067] The present invention uses low-pressure raw steam, and the saturated steam temperature is constant, which can be almost evenly distributed to the three effects. The refined methanol content is controlled at above 99.98%, saving steam consumption.

[0068] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A low-pressure cross-flow triple-effect dividing wall tower distillation process for crude methanol refining, characterized in that: The process includes an atmospheric pressure bulkhead tower, a vacuum tower and a pressure tower, wherein the vacuum tower kettle is equipped with a first vacuum tower reboiler and a second vacuum tower reboiler, and the atmospheric pressure bulkhead tower kettle is equipped with an atmospheric pressure tower reboiler; The crude methanol is first preheated in the exhaust steam precooler at the top of the vacuum tower, and then enters the raw material preheater for secondary preheating. After preheating, the crude methanol temperature rises to 70-80°C. It then enters the atmospheric pressure bulkhead tower from the material inlet. The top gas phase on this side enters the reboiler of the first vacuum tower to provide heat and be condensed. The uncondensed light phase gas enters the light hydrocarbon condenser for further condensation, and the tail gas enters the spray absorption tower. The condensate from the spray absorption tower is fully refluxed into the atmospheric pressure bulkhead tower on the corresponding side. The top pressure of this side is 130-150KPa(A) and the top temperature is 70-80°C. The top pressure on the other side of the atmospheric bulkhead tower is 130-150 kPa(A), and the top gas temperature is 70-80°C. The top gas on this side enters the reboiler of the second vacuum tower, and part of the condensed condensate is refluxed into the atmospheric bulkhead tower as the reflux liquid on this side; the bottom temperature of the atmospheric bulkhead tower is 7-8°C higher than the top temperature; The inlet of the pressure tower is connected to the outlet of the vacuum tower kettle, and 0.6MPa raw steam is used as the heat source; the light phase outlet at the top of the tower is connected to the steam inlet of the atmospheric tower reboiler, which serves as the heat source of the atmospheric tower reboiler. Part of the condensate in the atmospheric tower reboiler flows back to the atmospheric tower, and the rest flows out to the outside as the refined methanol product; The outlet of the pressurized tower is pure water, which is discharged after heat recovery, and fusel alcohol is discharged from the side line; the top pressure of the pressurized tower is 320-340KPa (A), the top temperature is 96-100℃, and the bottom temperature is 136-140℃; The pressure at the top of the vacuum tower is 50-60 kPa (A), the temperature at the top is 48-52 ° C, and the temperature difference between the top and bottom of the vacuum tower is 7-8 ° C; The atmospheric tower reboiler, the vacuum tower top reflux, and the second vacuum tower reboiler all partially produce refined methanol.

2. The process according to claim 1, characterized in that The purity of methanol in the refined methanol is not less than 99.98 wt %.

3. The process according to claim 1, characterized in that The steam temperature of the raw steam is 155-165°C.

4. The process according to claim 1, characterized in that The crude methanol content is 80-93 wt%.

5. A low-pressure cross-flow triple-effect dividing wall tower distillation device for crude methanol refining, characterized in that: The device includes a normal pressure dividing wall tower, a vacuum tower and a pressure tower; The atmospheric pressure dividing wall tower is composed of a pre-tower and an atmospheric pressure tower. The upper parts of the pre-tower and the atmospheric pressure tower are separated by a partition. The pre-tower and the atmospheric pressure tower are respectively provided with independent gas phase outlets. The lower parts of the two towers share a space and a reboiler. The raw material inlet of the pre-tower of the atmospheric pressure dividing wall tower is connected to the upstream crude methanol; The top gas phase outlet of the pre-tower is connected to the reboiler of the first vacuum tower, which is respectively connected to the light hydrocarbon condenser, the kettle of the vacuum tower, and the raw steam condensate preheater; the outlet of the light hydrocarbon condenser is connected to the bottom inlet of the spray absorption tower, and the bottom outlet of the spray absorption tower is connected to the top reflux port of the pre-tower; light hydrocarbons are produced from the top of the spray absorption tower, and desalted water enters from the top of the spray absorption tower; The top gas phase of the atmospheric tower of the atmospheric bulkhead tower is connected to the reboiler of the second vacuum tower, and the reboiler of the second vacuum tower is installed in the kettle of the vacuum tower. Part of the condensate from the reboiler of the second vacuum tower flows back into the atmospheric tower, and part of it flows out to the outside as a refined methanol product; The liquid phase outlet of the tower bottom of the atmospheric pressure dividing wall tower is connected to the material inlet of the vacuum tower; the heat source of the atmospheric pressure tower reboiler of the atmospheric pressure dividing wall tower is provided by the top gas phase of the pressure tower; The top of the vacuum tower is connected to an exhaust steam primary cooler and a vacuum tower condenser; The outlet of the raw steam condensate preheater is connected to the material inlet of the pressurized tower, and the steam inlet of the raw steam condensate preheater is connected to the 0.6MPa industrial steam supply pipeline through the pressurized tower reboiler; The tower kettle of the pressure tower is equipped with a pressure tower reboiler, the top reflux port of the pressure tower is connected to the condensate outlet of the atmospheric tower reboiler, and the top gas phase outlet of the pressure tower is connected to the inlet of the atmospheric tower reboiler; the outlet of the pressure tower reboiler is also connected to the raw material preheater; The upstream crude methanol is connected to the raw material inlet of the pre-tower after passing through the exhaust steam primary cooler and the raw material preheater, and the waste water is produced in the raw material preheater; The atmospheric tower reboiler and the vacuum tower top reflux both produce refined methanol.

6. The device according to claim 5, characterized in that The atmospheric pressure dividing wall tower and the pressure tower adopt full countercurrent TST tower plates, the vacuum tower adopts a packed tower, and the reboiler of the first vacuum tower adopts a falling film reboiler.

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