CN113527058A - Side-line and bulkhead pre-rectifying tower heat trap multi-effect methanol rectifying method - Google Patents
Side-line and bulkhead pre-rectifying tower heat trap multi-effect methanol rectifying method Download PDFInfo
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Abstract
The invention discloses a multi-effect methanol rectification method of a side-track and bulkhead pre-rectifying tower heat trap, which is characterized in that energy matching is formed between towers by adjusting the working pressure and temperature of a pre-tower T1 and a pressurizing tower T3, so that the pre-tower T1 is used as the heat trap to form multi-effect rectification. Raw material crude methanol flows into a pre-tower T1, the steam at the top of the tower is partially condensed by a pre-tower condenser C1, and methanol oil and light component non-condensable gas are separated. The steam at the top of the atmospheric tower T2 partially refluxes after being condensed by an atmospheric tower condenser C2, and part of the steam is taken as a refined methanol product to flow out of a boundary region. The vapor at the top of the water tower T4 partially flows back after being condensed by a water tower condenser C3, and the other part is fusel liquid outlet boundary zone. The heat integration among different operating pressure towers is realized by utilizing the steam at the top of the rectifying tower, the consumption of external steam in the whole process is greatly reduced, and the equipment investment is reduced in the improved method.
Description
Technical Field
The invention belongs to the field of chemical separation processes, and particularly relates to a multi-effect methanol rectification method of a heat trap of a lateral line and bulkhead pre-rectifying tower.
Background
The methanol is the simplest saturated monohydric alcohol, has wide application, can be used for producing pesticides, sulfonamides and the like in the fields of pesticides and medicines, and can also be used as a raw material for producing formaldehyde to be used as a binding agent for wood processing. The currently commonly used methanol synthesis method takes coal as a source, and finally obtains a methanol product through gasification, low-temperature methanol washing, gas separation and methanol refining units.
The methanol rectification unit is used as a core unit for methanol refining, the energy consumption of the methanol rectification unit can account for 20% of the whole process flow, and the separation of target products and impurities is realized by inputting a large amount of energy, so that the methanol rectification unit is a typical energy-intensive process. The reduction of the energy consumption in the rectification process has important significance for optimizing the energy structure of the whole process. The traditional methanol separation process is a three-tower process, and the process has the characteristics of short process, convenience in start-up and the like. The process uses a pre-tower, a pressurizing tower and an atmospheric tower to separate methanol, the pre-tower separates methanol oil and light component gas, the pressurizing tower and the atmospheric tower simultaneously separate refined methanol at the top of the tower, and the side line and the bottom of the atmospheric tower respectively separate fusel oil and wastewater.
The partition wall tower is characterized in that a vertical partition wall is arranged in a rectifying tower, and the material flow in the tower is distributed according to the arrangement mode of the partition wall, so that the mass transfer and heat transfer processes are realized in one rectifying tower. The partition wall tower combines two rectifying towers together, so that the investment of the rectifying towers can be reduced, and the investment of a reboiler and a condenser can be saved. In addition, energy can be utilized in the partition wall tower, so that energy consumption is further saved.
The multi-effect rectification is to change the energy levels of different towers in a mode of gradually reducing the pressure of a plurality of towers. The former rectifying tower has high pressure and relatively high operation temperature, and the separated tower top steam can supply heat to the reboiler of the next low pressure tower to realize the purposes of steam condensation and liquid vaporization in the reboiler. Thus, the middle rectifying device can not be additionally provided with heat and cooling except for the rectifying towers at the two ends. After long-term use and research, the three-tower process develops double-effect rectification and other process methods based on feed division heat integration, light component division forward heat integration and light component division reverse heat integration. However, even if double-effect rectification is adopted, the steam consumption is 1.1 to 1.2 tons/methanol. The current production needs to continuously reduce the energy consumption of the methanol rectification process and improve the product quality. The traditional three-tower flow methanol rectification process has high energy consumption, the product can not meet the production requirement easily, the energy consumption can not be reduced well after the full development is achieved, and the recovery rate of the product gradually tends to the limit. Based on this, it is important to develop a new energy saving method.
Disclosure of Invention
The invention provides a multi-effect methanol rectification method of a heat trap of a lateral line and bulkhead pre-rectifying tower, aiming at solving the technical problem of the prior methanol rectification.
The technical scheme of the invention is as follows: a multi-effect methanol rectification method of a side line and bulkhead pre-rectifying tower heat trap is based on a rectification device comprising the following equipment: a pre-tower T1, a pre-tower first reboiler H1, a pre-tower second reboiler H2 and a pre-tower condenser C1; atmospheric tower T2, atmospheric tower condenser C2; pressurized column T3, pressurized column reboiler H3, pressurized column reflux drum V1; water tower T4, water tower reboiler H4, water tower condenser C3; wherein, the top steam pipeline of the pressurized tower T3 is connected with the pre-tower second reboiler H2; the rest reboilers are connected with steam pipelines with different pressures, and the condensers are connected with process cooling water pipelines.
The working pressure and temperature of the pre-tower T1 and the pressurized tower T3 are adjusted to form energy matching between the towers, so that the multi-effect rectification is formed by taking the pre-tower T1 as a heat trap.
(1) Raw material crude methanol flows into a pre-tower T1, the steam at the top of the tower is partially condensed by a pre-tower condenser C1, and methanol oil and light component non-condensable gas are separated. Part of the bottom stream of the pre-tower T1 flows into a first reboiler H1 of the pre-tower after being heated and vaporized by steam, and flows into the pre-tower T1, the reflux part of the other part of the stream flows into a second reboiler H2 of the pre-tower after being heated and vaporized by the top steam of the pressurized tower T3, and flows into the pre-tower T1, and the rest of the stream flows into the pressurized tower T3 for separation. The side stream of the pre-tower T1 enters an atmospheric tower T2 for separation;
(2) the steam at the top of the atmospheric tower T2 partially refluxes after being condensed by an atmospheric tower condenser C2, and part of the steam is taken as a refined methanol product to flow out of a boundary region. The bottom stream of the atmospheric tower T2 flows into a pre-tower T1 without passing through a reboiler;
(3) the reflux part of the bottom stream of the pressurized tower T3 flows into a pressurized tower reboiler H3, is vaporized by the heating part of steam and then flows into a pressurized tower T3, and the other part of the bottom stream is a wastewater outflow boundary area. The pressurized column T3 side draw portion is passed to water column T4 for separation.
(4) The vapor at the top of the water tower T4 partially flows back after being condensed by a water tower condenser C3, and the other part is fusel liquid outlet boundary zone. The reflux part of the bottom stream of the water tower T4 flows into a water tower reboiler H4 to be vaporized by steam heating, and the other part is a waste water discharge boundary zone.
Further, based on the multi-effect rectification and dividing wall column, the pre-column T1 and the atmospheric column T2 were combined into a dividing wall column T5; a first reboiler H5 of the dividing wall tower, a second reboiler H6 of the dividing wall tower, a first condenser C4 of the dividing wall tower and a second condenser C5 of the dividing wall tower respectively replace a first reboiler H1 of the pre-tower, a second reboiler H2 of the pre-tower, a condenser C1 of the pre-tower and a condenser C2 of the normal pressure tower; the steam at the top of the pressurized tower T3 is connected with a second reboiler H6 of a bulkhead tower, and after the condensed liquid is partially refluxed by a reflux tank, part of the condensed liquid is used as a refined methanol outflow boundary area.
Further, the four-column apparatus was changed to a five-column apparatus based on multi-effect rectification, and the medium-pressure column T6 and the high-pressure column T7 replaced the pressurized column T3; the top of the medium-pressure tower T6 is a medium-pressure tower reflux tank V2, and the bottom of the medium-pressure tower is a medium-pressure tower reboiler H8; the top of the high-pressure tower T7 is a high-pressure tower reflux tank V3, and the bottom of the high-pressure tower is a high-pressure tower reboiler H9; the pre-tower reboiler H7 replaces a pre-tower first reboiler H1 and a pre-tower second reboiler H2; the steam pipeline at the top of the medium-pressure tower T6 is connected with a pre-tower reboiler H7; the overhead vapor line of the higher pressure column T7 was connected to the medium pressure column reboiler H8.
The method is characterized in that the working pressure and temperature of a pre-tower T1 and a pressurized tower T3 are adjusted to form energy matching between the towers, so that the pre-tower T1 is used as a heat trap to form multi-effect rectification, and the method comprises the following steps:
(1) on the basis of a light component segmentation reverse heat integration four-tower process, crude methanol is separated by adopting a pre-tower T1, an atmospheric tower T2, a pressurized tower T3 and a water tower T4;
(2) by adjusting the operating pressures of the pre-column T1 and the pressurized column T3, heat matching between the rectification columns is achieved so that the pressurized column T3 overhead vapor just supplies heat to the pre-column second reboiler H2.
(3) Double-effect rectification is adopted between the pre-tower T1 and the pressurized tower T3, and the steam of the overhead stream of the pressurized tower T3 supplies heat to a second reboiler H2 of the pre-tower.
The operating pressure range of the pre-tower T1 is 130 kPa and 160kPa, and the reflux ratio is between 0.3 and 0.7; a pre-tower second reboiler H2 is arranged at the bottom of the pre-tower T1, and steam at the top of the pressurized tower T3 is used as a heat source;
the operating pressure range of the atmospheric tower T2 is 50-150kPa, and the reflux ratio is 1-2;
the operating pressure range of the pressurizing tower T3 is 300-400kPa, and the reflux ratio is between 2.5 and 4.5;
the water column T4 is operated at a pressure in the range of 50 to 150kPa with a reflux ratio in the range of 2 to 8.
Further, a five-tower device is changed into a four-tower device based on multi-effect rectification and a bulkhead tower, and a pre-tower T1 and an atmospheric tower T2 are combined into the bulkhead tower T5; the dividing wall column reboiler H11 replaces a pre-column reboiler H7; the steam pipeline at the top of the medium-pressure tower T6 is connected with a dividing wall tower reboiler H7;
advantageous effects
1. By the reverse double-effect rectification technology, heat integration among different operating pressure towers is realized by utilizing steam at the top of the rectification tower, and the consumption of external steam in the whole process is reduced to a greater extent.
2. The temperature and the pressure of the waste water are high, and the subsequent heat recovery can be facilitated.
3. In the improved process, the use of a divided wall column can further reduce equipment investment.
4. Is suitable for new devices and technical transformation.
Drawings
FIG. 1 is a schematic diagram of a multi-effect methanol rectification separation process based on a pre-rectifying tower as a heat trap;
FIG. 2 is a diagram of a modified multi-effect methanol rectification process using a pre-rectification column based on a dividing wall column as a heat trap;
FIG. 3 is a diagram of a methanol rectification separation flow based on five columns with a pre-rectification column as a hot trap;
FIG. 4 is a second diagram of a rectification separation flow of methanol based on five columns with a pre-rectification column as a hot trap;
FIG. 5 is a second diagram of a multi-effect methanol rectification improved flow scheme by using a pre-rectifying tower based on a bulkhead tower as a heat trap;
wherein: t1-pre-tower, H1-pre-tower first reboiler, H2-pre-tower second reboiler and C1-pre-tower condenser; t2-atmospheric tower, C2-atmospheric tower condenser; t3-pressurized column, H3-pressurized column reboiler, V1-pressurized column reflux drum; t4-water tower, H4-water tower reboiler, C3-water tower condenser; t5-bulkhead column, H5-bulkhead column first reboiler, H6-bulkhead column second reboiler, C4-bulkhead column first condenser, C5-bulkhead column second condenser; h7-pre-column reboiler; t6-medium pressure column, H8-medium pressure column reboiler, V2-medium pressure column reflux drum; t7-high pressure column, H9-high pressure column reboiler, V3-high pressure column reflux tank; h10-atmospheric tower reboiler; h11 — dividing wall column reboiler.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
example 1
As shown in fig. 1, a five-tower three-effect methanol rectification device based on a multi-effect rectification technology has the following connection modes: wherein, the overhead steam pipeline of the pressurized tower T3 is connected with the pre-tower second reboiler H2. The rest reboilers are connected with steam pipelines with different pressures, and the condensers are connected with process cooling water pipelines.
The invention adopts a reverse double-effect rectification technology, and the process flow comprises the following steps:
1) raw material crude methanol flows into a pre-tower T1, steam at the top of the tower is partially condensed by a pre-tower condenser C1, and methanol oil and light component non-condensable gas are separated; part of the bottom stream of the pre-tower T1 flows into a first reboiler H1 of the pre-tower after being heated and vaporized by steam, and flows into the pre-tower T1, the reflux part of the other part of the stream flows into a second reboiler H2 of the pre-tower after being heated and vaporized by the top steam of the pressurized tower T3, and flows into the pre-tower T1, and the rest of the stream flows into the pressurized tower T3 for separation; the side stream of the pre-tower T1 enters an atmospheric tower T2 for separation;
2) the steam at the top of the atmospheric tower T2 partially refluxes after being condensed by an atmospheric tower condenser C2, and part of the steam is used as a refined methanol product to flow out of a boundary region; the bottom stream of the atmospheric tower T2 flows into a pre-tower T1 without passing through a reboiler;
3) condensing the steam at the top of the pressurizing tower T3 into liquid through a second reboiler H2 of the pre-tower, refluxing a part of the liquid through a reflux tank V1 of the pressurizing tower, and taking the other part of the liquid as a refined methanol outflow boundary area; the effluent part of the bottom stream of the pressurizing tower T3 is a wastewater effluent boundary zone; the side stream from the pressurized column T3 is partially discharged into a water column T4 and separated; 4) the steam at the top of the water tower T4 is partially refluxed after being condensed by a water tower condenser C3, and the other part is a fusel outflow boundary zone; the effluent stream from the bottom of water column T4 is the effluent removal battery.
The whole-tower average operation pressure of the pre-tower T1 is 145kPa, and the reflux ratio is 0.3; the whole-tower average operation pressure of the atmospheric tower T2 is 100kPa, and the reflux ratio is 1; the whole-column average operating pressure of the pressurized column T3 was 350kPa, and the reflux ratio was 2.5; the overall column average operating pressure of the water column T4 was 100kPa with a reflux ratio of 2.
The steam consumption per monomer product of this process scheme is 0.86, which is about 28.33% lower than currently operating plants, compared to existing industrial processes.
Example 2
As shown in figure 2, the method for improving the flow of multi-effect methanol rectification by taking a pre-rectifying tower as a heat trap based on a dividing wall tower has the process flow basically consistent with that of the example 1. The dividing wall tower T5 replaces the pre-tower T1 and the atmospheric tower T2 in the example 1; the first reboiler H5 of the dividing wall tower, the second reboiler H6 of the dividing wall tower, the first condenser C4 of the dividing wall tower and the second condenser C5 of the dividing wall tower respectively replace the first reboiler H1 of the pre-tower, the second reboiler H2 of the pre-tower, the condenser C1 of the pre-tower and the condenser C2 of the normal pressure tower; and the steam at the top of the pressurized tower T3 is connected with a second reboiler H6 of a dividing wall tower, and the condensed liquid flows out of a boundary area as a refined methanol product. The remaining flow charts show the connection method in accordance with case 1.
The total column average operating pressure of the divided wall column T5 was 135kPa, the reflux ratio was 0.3 and 1; the whole-column average operating pressure of the pressurized column T3 was 350kPa, and the reflux ratio was 2.5; the overall column average operating pressure of the water column T4 was 100kPa with a reflux ratio of 2.
The steam consumption per monomer product of this process scheme is 0.86, which is about 28.33% lower than currently operating plants, compared to existing industrial processes.
Example 3
As shown in fig. 3, a first method of a multi-effect methanol rectification improved flow based on five towers and using a pre-rectification tower as a heat trap has a process flow idea basically consistent with that of example 1. The medium-pressure column T6 and the high-pressure column T7 replace the pressurized column T3 in example 1; the top of the medium-pressure tower T6 is a medium-pressure tower reflux tank V2, and the bottom of the medium-pressure tower is a medium-pressure tower reboiler H8; the top of the high-pressure tower T7 is a high-pressure tower reflux tank V3, and the bottom of the high-pressure tower is a high-pressure tower reboiler H9; the pre-tower reboiler H7 replaces the pre-tower first reboiler H1 and the pre-tower second reboiler H2 in the embodiment 1; the reflux part of the bottom stream of the pre-tower T1 flows into a pre-tower reboiler H7, is heated and vaporized by the top steam of the intermediate pressure tower T6 and then flows into a pre-tower T1, and the other part of the stream flows into the intermediate pressure tower T6 for separation; after steam at the top of the medium pressure tower T6 is condensed into liquid by a pre-tower reboiler H7, part of the liquid flows back through a medium pressure tower reflux tank V2, and the other part of the liquid flows out of a boundary area as refined methanol; the reflux part of the bottom stream of the medium-pressure tower T6 flows into the medium-pressure tower T6 after being heated and vaporized by the top steam of the high-pressure tower T7, and the other part flows into the high-pressure tower T7 for separation; the steam at the top of the high-pressure tower T7 flows into a medium-pressure tower reboiler H8 to be condensed into liquid, and after partial reflux of the liquid flows through a high-pressure tower reflux tank V3, the other part of the liquid flows out of a boundary area for refined methanol; the bottom liquid reflux part of the high-pressure tower flows into the high-pressure tower T7 after being heated and vaporized by steam, and the other part of the bottom liquid reflux part of the high-pressure tower flows into a water tower reboiler H4 to recover waste heat and then flows out of a boundary region as waste water; the side stream discharged from the high pressure tower T7 flows into a water tower T4 for separation; the steam at the top of the water tower T4 is partially refluxed after being condensed by a water tower condenser C3, and the other part is a refined methanol outflow boundary zone; the bottom stream flowing out of the water tower T4 is fusel removing battery limit. The remaining flow charts show the connection method in accordance with case 1.
The whole-tower average operation pressure of the pre-tower T1 is 150kPa, and the reflux ratio is 0.3; the whole-tower average operation pressure of the atmospheric tower T2 is 100kPa, and the reflux ratio is 1; the whole-tower average operation pressure of the medium-pressure tower T6 is 250kPa, and the reflux ratio is 1.5; the average operating pressure of the whole high-pressure tower T7 is 700kPa, and the reflux ratio is 3; the overall column average operating pressure of the water column T4 was 100kPa with a reflux ratio of 2.
The steam consumption per unit of monomer product of this process scheme is 0.6 compared to the existing industrial process, which is about 50% lower than the currently operating plant.
Example 4
As shown in fig. 4, a second method based on five towers and using a pre-rectifying tower as a heat trap for rectifying the multi-effect methanol has a process flow which is basically consistent with that of the example 3. An atmospheric tower reboiler H10 is added at the bottom of the atmospheric tower T2; the water tower T4 eliminates a reboiler at the bottom of the tower; the reflux part of the bottom stream of the pre-tower T1 flows into a pre-tower reboiler H7, the reflux part is heated and vaporized by partial steam at the top of the intermediate pressure tower T6 and then flows into a pre-tower T1, and the other part of the stream flows into an atmospheric tower T2 for separation; the reflux part of the bottom stream of the atmospheric tower T2 is heated and vaporized by the other part of steam at the top of the medium-pressure tower T6 and then flows into the atmospheric tower T2, and the other part of the stream flows into the medium-pressure tower T6 for separation; the steam at the top of the medium pressure tower T6 respectively flows into a pre-tower reboiler H7 and an atmospheric tower reboiler H10 to be condensed into liquid and collected, part of the liquid flows back through a medium pressure tower reflux tank V2, and the other part of the liquid is used as a refined methanol outflow boundary area; the bottom stream of the water tower T4 flows into a high pressure tower T7 for separation without passing through a reboiler; the overhead vapor of the water tower partially flows back through a water tower condenser C3, and part of the overhead vapor of the water tower is used as the fusel to flow out of the critical zone. The remaining flow charts show the connection method in accordance with case 3.
The whole-tower average operation pressure of the pre-tower T1 is 150kPa, and the reflux ratio is 0.4; the whole-tower average operation pressure of the atmospheric tower T2 is 100kPa, and the reflux ratio is 1; the average operation pressure of the whole medium-pressure tower T6 is 250kPa, and the reflux ratio is 2; the average operating pressure of the whole high-pressure tower T7 is 700kPa, and the reflux ratio is 4; the overall column average operating pressure of the water column T4 was 100kPa with a reflux ratio of 3.
The steam consumption per unit of monomer product of this process scheme is 0.6 compared to the existing industrial process, which is about 50% lower than the currently operating plant.
Example 5
As shown in figure 5, the technological process of the multi-effect methanol rectification improved process based on the dividing wall tower and using the pre-rectifying tower as the heat trap is basically consistent with the process of the embodiment 3. The dividing wall tower T5 replaces the pre-tower T1 and the atmospheric tower T2 in the example 3; the dividing wall column reboiler H11 replaces the pre-column reboiler H7 in example 3; the first condenser C4 of the dividing wall tower and the second condenser C5 of the dividing wall tower respectively replace a pre-tower condenser C1 and an atmospheric tower condenser C2; the water tower T4 eliminates a reboiler at the bottom of the tower; the reflux part of the bottom stream of the dividing wall column T5 flows into a dividing wall column reboiler H11, the bottom stream is heated and vaporized by the top steam of the intermediate pressure column T6 and then flows into a dividing wall column T5, and the other part of the stream flows into the intermediate pressure column T6 for separation; after steam at the top of the medium pressure tower T6 is condensed into liquid by a partition tower reboiler H11, part of the liquid flows back through a medium pressure tower reflux tank V2, and the other part of the liquid flows out of a boundary area as refined methanol; the bottom stream of the water tower T4 flows into a high pressure tower T7 for separation without passing through a reboiler; the overhead vapor of the water tower partially flows back through a water tower condenser C3, and part of the overhead vapor of the water tower is used as the fusel to flow out of the critical zone. The remaining flow charts show the connection method in accordance with case 3.
The total column average operating pressure of the divided wall column T5 was 135kPa, the reflux ratio was 0.3 and 1; the whole-tower average operation pressure of the medium-pressure tower T6 is 250kPa, and the reflux ratio is 1.5; the average operating pressure of the whole high-pressure tower T7 is 700kPa, and the reflux ratio is 3; the overall column average operating pressure of the water column T4 was 100kPa with a reflux ratio of 2.
The steam consumption per unit of monomer product of this process scheme is 0.6 compared to the existing industrial process, which is about 50% lower than the currently operating plant.
Claims (5)
1. The multi-effect methanol rectification method of the heat trap of the side line and bulkhead pre-rectifying tower is characterized in that the multi-effect methanol rectification device based on the pre-rectifying tower as the heat trap comprises the following equipment:
a pre-tower (T1), a pre-tower first reboiler (H1), a pre-tower second reboiler (H2) and a pre-tower condenser (C1);
atmospheric tower (T2), atmospheric tower condenser (C2);
a pressurized column (T3), a pressurized column reboiler (H3), a pressurized column reflux drum (V1);
water column (T4), water column reboiler (H4), water column condenser (C3);
wherein, the top steam pipeline of the pressurized tower (T3) is connected with a second reboiler (H2) of the pre-tower;
1) raw material crude methanol flows into a pre-tower (T1), the steam at the top of the tower is partially condensed by a pre-tower condenser (C1), and methanol oil and light component non-condensable gas are separated; part of the bottom stream of the pre-tower (T1) flows into a first reboiler (H1) of the pre-tower after being heated and vaporized by steam, and flows into the pre-tower (T1), the reflux part of the other part of the stream flows into a second reboiler (H2) of the pre-tower, and flows into the pre-tower (T1) after being heated and vaporized by the steam at the top of the pressurizing tower (T3), and the rest part of the stream flows into the pressurizing tower (T3) for separation;
2) the side stream of the pre-tower (T1) enters an atmospheric tower (T2) for separation;
3) the steam at the top of the atmospheric tower (T2) is partially refluxed after being condensed by an atmospheric tower condenser (C2), and part of the steam is used as a refined methanol product to flow out of a boundary region; the bottom stream of the atmospheric column (T2) flows into the pre-column (T1) without passing through a reboiler;
4) condensing the tower top steam of the pressurizing tower (T3) into liquid by a second reboiler (H2) of the pre-tower, partially refluxing the liquid by a pressurizing tower reflux tank (V1), and taking part of the liquid as a refined methanol outflow boundary region;
the reflux part of the bottom stream of the pressurized tower (T3) flows into a reboiler (H3) of the pressurized tower, is vaporized by the heating part of steam and then flows into the pressurized tower (T3), and the other part of the bottom stream is a wastewater outflow boundary region;
the side stream from the pressurized column (T3) is partially fed into a water column (T4) for separation;
5) the overhead vapor of the water tower (T4) is partially refluxed after being condensed by a water tower condenser (C3), and the other part is fusel outflow boundary zone;
the reflux part of the bottom stream of the water tower (T4) flows into a reboiler (H4) of the water tower to be heated and vaporized by steam, and the other part is a waste water discharge boundary zone.
2. The multi-effect methanol rectification method of the side line and bulkhead pre-rectifying tower heat trap is characterized in that,
1) combining a preliminary column (T1) and an atmospheric column (T2) into a divided wall column (T5) based on a multi-effect rectification and divided wall column;
2) a first reboiler (H5) of a dividing wall tower, a second reboiler (H6) of the dividing wall tower, a first condenser (C4) of the dividing wall tower and a second condenser (C5) of the dividing wall tower are respectively used for replacing a first reboiler (H1) of a pre-tower, a second reboiler (H2) of the pre-tower, a condenser (C1) of the pre-tower and a condenser (C2) of a normal pressure tower;
3) the steam at the top of the pressurized tower (T3) is connected with a second reboiler (H6) of the dividing wall tower, and after the condensed liquid is partially refluxed by a reflux tank, part of the condensed liquid is taken as refined methanol to flow out of a boundary region.
3. The multi-effect methanol rectification method of the side line and bulkhead pre-rectifying tower heat trap is characterized in that,
1) changing a four-tower device into a five-tower device based on multi-effect rectification, wherein a medium-pressure tower (T6) and a high-pressure tower (T7) replace a pressurized tower (T3);
2) the top of the medium-pressure tower (T6) is provided with a medium-pressure tower reflux tank (V2), and the bottom of the medium-pressure tower reboiler (H8);
3) the top of the high-pressure tower (T7) is a high-pressure tower reflux tank (V3), and the bottom of the high-pressure tower (T7) is a high-pressure tower reboiler (H9);
4) the pre-tower reboiler (H7) replaces a pre-tower first reboiler (H1) and a pre-tower second reboiler (H2);
5) the overhead steam pipeline of the medium-pressure tower (T6) is connected with a pre-tower reboiler (H7);
6) the high pressure column (T7) overhead vapor line was connected to a medium pressure column reboiler (H8).
4. The multi-effect methanol rectification method of the side line and bulkhead pre-rectifying tower heat trap is characterized in that,
1) combining a preliminary column (T1) and an atmospheric column (T2) into a divided wall column (T5) based on a multi-effect rectification and divided wall column;
2) a dividing wall column reboiler (H11) replaces the pre-column reboiler (H7).
3) The medium pressure column (T6) overhead vapor line was connected to a dividing wall column reboiler (H11).
5. The method for rectifying multi-effect methanol by using a side-draw and bulkhead pre-rectifying tower heat trap is characterized in that the pre-tower (T1) is used as a heat trap to form multi-effect rectification by adjusting the working pressure and the working temperature of the pre-tower (T1) and a pressurized tower (T3) to form energy matching between the towers, and the method comprises the following steps:
1) on the basis of a light component segmentation reverse heat integration four-tower flow, a pre-tower (T1), an atmospheric tower (T2), a pressurized tower (T3) and a water tower (T4) are adopted to separate crude methanol;
2) the heat matching between the rectifying columns is realized by adjusting the operating pressure of the pre-tower (T1) and the pressurized tower (T3), so that the steam at the top of the pressurized tower (T3) just supplies heat to a second reboiler (H2) of the pre-tower;
3) double-effect rectification is adopted between the pre-tower (T1) and the pressurized tower (T3), and the steam of the overhead stream of the pressurized tower (T3) supplies heat to a second reboiler (H2) of the pre-tower;
the operating pressure range of the pre-tower (T1) is 130-160kPa, and the reflux ratio is 0.3-0.7; a pre-tower second reboiler (H2) is arranged at the bottom of the pre-tower (T1), and the steam at the top of the pressurized tower (T3) is used as a heat source;
the operating pressure range of the atmospheric tower (T2) is 50-150kPa, and the reflux ratio is 1-2;
the operating pressure range of the pressurizing tower (T3) is 300-400kPa, and the reflux ratio is between 2.5 and 4.5;
the water column (T4) is operated at a pressure in the range of 50 to 150kPa with a reflux ratio in the range of 2 to 8.
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