An energy-saving system integrating multi-effect distillation and low-pressure-drop distillation tower

Abstract

The invention discloses a kind of energy-saving system of multiple-effect distillation integration with low-pressure drop rectifying tower, including parachlorine tower, adjacent chlorine tower, parachlorine tower is equipped with the first reboiler, and adjacent chlorine tower is equipped with the second reboiler;The middle part of parachlorine tower is respectively provided with the first feed opening, the second feed opening, parachlorine tower reactor is provided with discharge pipeline, and discharge pipeline is provided with heat exchanger, and feed pipeline is connected with the first feed opening through heat exchanger;Parachlorine tower top gas outlet is respectively connected with the reflux port of parachlorine tower, adjacent chlorine tower through the second reboiler;Adjacent chlorine tower is provided with the 3rd feed opening, the 4th feed opening, adjacent chlorine tower top gas outlet is connected with the first condenser, the second condenser in sequence, and the feed pipeline of adjacent chlorine tower is connected with the 3rd feed opening through the first condenser;Adjacent chlorine tower reactor discharge port is connected with the second feed opening of parachlorine tower.The present invention system effectively reduces the pressure drop of rectifying tower, realizes the low-energy consumption smart separation of mixed ortho / parachlorotoluene system.

Description

Technical Field

[0001] The present invention belongs to the field of chemical separation and relates to an energy-saving system integrating a multi-effect distillation and a low-pressure-drop distillation tower, and more particularly to an energy-saving system integrating a multi-effect distillation and a low-pressure-drop distillation tower for a mixed o-chlorotoluene / p-chlorotoluene system having a small boiling point difference and being difficult to separate. Background Art

[0002] Distillation is a separation process that uses the different volatilities of the components in a mixture to separate each other. It is widely used in industrial production such as petroleum, chemical industry, and light industry for the purification of raw materials, refining of products, and some post-processing processes.

[0003] In industrial production processes, it is often encountered that the boiling point difference in the separation system is small. When using distillation separation, an extremely high number of separation theoretical plates and a high reflux ratio are required, resulting in high equipment manufacturing costs and separation energy consumption, and high product production costs.

[0004] For the ortho-chlorotoluene / para-chlorotoluene system produced by chlorination on the toluene ring, since the boiling point difference between ortho-chlorotoluene and para-chlorotoluene is only 3 ° C, if separation is to be achieved, the theoretical plate number of the distillation separation is required to be ≥155, and the distillation tower is ≥50 meters, resulting in a very large energy consumption of the distillation separation method. Patent application CN116003213A discloses a separation method for a toluene chlorination product waste liquid. Under a reduced pressure condition of 35-45kPa at the top pressure of the tower, ortho-chlorotoluene and para-chlorotoluene are distilled and separated. The number of plates in the ortho-chlorotoluene distillation separation tower is 155, and the top reflux ratio of the distilled ortho-chlorotoluene is greater than 60, and the ortho-chlorotoluene purity obtained at the top of the tower is 98.2wt%. Direct distillation has the disadvantages of large single tower height and reflux ratio, and high energy consumption. Patent CN101497552A splits the ortho-chlorotoluene tower into two towers connected in series, reducing the height of the single tower, but does not change the disadvantage of high energy consumption. Patent application CN105693465A splits the chlorotoluene isomer distillation system into an o-chlorotoluene tower and a p-chlorotoluene tower, and divides the conventional distillation tower into a low-pressure tower and a high-pressure tower. By adjusting the pressure difference between the two towers, the gas from the high-pressure tower top is used as a heat source for the low-pressure tower kettle reboiler, thereby achieving heat coupling and matching utilization, which can reduce total energy consumption by 30% to 40%. This method sets the chlorotoluene material feed position in the low-pressure tower. At the same time, the low-pressure tower kettle needs to use an auxiliary reboiler to compensate for the energy shortage of the main reboiler. Since both the high-pressure tower and the low-pressure tower require additional auxiliary reboilers, it shows that there are still defects in the comprehensive utilization of energy. Patent application CN109134189A discloses a mixed chlorotoluene MVR distillation system. The o-chlorotoluene vapor at the top of the o-chlorotoluene tower exchanges heat with liquid water, and the liquid water absorbs the latent heat released by the condensation of the o-chlorotoluene vapor and converts it into water vapor. After being compressed by a compressor, it is used as a heat source to heat the distillation tower kettle, achieving comprehensive energy utilization. The main drawback of this method is that water vapor can only be used as a heat source for the bottom of the tower after it has been heated and pressurized at a certain compression ratio. Moreover, since the evaporation pressures of the three towers in series are different, the steam pressures required by the distillation bottom are also different. Therefore, the compression ratio needs to be set based on the maximum evaporation pressure. The compression ratio is often large, and the larger the compression ratio, the higher the electricity consumption.

[0005] In the aforementioned distillation system, the comprehensive energy utilization between distillation towers depends on the distillation pressure differential between the towers. However, when using conventional distillation towers to distill difficult-to-separate systems, the high theoretical plate number and height of the distillation towers often result in a distillation pressure drop of up to 15-25 kPa in actual applications, resulting in an excessively high temperature difference between the tower top and the bottom. If the distillation pressure differential between series distillation towers is used to reduce the energy consumption of series distillation, the energy demand caused by the increased pressure drop in the series distillation towers can only be overcome by increasing the distillation pressure of the first tower. However, the increased distillation pressure also leads to increased distillation energy consumption. Summary of the Invention

[0006] The present invention aims to address the problems existing in the series distillation process of difficult-to-separate systems such as mixed o- / p-chlorotoluene, and proposes a multi-effect distillation energy-saving system for difficult-to-separate systems. The system integrates a multi-effect distillation method with a low-pressure drop distillation tower into a new distillation system to achieve low-energy distillation separation of difficult-to-separate mixed o- / p-chlorotoluene systems.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] An energy-saving system integrating a multi-effect distillation and a low-pressure-drop distillation tower comprises a para-chlorine tower 1 and an ortho-chlorine tower 2. The para-chlorine tower 1 kettle is equipped with a first reboiler 3, and the ortho-chlorine tower 2 kettle is equipped with a second reboiler 4. The para-chlorine tower 1 is provided with a first feed port for feeding a mixed ortho-chlorotoluene raw material and a second feed port for feeding the ortho-chlorine tower kettle material. The para-chlorine tower 1 kettle is provided with a discharge pipeline for extracting the para-chlorotoluene product. The discharge pipeline is provided with a heat exchanger 5. The feed pipeline is connected to the first feed port via the heat exchanger 5 so that the mixed ortho-chlorotoluene raw material to be fed into the para-chlorine tower is heat-exchanged with the para-chlorine tower kettle material. The top gas outlet of the para-chlorine tower 1 is connected to the top reflux port of the para-chlorine tower and the fourth feed port of the ortho-chlorine tower 2 via the second reboiler 4. The gas phase material discharged from the top of the para-chlorine tower enters the second reboiler as a heat source. 4 and the adjacent chloro tower kettle material indirect heat exchange, the gaseous phase material is changed into the liquid phase material, a part of the liquid phase material enters the middle part of the adjacent chloro tower, and the remaining liquid phase materials are returned to the top of the chloro tower; Described adjacent chloro tower is provided with the 3rd feed opening for mixed adjacent / para-chlorotoluene raw material feeding, the 4th feed opening for feeding the chloro tower overhead material, the adjacent chloro tower 2 top gas outlet is connected with the first condenser 6 and the second condenser 7 in sequence, the outlet of the second condenser 7 is provided with two pipelines, wherein one pipeline is connected with the top reflux port of the adjacent chloro tower, and the other pipeline is used to extract the adjacent chlorotoluene product; The feed line of adjacent chloro tower 2 is connected with the 3rd feed opening through the first condenser 6, and the mixed adjacent / para-chlorotoluene raw material enters adjacent chloro tower 2 after the heat exchange of the gaseous phase material discharged with the adjacent chloro tower overhead in the condenser; Described adjacent chloro tower 2 tower reactor discharge port is connected with the second feed opening of chloro tower 1.

[0009] The chlorine tower 1 is a multi-channel distillation tower with multiple channels arranged in parallel. The cross-sectional area of ​​each channel is 5 to 13 cm. 2 , each channel is filled with high-efficiency fillers; the gas-liquid flow rate in each channel remains uniform, the amount of fillers filled in each channel remains consistent, and the reflux liquid spray density at the top of each channel remains consistent.

[0010] The ortho-chlorine tower 2 is a multi-channel distillation tower with multiple channels arranged in parallel. The cross-sectional area of ​​each channel is 5 to 13 cm. 2, each channel is filled with high-efficiency fillers; the gas-liquid flow rate in each channel remains uniform, the amount of fillers filled in each channel remains consistent, and the reflux liquid spray density at the top of each channel remains consistent.

[0011] The theoretical plate number of the high-efficiency filler is 50 to 80 pieces / m, which is much larger than the theoretical plate number of commonly used industrial fillers (2 to 5 pieces / m).

[0012] Specifically, the high-efficiency filler can be a triangular spiral filler, a θ-ring wire mesh filler or a spiral spring wire filler.

[0013] In the para-chlorine tower, the packing height is 1.5 to 3 meters; in the ortho-chlorine tower, the packing height is 1.5 to 3 meters.

[0014] In the para-chloro tower, the first feed port is higher than the second feed port, that is, the feed position of the mixed o- / p-chlorotoluene raw material is higher than the position where the o-chloro tower kettle material enters the para-chloro tower.

[0015] Preferably, the first feed inlet is 25 to 30 theoretical plate heights higher than the second feed inlet.

[0016] Preferably, the top gas outlet of the para-chlorine tower 1 is connected to the heating medium inlet of the second reboiler 4, and the heating medium outlet of the second reboiler 4 is provided with two pipelines, one of which is connected to the top reflux port of the para-chlorine tower, and the other is connected to the fourth feed port of the ortho-chlorine tower 2.

[0017] In the ortho-chlorotoluene tower, the fourth feed port is higher than or equal to the third feed port, that is, the position where the liquid material converted from the gaseous material discharged from the top of the para-chlorotoluene tower enters the ortho-chlorotoluene tower is higher than or equal to the feed position of the mixed ortho- / para-chlorotoluene raw material.

[0018] Preferably, when the fourth feed port is higher than the third feed port, the fourth feed port is 25 to 30 theoretical plate heights higher than the third feed port.

[0019] The first reboiler 3 uses fresh steam as a heat source to heat the chlorine tower kettle material.

[0020] Another object of the present invention is to provide a method for separating para-chlorotoluene and o-chlorotoluene based on an energy-saving system integrating the multi-effect distillation and the low pressure drop distillation tower, comprising:

[0021] Para-chlorine tower 1 and ortho-chlorine tower 3 are fed simultaneously;

[0022] The mixed o- / p-chlorotoluene feedstock enters the heat exchanger 5, where the p-chlorotoluene product extracted from the p-chlorotoluene tower 1 is heated, and then enters the p-chlorotoluene tower 1; the gaseous material discharged from the top of the p-chlorotoluene tower 1 enters the second reboiler 5 as a heat source, and indirectly exchanges heat with the bottom material of the o-chlorotoluene tower 2. After phase change, it is converted into a liquid-phase material, part of which enters the middle of the o-chlorotoluene tower 2, and the remaining material returns to the p-chlorotoluene tower 1 from the top; the bottom material of the p-chlorotoluene tower 1 and the mixed o- / p-chlorotoluene feedstock to be entered into the p-chlorotoluene tower 1 are heat-exchanged in the heat exchanger 5 and extracted as the p-chlorotoluene product;

[0023] The mixed o- / p-chlorotoluene feedstock enters the first condenser 6, exchanges heat with the gaseous material discharged from the top of the o-chloro tower 2, and then enters the o-chloro tower 2; the o-chloro tower kettle material enters the p-chloro tower from the second feed inlet; the gaseous material discharged from the top of the o-chloro tower 2 enters the first condenser 6, exchanges heat with the mixed o- / p-chlorotoluene feedstock to be entered into the o-chloro tower 2, and then enters the second condenser 7 to be further cooled into a liquid material. Part of the liquid material returns to the o-chloro tower 2 from the top of the tower, and the remaining liquid material is used as the o-chlorotoluene product.

[0024] In the mixed o-chlorotoluene / para-chlorotoluene raw material, the mass fraction of o-chlorotoluene is 45-55wt%, and the rest is para-chlorotoluene; and the temperature of the mixed o-chlorotoluene / para-chlorotoluene raw material is room temperature.

[0025] The mass flow ratio of the mixed o- / p-chlorotoluene raw material entering the o-chloro tower to the mixed o- / p-chlorotoluene raw material entering the p-chloro tower is 1:1 to 1:1.5.

[0026] The mixed o-chlorotoluene / p-chlorotoluene raw material enters the heat exchanger 5 and is preheated to 80-110° C. by the p-chlorotoluene product extracted from the p-chlorotoluene tower.

[0027] The top pressure of the parachlorine tower is 20-30 kPa (absolute pressure), the top temperature is 104-110° C., the bottom pressure is 21-35 kPa (absolute pressure), the bottom temperature is 112-118° C., and the pressure drop of the parachlorine tower is 0.5-5 kPa.

[0028] The gaseous material discharged from the top of the para-chlorotoluene tower contains 55-75 wt% of o-chlorotoluene and the remainder is para-chlorotoluene.

[0029] The gaseous material discharged from the top of the para-chlorine tower enters the second reboiler as a heat source, exchanges heat with the material in the kettle of the ortho-chlorine tower, and is converted into liquid material through phase change. The liquid material is divided into two streams, and the material accounting for 8 to 13 wt% of the total liquid material enters the middle part of the ortho-chlorine tower, and the rest of the material returns to the top of the para-chlorine tower.

[0030] The mixed o- / p-chlorotoluene raw material enters the first condenser and is preheated to 45-55° C. by the gaseous material discharged from the top of the o-chlorotoluene tower.

[0031] The tower top pressure of the adjacent chlorine tower is 5-10kPa (absolute pressure), the tower top temperature is 65-75°C, the tower bottom pressure is 6.5-13kPa, the tower bottom temperature is 80-100°C, the pressure drop of the adjacent chlorine tower is 0.5-5kPa, and the reflux ratio is 12-15.

[0032] In the o-chlorotoluene kettle material, the content of o-chlorotoluene is 25-45wt%, and the rest is p-chlorotoluene (that is, the content of p-chlorotoluene is 55-75%).

[0033] The mass fraction of p-chlorotoluene in the p-chlorotoluene product is above 99.5 wt %; the mass fraction of o-chlorotoluene in the o-chlorotoluene product is above 99.5 wt %.

[0034] Since the o-chlorotoluene content in the overhead gas phase of the para-chlorotoluene tower is 55-75 wt%, with the remainder being para-chlorotoluene, the o-chlorotoluene content need not reach 99.5%. Meanwhile, the para-chlorotoluene content in the bottom discharge of the o-chlorotoluene tower is 55-75 wt%, with the remainder being o-chlorotoluene, and the para-chlorotoluene content also need not reach 99.5%. Therefore, during distillation separation, the separation degrees in both distillation towers are relatively low, requiring a relatively small number of theoretical plates. Using high-efficiency packing greatly reduces the tower height, thereby significantly reducing the pressure drop within the towers.

[0035] The present invention is beneficial in that:

[0036] The energy-saving system combining the multi-effect distillation with the low-pressure-drop distillation tower of the present invention can avoid the high-pressure-drop disadvantage that a high tower will inevitably produce, effectively reduce the pressure drop of the distillation tower, and reduce the bottom pressure of the distillation tower, thereby reducing the energy consumption of distillation.

[0037] 2 Compared with the existing multi-tower series MVR distillation technology, the present invention avoids the use of MVR dynamic equipment, reducing equipment investment and power consumption.

[0038] 3. The energy-saving system of the present invention combines multiple-effect distillation with a low-pressure-drop distillation tower. Due to the use of a low-pressure-drop distillation tower, the temperature difference between the tower top and the tower bottom is small. It is particularly suitable for systems with a small difference in boiling points and achieves low-energy distillation separation of mixed o- / p-chlorotoluene systems.

[0039] 4. The para-chlorotoluene tower and the ortho-chlorotoluene tower of the present invention are connected in series in form, but are fed into the para-chlorotoluene tower and the ortho-chlorotoluene tower respectively and are connected in parallel in operation. Such a form makes it possible to almost completely utilize the heat of the para-chlorotoluene tower kettle discharge, and simultaneously the raw materials entering the para-chlorotoluene tower can be preheated to the expected temperature, thereby reducing the operating energy consumption of the tower; whereas the operating form of the single tower is such that the mass fraction of para-chlorotoluene and ortho-chlorotoluene in the raw materials is almost the same, and therefore, the feed flow rate is inevitably larger than the discharge amount. Although heat can also be utilized, the amount of the feed and discharge differs too much (difference of 1 times), and the temperature of the raw materials cannot be raised to the expected temperature, thereby increasing the operating energy consumption of the tower.

[0040] 5. By operating two towers in series and controlling the composition of the para-chlorine tower overhead, the para-chlorine tower's reflux ratio can be significantly reduced. The reflux ratio is directly related to the distillation tower's steam consumption. Simultaneously, controlling the composition of the ortho-chlorine tower's bottom material can significantly reduce the ortho-chlorine tower's steam consumption. Consequently, the fresh steam consumption of the entire system can be significantly reduced, achieving energy conservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of an energy-saving system integrating multi-effect distillation and a low-pressure-drop distillation tower.

[0042] Figure 1 Among them, 1-para-chlorine tower, 2-ortho-chlorine tower, 3-first reboiler, 4-second reboiler, 5-heat exchanger, 6-first condenser, 7-second condenser. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0044] Example 1

[0045] like Figure 1As shown, an energy-saving system integrating multi-effect distillation and low-pressure drop distillation towers comprises a para-chlorine tower 1 and an ortho-chlorine tower 2. The para-chlorine tower 1 kettle is equipped with a first reboiler 3, which uses fresh steam as a heat source to heat the para-chlorine tower kettle material. The ortho-chlorine tower 2 kettle is equipped with a second reboiler 4. The para-chlorine tower 1 is provided with a first feed port for feeding a mixed ortho-chlorotoluene raw material and a second feed port for feeding the ortho-chlorine tower kettle material. A heat exchanger 5 is provided on the feed pipeline. The para-chlorine tower 1 kettle is provided with a discharge pipeline for extracting the para-chlorotoluene product. The discharge pipeline is coupled to the heat exchanger 5 so that the para-chlorine tower kettle material exchanges heat with the mixed ortho-chlorotoluene raw material to be entered into the para-chlorine tower. The top gas outlet of the para-chlorine tower 1 is connected to the heating medium inlet of the second reboiler 4. The heating medium outlet of the second reboiler 4 is provided with two pipelines, one of which is connected to the top reflux port of the para-chlorine tower and the other is connected to the ortho-chlorine tower. 1, the 4th feed opening of chlorine tower is connected, the gaseous phase material that the chlorine tower top is discharged enters among the second reboiler 4 and the adjacent chlorine tower still material indirect heat exchange as heat source, gaseous phase material changes liquid phase material into, a liquid phase material part enters the adjacent chlorine tower middle part, and all the other liquid phase materials return to the chlorine tower top; Described adjacent chlorine tower is provided with the 3rd feed opening for mixing adjacent / para-chlorotoluene raw material feeding, the 4th feed opening for feeding the chlorine tower top material, adjacent chlorine tower 2 top gas outlet is connected with the first condenser 6, the second condenser 7 successively, the outlet of the second condenser 7 is provided with two pipelines, wherein one pipeline is connected with the overhead reflux port of adjacent chlorine tower, and another pipeline is used to extract the ortho-chlorotoluene product; The feed line of adjacent chlorine tower 2 is connected with the 3rd feed opening through the first condenser 6, and mixing adjacent / para-chlorotoluene raw material enters adjacent chlorine tower 2 after the gaseous phase material heat exchange that is discharged with the adjacent chlorine tower top in condenser; Described adjacent chlorine tower 2 tower still discharge port is connected with the second feed opening of chlorine tower 1.

[0046] The chlorine tower 1 adopts a multi-tube tower. The chlorine tower has a total of 1392 inner tubes. The cross section of each inner tube is circular and the cross-sectional area is 7cm. 2 Each inner tube is filled with triangular spiral packing (diameter 3mm, specific surface area 2800m 2 / m 3 , porosity 93%, theoretical plate number of packing is 55 pieces / m), and the total packing height is 2.68m; the gas-liquid phase flow rate in each inner tube remains uniform, the amount of packing filled in each inner tube remains consistent, and the reflux liquid spray density at the top of each inner tube remains consistent.

[0047] The adjacent chlorine tower 2 adopts a multi-tube tower. There are 2325 inner tubes in the adjacent chlorine tower. The cross section of each inner tube is circular and the cross-sectional area is 7cm. 2 Each inner tube is filled with triangular spiral packing (diameter 3mm, specific surface area 2800m 2 / m 3, porosity 93%, theoretical plate number of packing is 55 pieces / m), the total packing height is 2.42m; the gas-liquid phase flow rate in each inner tube remains uniform, the amount of packing filled in each inner tube remains consistent, and the reflux liquid spray density at the top of each inner tube remains consistent.

[0048] In the para-chlorine tower 1, the first feed inlet is 30 theoretical plate heights higher than the second feed inlet.

[0049] In the ortho-chlorine tower 2, the fourth feed inlet is 25 theoretical plate heights higher than the third feed inlet.

[0050] The object of distillation separation is a mixed o-chlorotoluene / p-chlorotoluene raw material at room temperature, in which the mass fraction of o-chlorotoluene is 50.00 wt %, and the mass fraction of p-chlorotoluene is 50.00 wt %.

[0051] The mixed o- / p-chlorotoluene raw material is distilled and separated based on the energy-saving system integrating the multi-effect distillation and the low pressure drop distillation tower, and the method is as follows:

[0052] Para-chlorotoluene tower 1 and ortho-chlorotoluene tower 3 are fed simultaneously, and the feed mass flow rate of mixed ortho-chlorotoluene raw material into para-chlorotoluene tower 1 and ortho-chlorotoluene tower 3 is 500 kg / h;

[0053] The mixed o-chlorotoluene / p-chlorotoluene raw material enters the heat exchanger 5, exchanges heat with the p-chlorotoluene product extracted from the p-chlorotoluene tower 1, and the raw material is preheated to 99.7°C. Then, it enters the p-chlorotoluene tower 1 from the first feed port. The top pressure of the p-chlorotoluene tower 1 is controlled to be 20kPa (absolute pressure), the top temperature is 104.7°C, the bottom pressure is 23.5kPa (absolute pressure), and the bottom temperature is 112.6°C. The gaseous material discharged from the top of the p-chlorotoluene tower 1 (o-chlorotoluene content is 58.20wt%, and the rest is p-chlorotoluene) enters the second reboiler 5 As a heat source, an indirect heat exchange is performed with the material in the tower reactor of the adjacent chlorine tower 2, and the liquid phase material is transformed into the liquid phase material through phase change. The liquid phase material is divided into two strands of material, and the material accounting for 9.69wt% of the total liquid phase material enters the middle part of the adjacent chlorine tower 2 from the fourth feed opening, and the remaining material returns to the para-chlorine tower 1 from the top of the tower; a para-chlorotoluene product (mass flow rate of about 500kg / h, the mass fraction of para-chlorotoluene is 99.5wt%) is extracted from the tower reactor of the para-chlorine tower 1, and the para-chlorotoluene product is heat exchanged with the mixed o- / para-chlorotoluene raw material to be entered into the para-chlorine tower 1 in a heat exchanger 5;

[0054] Mixed adjacent / parachlorotoluene raw material enters in the first condenser 6, with the gaseous phase material heat exchange of adjacent chlorotower 2 tower tops being discharged, be preheated to 50 ℃, enter adjacent chlorotower 2 from the 3rd opening for feed again, the tower top pressure of controlling adjacent chlorotower 2 is 5kPa (absolute pressure), and tower top temperature is 69.2 ℃, and tower top reflux ratio is 14.8, and tower reactor pressure is 7.2kPa, and tower reactor temperature is 80.6 ℃; Adjacent chlorotower tower reactor material (the content of ortho-chlorotoluene is 25.9wt%, and all the other are parachlorotoluene) is discharged from the second opening for feed Enter the para-chlorine tower; the gaseous material discharged from the top of the ortho-chlorine tower 2 enters the first condenser 6, and is heat exchanged with the mixed ortho-chlorine / para-chlorotoluene raw material to be entered into the ortho-chlorine tower 2. Since the gaseous material is more than the raw material feed flow rate, it enters the second condenser 7 and is further cooled to 40°C by circulating water and converted into a liquid material. Part of the liquid material is returned to the ortho-chlorine tower 2 from the top of the tower, and the remaining liquid material is extracted as an ortho-chlorotoluene product (mass flow rate of 500kg / h, a mass fraction of ortho-chlorotoluene of 99.5wt%).

[0055] The main energy consumption of the present embodiment is the heat load of the chlorine tower reactor, which is about 726.1kW. Compared with Comparative Example 1, energy consumption has been saved by 46.5%. The tower reactor material of the chlorine tower is composed of 99.5wt% parachlorotoluene, and the tower top is composed of orthochlorotoluene content is 58.20wt%, parachlorotoluene content 41.80wt%. During single tower operation, the tower top is composed of 99.5wt% orthochlorotoluene, and the tower reactor is composed of 99.5wt% parachlorotoluene. Compared with single tower operation, the difference between the tower reactor material composition and the tower top material composition of the present embodiment is relatively smaller; adjacent chlorine tower is also like this. That is to say, the tower top gas phase temperature is higher than the adjacent chlorine tower reactor temperature, and higher tower top temperature can strengthen the temperature difference with the adjacent chlorine tower reactor bubble point evaporation temperature, which is favourable for series distillation operation.

[0056] Comparative Example 1

[0057] A single-tower process was used to separate mixed o- and p-chlorotoluene. The mixed o- and p-chlorotoluene feedstock was the same as in Example 1. A 50-meter-tall conventional distillation tower was used. Because the small particle packing used in Example 1 could not be used with a single tower, a commonly used industrially used ceramic corrugated packing with 5 theoretical plates per meter was used in the single tower.

[0058] The distillation tower adopts middle feeding, the feed mass flow rate of the raw material is 1000kg / h, o-chlorotoluene is produced from the top of the tower, and p-chlorotoluene is produced from the bottom of the tower.

[0059] In embodiment 1, only have chlorine tower 1 adopted additional fresh steam as the rectification heat source, in order to have comparability, when single tower rectifying operation, adopted and the operating parameter similar to chlorine tower, namely rectifying tower overhead pressure is 20kPa (absolute pressure), under this condition, in order to guarantee that the massfraction of the ortho-chlorotoluene of tower top extraction is 99.5wt%, the massfraction of the para-chlorotoluene of tower reactor extraction is 99.5wt%, needing to maintain the ceramic corrugated packing height is 29 meters, tower top reflux ratio is 45, when operating with this understanding, pressure drop in the tower was about 10kPa.In the single tower rectifying operation, tower top temperature is 104.6 ℃, and tower reactor pressure is 30kPa (absolute pressure), and tower reactor temperature is 120 ℃.

[0060] The parachlorotoluene extracted from the bottom of the tower is exchanged with the mixed o- / p-chlorotoluene feedstock, preheating the feedstock from room temperature to 70.2°C. In this state, the heat load of the bottom of the tower is 1358.2kW.

Claims

1. An energy-saving system integrating a multi-effect distillation column and a low-pressure-drop distillation column, characterized in that: The invention comprises a para-chlorine tower (1) and an ortho-chlorine tower (2), wherein the para-chlorine tower (1) is provided with a first reboiler (3), and the ortho-chlorine tower (2) is provided with a second reboiler (4); a first feed port for feeding a mixed ortho-chlorotoluene raw material and a second feed port for feeding a tower kettle material of the ortho-chlorine tower are provided in the middle of the para-chlorine tower (1); a discharge pipeline is provided in the tower kettle of the para-chlorine tower (1) for extracting a para-chlorotoluene product; the discharge pipeline is provided with a heat exchanger (5); the feed pipeline is connected to the first feed port through the heat exchanger (5) so that the mixed ortho-chlorotoluene raw material to be fed into the para-chlorine tower is heat-exchanged with the tower kettle material of the para-chlorine tower; the top gas outlet of the para-chlorine tower (1) is connected to the tower top reflux port of the para-chlorine tower and the first reboiler (4) of the ortho-chlorine tower (2) respectively. The ortho-chlorotoluene tower (2) is connected to four feed ports; the ortho-chlorotoluene tower is provided with a third feed port for feeding mixed ortho-chlorotoluene raw materials and a fourth feed port for feeding para-chlorotoluene tower top materials; the top gas outlet of the ortho-chlorotoluene tower (2) is connected to the first condenser (6) and the second condenser (7) in sequence; the outlet of the second condenser (7) is provided with two pipelines, one pipeline is connected to the tower top reflux port of the ortho-chlorotoluene tower, and the other pipeline is used to extract the ortho-chlorotoluene product; the feed pipeline of the ortho-chlorotoluene tower (2) is connected to the third feed port through the first condenser (6); the mixed ortho-chlorotoluene raw materials are heat-exchanged with the gaseous materials discharged from the tower top of the ortho-chlorotoluene tower in the first condenser and then enter the ortho-chlorotoluene tower (2); the tower bottom discharge port of the ortho-chlorotoluene tower (2) is connected to the second feed port of the para-chlorotoluene tower (1).

2. The energy-saving system integrating multiple-effect distillation and low-pressure-drop distillation tower according to claim 1, characterized in that: The para-chlorine tower is a multi-channel distillation tower with multiple parallel channels inside, and each channel is filled with high-efficiency fillers; the ortho-chlorine tower is a multi-channel distillation tower with multiple parallel channels inside, and each channel is filled with high-efficiency fillers.

3. The energy-saving system integrating multiple-effect distillation and low-pressure-drop distillation tower according to claim 2, characterized in that: The theoretical plate number of the high-efficiency filler is 50 to 80 pieces / m; in the para-chlorine tower, the filler height is 1.5 to 3 meters; in the ortho-chlorine tower, the filler height is 1.5 to 3 meters.

4. The energy-saving system integrating multiple-effect distillation and low-pressure-drop distillation tower according to claim 2 or 3, characterized in that: The high-efficiency filler is a triangular spiral filler, a θ ring wire mesh filler or a spiral spring wire filler.

5. The energy-saving system integrating multiple-effect distillation and low-pressure-drop distillation tower according to claim 1 or 2, characterized in that: In the para-chlorine tower, the first feed port is higher than the second feed port; in the ortho-chlorine tower, the fourth feed port is higher than or equal to the third feed port.

6. The energy-saving system integrating multiple-effect distillation and low-pressure-drop distillation tower according to claim 5, characterized in that: In the para-chlorine tower, the first feed port is 25 to 30 theoretical plate heights higher than the second feed port; in the ortho-chlorine tower, when the fourth feed port is higher than the third feed port, the fourth feed port is 25 to 30 theoretical plate heights higher than the third feed port.

7. A method for separating para-chlorotoluene and o-chlorotoluene based on the energy-saving system integrating the multiple-effect distillation and low-pressure-drop distillation tower according to claim 1, characterized in that: include: Feed the para-chlorine tower and the ortho-chlorine tower simultaneously; The mixed o- / p-chlorotoluene feedstock enters a heat exchanger and is heated by the p-chlorotoluene product extracted from the p-chlorotoluene tower, and then enters the p-chlorotoluene tower; the gaseous material discharged from the top of the p-chlorotoluene tower enters a second reboiler as a heat source, and indirectly exchanges heat with the o-chlorotoluene tower kettle material, and is converted into a liquid-phase material through a phase change. Part of the liquid-phase material enters the middle of the o-chlorotoluene tower, and the remaining material returns to the p-chlorotoluene tower from the top of the tower; the p-chlorotoluene tower kettle material exchanges heat with the mixed o- / p-chlorotoluene feedstock to be entered into the p-chlorotoluene tower in a heat exchanger and is extracted as the p-chlorotoluene product; The mixed o- / p-chlorotoluene raw material enters the first condenser, exchanges heat with the gaseous material discharged from the top of the o-chloro tower, and then enters the o-chloro tower; the o-chloro tower kettle material enters the p-chloro tower; the gaseous material discharged from the top of the o-chloro tower enters the first condenser, exchanges heat with the mixed o- / p-chlorotoluene raw material to be entered into the o-chloro tower, and then enters the second condenser to be cooled into liquid material. Part of the liquid material returns to the o-chloro tower from the top of the tower, and the remaining liquid material is used as the o-chlorotoluene product.

8. The method for separating parachlorotoluene and o-chlorotoluene according to claim 7, wherein: In the mixed o-chlorotoluene / p-chlorotoluene raw material, the mass fraction of o-chlorotoluene is 45-55 wt%, and the rest is p-chlorotoluene; The gaseous material discharged from the top of the para-chlorotoluene tower has an o-chlorotoluene content of 55 to 75 wt%, and the rest is para-chlorotoluene; The gaseous material discharged from the top of the para-chlorine tower enters the second reboiler as a heat source, exchanges heat with the material in the kettle of the ortho-chlorine tower, and is converted into liquid material through phase change. The material accounting for 8 to 13 wt% of the total liquid material enters the middle of the ortho-chlorine tower, and the rest of the material returns to the top of the para-chlorine tower; In the o-chlorotoluene reactor material, the content of o-chlorotoluene is 25-45 wt%, and the rest is p-chlorotoluene; The mass fraction of p-chlorotoluene in the p-chlorotoluene product is greater than 99.5wt%; the mass fraction of o-chlorotoluene in the o-chlorotoluene product is greater than 99.5wt%.

9. The method for separating parachlorotoluene and o-chlorotoluene according to claim 7, wherein: The mass flow ratio of the mixed o- / p-chlorotoluene feedstock entering the o-chloro tower to the mixed o- / p-chlorotoluene feedstock entering the p-chloro tower is 1:1 to 1:1.5; The mixed o-chlorotoluene / p-chlorotoluene raw material enters the heat exchanger and is preheated to 80-110° C. by the p-chlorotoluene product extracted from the p-chlorotoluene tower; The mixed o- / p-chlorotoluene raw material enters the first condenser and is preheated to 45-55° C. by the gaseous material discharged from the top of the o-chlorotoluene tower.

10. The method for separating para-chlorotoluene and o-chlorotoluene according to claim 7, wherein: The absolute pressure at the top of the parachlorine tower is 20-30 kPa, the temperature at the top is 104-110°C, the absolute pressure at the bottom of the tower is 21-35 kPa, the temperature at the bottom of the tower is 112-118°C, and the pressure drop of the parachlorine tower is 0.5-5 kPa; The top absolute pressure of the ortho-chlorine tower is 5-10 kPa, the top temperature is 65-75°C, the bottom pressure is 6.5-13 kPa, the bottom temperature is 80-100°C, the pressure drop of the ortho-chlorine tower is 0.5-5 kPa, and the reflux ratio is 12-15.

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