CN111659141A - Falling film distillation system for separating dichloromethane and white oil - Google Patents

Abstract

The present invention relates to a falling film distillation system for dichloromethane and white oil separation, which comprises a distillation column and an evaporator, wherein the distillation column includes an upper column body and a lower column body; The upper tube plate and the lower tube plate, a plurality of evaporation tubes, and a steam supply assembly that form a closed evaporation chamber with the circumferential inner wall of the upper tower body, wherein the plurality of evaporation tubes are spaced apart from each other, and the upper ports of the plurality of evaporation tubes are It is communicated with the liquid inlet pipe, and the lower port is communicated with the cavity formed by the lower tower body; the distillation system also includes a gas-liquid separator which can be communicated with the gas outlet pipe. The invention adopts a falling film evaporator, the material residence time is short, the steam working pressure is small and the steam consumption is low, and the evaporated white oil concentrate has low temperature, light color and high purity, and the evaporated dichloromethane gas is separated after separation. After the subsequent condensation and water separation, the content of white oil in dichloromethane is within 20ppm.

Description

Falling Film Distillation System for Dichloromethane and White Oil Separation

technical field

The invention belongs to the field of distillation, and in particular relates to a falling film distillation system for the separation of methylene chloride and white oil.

Background technique

At present, in the field of oil refining, dichloromethane and white oil need to be recovered in the production process of wet-process lithium battery diaphragm. Among them, white oil is mostly used as a pore-forming agent, and the white oil is extracted with dichloromethane after film formation. A mixture of dichloromethane and white oil was formed, and the mixture contained 5% white oil and 95% dichloromethane. In this process, a large amount of white oil and dichloromethane are used, so the separation and treatment of the mixed liquid, so as to recover and recycle the dichloromethane and the white oil, is the key to reducing the production cost of the lithium battery separator.

Some domestic use distillation methods to separate and purify dichloromethane and white oil, the light phase at the top of the tower is the separated dichloromethane, and the bottom liquid is the separated white oil. The light components are partially oxidized, destroying the structure of the white oil, and the removal effect of polar substances such as trace moisture is not good. The content of dichloromethane in the white oil is too high. High gas temperature will increase the condensation load of the condenser, resulting in an increase in the amount of circulating water, excessive white oil temperature, and deepening of the white oil color. The content of medium white oil is as high as 400ppm, and the content of methylene chloride in finished white oil is also as high as 500ppm.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a brand-new falling film distillation system for the separation of dichloromethane and white oil.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions:

A falling film distillation system for separation of methylene chloride and white oil, comprising a distillation column and an evaporator, the distillation column extends along a vertical direction, and includes an upper column body and a lower column body, wherein a liquid inlet pipe is located on the upper At the top of the tower body, the liquid outlet pipe is located at the bottom of the lower tower body, and the air outlet pipe is located at the upper side of the lower tower body;

The evaporator is arranged in the upper tower body, and includes an upper tube sheet and a lower tube sheet, which are respectively arranged at the top and bottom of the upper tower body and form a closed evaporation chamber with the circumferential inner wall of the upper tower body, and the two ends are connected with the upper tube sheet and the lower tube. A plurality of evaporating tubes connected through the plate and extending along the height direction of the upper tower body, and a steam supply assembly for supplying steam to an evaporation cavity formed by the upper tower body, wherein the plurality of evaporating tubes are spaced apart from each other, and the plurality of evaporation tubes The upper port of the pipe is communicated with the liquid inlet pipe, and the lower port is communicated with the cavity formed by the lower tower body;

The distillation system also includes a gas-liquid separator that can communicate with the gas outlet pipe.

Preferably, the evaporator further comprises a shaping plate arranged in the upper tower body and used for positioning the evaporation tubes, and a fixed tie rod used for hoisting the lower tube plate, wherein there is at least one shaping plate, and each shaping plate is connected to the inner wall of the upper tower body. A channel for steam flow is formed between the two, the fixed pull rod is arranged in parallel with the evaporation tube, the upper end is fixed on the setting plate, and the lower end is fixed on the lower tube plate. The setting of the shaping plate and the fixed tie rod can not only realize the positioning of the evaporation tube in the evaporation chamber; but also the steam flow channel formed by the shaping plate can improve the fluidity of the steam in the steam chamber to ensure the evaporation effect.

According to a specific implementation and preferred aspect of the present invention, there are a plurality of shaping plates, each of which is arranged horizontally, and has a fitting side that can fit on the inner wall of the upper tower body, and has a side edge that is cut off from the inner wall of the upper tower body on the corresponding side. The broken sides of the channel are formed by opening, wherein a plurality of shaping plates are distributed up and down along the length direction of the evaporation tube, and the formed channels are relatively staggered. Here, through the staggered channels, not only can the contact between the steam and the evaporation tube be fully realized to realize the indirect heating of the mixed liquid, but also a stable steam flow direction can be formed, which is beneficial to the evaporation of the mixture.

Preferably, a plurality of channels are spaced up and down, and are distributed in relative dislocation from left to right, and there are two fixed tie rods, which respectively connect the shaping plate on the same side of the channel and the lower tube plate at the bottom in series.

Preferably, the mixture of dichloromethane and white oil flows downward from the upper part of the evaporation tube, the steam in the steam chamber flows in the same direction as the mixture, and the steam flows in the steam chamber and forms a negative pressure. It can not only optimize the evaporation of the mixed liquid, but also further improve the effect of gas-liquid separation under negative pressure.

According to yet another specific implementation and preferred aspect of the present invention, the gas-liquid separator is a hydrocyclone, and is located outside the lower tower body, wherein the inlet of the hydrocyclone is communicated with the gas outlet pipe.

According to yet another specific implementation and preferred aspect of the present invention, the falling film distillation system further includes a liquid separation chamber connected to the liquid inlet pipe and positioned above the upper tube plate, the liquid separation chamber comprising a liquid separation tray positioned above the upper tube plate, A coaming plate surrounding the perimeter of the liquid separator, and a connecting piece connecting the coaming plate to the upper tower body, wherein the upper end of the coaming plate is open, the lower end of the liquid inlet pipe extends into the liquid separator chamber, and the liquid separator tray The upper part is provided with a distribution hole which can distribute the mixed liquid evenly to the lower corresponding upper nozzle. Here, through the arrangement of the liquid separation chamber, it is convenient to realize the uniform flow of the mixed liquid to each evaporation tube.

Preferably, there are multiple distribution holes and are divided into multiple groups, each group of distribution holes corresponds to the circumferential distribution of the upper nozzle of an evaporation tube below, and the center of the circle formed by the center of each group of distribution holes is set at On the center line of the corresponding upper nozzle at the bottom, the diameter of the circle is larger than the diameter of the upper nozzle, and the mixed liquid flowing out from each group of flow holes is attached to the inner wall of the evaporation tube from the periphery of the corresponding upper nozzle below. flow down. Due to the corresponding arrangement of each group of flow holes and evaporation tubes, the liquid flowing out from the flow separation holes can flow down from the circumference of the upper nozzle and fit the inner wall of the evaporation tube, so as to improve the evaporation efficiency.

Further, a plurality of evaporation tubes are arranged in an annular array between the upper tube plate and the lower tube plate, and the multi-component flow holes are arranged in one-to-one correspondence with the plurality of evaporation tubes, and the upper parts of the adjacent two evaporation tubes are arranged at intervals. A shunt hole is provided between the two groups of flow holes corresponding to the nozzle. The layout of the evaporation tubes facilitates the positioning of the positions of each group of separation holes, so as to achieve the effect of even distribution.

Preferably, the lower end of the liquid inlet pipe is located above the liquid separator, and the lower end of the liquid inlet pipe is also provided with a spray head, wherein the outflow of the mixture of dichloromethane and white oil from the spray head is greater than the self-splitting hole outgoing traffic. In this way, a certain liquid level should be formed in the liquid distribution chamber to ensure that the liquid flows out from each distribution hole evenly.

In addition, the falling film distillation system also includes an upper baffle extending upward from the top of the upper tube sheet, a lower baffle extending downward from the bottom of the lower tube sheet, and extending upward from the bottom of the lower column body and connected to the lower baffle Aligned extension plates, wherein the upper partition divides the upper tower body into two or more mixed liquid feeding areas, the liquid separation chamber is correspondingly arranged in the mixed liquid feeding area, and the liquid inlet pipe and the liquid separation chamber are one by one. Correspondingly arranged, and each liquid separation chamber is correspondingly provided with a liquid inlet pipe; the lower baffle separates the upper part of the lower tower body into a gas phase area corresponding to the mixed liquid feeding area, and the lower baffle is aligned with the extension The plates are spaced apart, the gas phase zone extends down to the top of the extension plate, two or more gas phase zones are communicated and arranged from the space between the lower partition plate and the extension plate, and the gas outlet pipe is located in the gas phase zone and above the side of the extension plate; The plate divides the lower part of the lower tower body into liquid phase areas corresponding to the gas phase area, and each liquid phase area is correspondingly provided with a liquid outlet pipe. The purpose of this setting is to implement the distillation process in and out of the distillation column multiple times and enter different evaporation zones to ensure the distillation effect.

Due to the implementation of the above technical solutions, the present invention has the following advantages compared with the prior art:

The invention adopts a falling film evaporator, the material residence time is short, the steam working pressure is small, and the steam consumption is low, and at the same time, the evaporated white oil concentrate has low temperature, light color and high purity, and the evaporated dichloromethane gas is separated after separation. After water separation with subsequent condensation, the content of white oil in dichloromethane is within 20 ppm, and in addition, the structure is simple and the implementation is convenient.

Description of drawings

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

Fig. 1 is the structural representation of the distillation system of the present invention;

Fig. 2 is the partial structure schematic diagram (distillation tower and evaporator) in Fig. 1;

Fig. 3 is the structural enlarged schematic diagram of the evaporator in Fig. 2;

Fig. 4 is the structural enlargement schematic diagram of distillation column upper part among Fig. 2;

Fig. 5 is the top view schematic diagram of the right liquid separation chamber in Fig. 4;

Among them: 1, distillation tower; 10, upper tower body; 11, lower tower body; 1a, liquid inlet pipe; 1b, liquid outlet pipe; 1c, gas outlet pipe;

2. Evaporator; 20. Upper tube sheet; 21. Lower tube sheet; 22. Evaporation tube; 23. Steam supply assembly; 230. Steam inlet; 231. Steam condensate outlet; 24. Forming plate (baffle plate); 24a, fit the side edge; 24b, disconnect the side edge; t, channel; 25, fix the pull rod;

3. Gas-liquid separator;

4. Separation chamber; 40. Separation plate; 40a, shunt hole; k, shunt hole group; 41, enclosure plate; 42, connecting piece;

5. Upper baffle; 6. Lower baffle; 7. Extension plate; h1, h2, mixed liquid feeding area; q1, q2, gas phase area; y1, y2, liquid phase area; 8, shower head.

Detailed ways

In order to make the above objects, features and advantages of the present application more clearly understood, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", " Back, Left, Right, Vertical, Horizontal, Top, Bottom, Inner, Outer, Clockwise, Counterclockwise, Axial , "radial", "circumferential" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the application and simplifying the description, rather than indicating or implying the indicated device or Elements must have a particular orientation, be constructed and operate in a particular orientation and are therefore not to be construed as limitations on this application.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In the description of the present application, "plurality" means at least two, such as two, three, etc., unless expressly and specifically defined otherwise.

In this application, unless otherwise expressly specified and limited, the terms "installed", "connected", "connected", "fixed" and other terms should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection , or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between the two elements, unless otherwise specified limit. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

In this application, unless otherwise expressly stated and defined, a first feature "on" or "under" a second feature may be in direct contact with the first and second features, or the first and second features indirectly through an intermediary touch. Also, the first feature being "above", "over" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is level higher than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower level than the second feature. It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or an intervening element may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for the purpose of illustration only and do not represent the only embodiment.

Referring to FIG. 1 , according to the present embodiment, a falling film distillation system for separating methylene chloride and white oil includes a distillation column 1 , an evaporator 2 , and a gas-liquid separator 3 .

Specifically, the distillation column 1 extends along the vertical direction, and includes an upper column body 10 and a lower column body 11, wherein the liquid inlet pipe 1a is located at the top of the upper column body 10, and the liquid outlet pipe 1b is located at the bottom of the lower column body 11, The air outlet pipe 1c is located at the upper side of the lower tower body 11 .

In this example, the distillation column 1 has a columnar shape and a circular cross section.

As shown in FIG. 2 , the evaporator 2 is arranged in the upper tower body 10 and includes an upper tube plate 20 and a lower tube which are respectively arranged at the top and bottom of the upper tower body 10 and form a closed evaporation cavity with the circumferential inner wall of the upper tower body 10 The plate 21, the plurality of evaporating tubes 22 extending through the upper tube plate 20 and the lower tube plate 21 at both ends and extending along the height direction of the upper tower body 10, and a steam supply assembly 23 for supplying steam to the evaporation chamber formed by the upper tower body , a setting plate 24 arranged in the upper tower body 10 and used for positioning the evaporation tube 22 , and a fixed tie rod 25 used for hoisting the lower tube plate 21 .

The plurality of evaporation tubes 22 are spaced apart from each other, and the upper ports of the plurality of evaporation tubes 22 are communicated with the liquid inlet pipe 1a, and the lower ports are communicated with the cavity formed by the lower tower body 11 .

Specifically, a plurality of evaporating tubes 22 are arranged in an annular array between the upper tube sheet 20 and the lower tube sheet 21 at intervals.

The steam supply assembly 23, which is a conventional component, includes a steam inlet 230 and a steam condensate outlet 231, and a steam generator, a steam pipe for connecting the steam generator with the steam inlet.

As shown in FIG. 3 , there are multiple shaping plates 24 (also called baffles), and a channel t for steam flow is formed between each shaping plate 24 and the inner wall of the upper tower body 10 , and the tie rod 25 and the evaporation tube 22 are fixed. They are arranged in parallel, and the upper end is fixed on the shaping plate 24 and the lower end is fixed on the lower tube plate 21 . The setting of the shaping plate and the fixed tie rod can not only realize the positioning of the evaporation tube in the evaporation chamber; but also the steam flow channel formed by the shaping plate can improve the fluidity of the steam in the steam chamber (form a baffle) to ensure the evaporation effect.

In this example, each of the setting plates 24 is arranged horizontally, and has a fitting side 24a that can fit on the inner wall of the upper tower 10, and a disconnected side that is disconnected from the inner wall of the upper tower 10 on the corresponding side to form a channel t 24b, wherein the plurality of shaping plates 24 are spaced up and down along the length direction of the evaporation tube 22, and the plurality of channels t formed are relatively staggered. Here, through the staggered channels, not only can the contact between the steam and the evaporation tube be fully realized to realize the indirect heating of the mixed liquid, but also a stable steam flow direction can be formed, which is beneficial to the evaporation of the mixture.

In this example, a plurality of channels t are spaced up and down, and are relatively dislocated from left to right. There are two fixed tie rods 25, which respectively connect the shaping plate 24 on the same side of the channel t and the lower tube plate 21 at the bottom in series. In this way, the positioning and installation of the evaporation tube is more stable.

At the same time, the mixed liquid of dichloromethane and white oil flows downward from the upper part of the evaporation tube 22, and the flow direction of the steam in the steam chamber is the same as the flow direction of the mixed liquid. Optimized for evaporation of the mixture.

In this example, the difference in boiling point between dichloromethane and white oil (low boiling point of dichloromethane, 39.8 °C, high boiling point of white oil, above 350 °C), can be preheated before the mixed liquid is added to the distillation column, as long as it evaporates When the temperature of the mixed liquid in the tube is greater than or equal to 39.8 °C, the mixed liquid is separated from the dichloromethane in the gas phase and the white oil in the liquid phase. Therefore, the vapor temperature in the evaporation chamber and the stable temperature difference of the mixed liquid in the evaporation tube are small, so that the vapor The dosage is significantly reduced.

In this example, the gas-liquid separator 3 is a hydrocyclone, and is located outside the lower tower body 11, wherein the inlet of the hydrocyclone is communicated with the gas outlet pipe 1c.

As for the hydrocyclone, it is a conventional product in the field, which can be obtained by means of direct outsourcing, and mainly separates the white oil in the methylene chloride gas.

At the same time, the hydrocyclone separator generates a slight negative pressure of about 0.074Mpa, and the gaseous dichloromethane in the gas phase area is sucked into the hydrocyclone separator for gas-liquid separation.

As shown in FIG. 4 , the falling film distillation system also includes a liquid separation chamber 4 connected to the liquid inlet pipe 1a and located above the upper tube plate 20 , an upper partition plate 5 extending upward from the top of the upper tube plate 20 , and a lower pipe The bottom of the plate 21 extends downward, and the lower partition 6 extends upward from the bottom of the lower tower body 11 and is aligned with the lower partition 6 .

Specifically, the upper baffle 5, the lower baffle 6 and the extension plate 7 are all one piece, so that the upper baffle 5 divides the upper tower body 10 into two mixed liquid feeding areas h1 and h2; the lower baffle 6 Correspondingly, the upper part of the lower tower body 11 is divided into two gas phase zones q1 and q2 corresponding to the mixed liquid feeding zones h1 and h2 one-to-one; The corresponding two liquid phase regions y1, y2.

In this example, there are two liquid-separating chambers 4, which are respectively arranged in the two mixed liquid feeding areas h1 and h2. There is an inlet pipe 1a.

The liquid-separating chamber 4 includes a liquid-separating plate 40 located above the upper tube plate 20, a surrounding plate 41 surrounding the liquid-separating plate 40, and a connecting piece 42 connecting the surrounding plate 41 to the upper tower body 10, wherein the The upper end of 41 is open, the lower end of the liquid inlet pipe 1a protrudes into the liquid distribution chamber 4, and the liquid distribution plate 40 is provided with a distribution hole 40a that can distribute the mixed liquid evenly to the corresponding upper nozzle below.

As shown in FIG. 5 , there are multiple distribution holes 40a and are divided into multiple groups, each distribution hole group k corresponds to the circumferential distribution of the upper nozzle of the evaporation tube 22 below, and the center of each group of distribution holes is formed by The center of the circle is set on the center line of the corresponding upper nozzle below, and the diameter of the circle is larger than the diameter of the upper nozzle. In this way, the mixed liquid flowing out from each group of orifices flows from the corresponding upper pipe below. The periphery of the port is in contact with the inner wall of the evaporation tube 22 to flow downward, so as to improve the evaporation efficiency and ensure the evaporation effect.

In this example, the lower partition plate 6 is spaced apart from the aligned extension plates 7 , so that the gas phase region extends down to the top of the extension plate 7 , and the two gas phase regions q1 and q2 extend from the space between the lower partition plate 6 and the extension plate 7 . The openings are connected to each other. The advantage of this setting is that whether it is the gas or liquid flowing out through the left or right evaporating tube, the gas part will float in the gas phase areas q1 and q2, and will be guided by the gas outlet pipe 1c on one side. The gas can be sent into the hydrocyclone separator to further complete the separation of the white oil in the dichloromethane gas.

At the same time, the lower part of the lower tower body 11 is divided into liquid phase zones y1 and y2 corresponding to the gas phase zones q1 and q2 by the bottom extension plate 7, and each liquid phase zone y1 and y2 is correspondingly provided with a liquid outlet pipe 1b, Here, the applicant explains why the bottom is divided into two liquid phase regions y1, y2, the main reason is that the collection of white oil after separation from the evaporation tube 22 above can be achieved correspondingly. In this way, when the left liquid inlet pipe 1a enters the mixed liquid and evaporates, the mixed liquid is separated into dichloromethane in the gas phase and white oil in the liquid phase, wherein the dichloromethane in the gas phase is sent into the hydrocyclone from the gas outlet pipe The white oil contained in the gaseous dichloromethane is separated, and the white oil of the liquid phase after evaporation is discharged from the liquid outlet pipe 1b on the left side, and at this time, the discharged white oil can be from the liquid inlet on the right side of the top of the distillation tower 1. The port enters the evaporation tube 22 on the right side to realize the secondary distillation of the white oil. After the secondary distillation, the dichloromethane that separates the gas phase is sent into the hydrocyclone for gas-liquid separation, and the liquid phase white oil after the secondary distillation is separated. It is discharged from the liquid outlet pipe 1b on the right side, and then the white oil is cooled, and the separation of methylene chloride and white oil can be completed.

In this example, the lower end of each liquid inlet pipe 1a is located above the liquid separator 40, and a shower head 8 is also provided at the lower end of the liquid inlet pipe 1a, wherein the mixture of dichloromethane and white oil is sprayed from The flow rate out of the head 8 is greater than the flow rate out of the branch hole 40a. In this way, a certain liquid level should be formed in the liquid distribution chamber to ensure that the liquid flows out from each distribution hole evenly.

In addition, this embodiment adopts the above-mentioned distillation system, and after secondary distillation, the content of methylene chloride in the finished white oil: ≤0.008% (80ppm); the content of white oil in methylene chloride: ≤0.002% (20ppm); the finished product Water in white oil: ≤0.02%. However, the above-mentioned indicators in the existing equipment can generally only be achieved: the content of methylene chloride in the finished white oil: ≤ 0.05% (500ppm); the content of white oil in the methylene chloride: ≤ 0.04% (400ppm). Therefore, by adopting the distillation system of the present application, the separation effect of white oil and dichloromethane can be greatly improved, and the technical purpose of low content of dichloromethane in white oil and low content of white oil in dichloromethane can be ensured.

To sum up, the distillation system in this example adopts the most advanced micro-negative pressure falling film evaporation process in China, and its characteristics are:

1) The material residence time is short, the steam working pressure is small, and the steam consumption is low;

2) The temperature of methylene chloride gas is low (below 50 ℃), which will not cause corrosion to the equipment during long-term use, and the condensation load of the condenser is small, and the circulating water consumption is low, which can reduce the production cost;

3) After evaporation, the temperature of the white oil concentrate is low, the color is light, and the purity is high, and the amount of white clay added during decolorization is reduced, which reduces the production cost;

4) The evaporated dichloromethane gas is firstly captured by high-efficiency flashing and then condensed by the condenser. The dichloromethane liquid has high purity, and then water is separated. Therefore, the content of white oil in dichloromethane can be obtained as 20ppm within.

The present invention has been described in detail above, and its purpose is to enable those skilled in the art to understand the content of the present invention and implement it, and cannot limit the scope of protection of the present invention by this, and the present invention is not limited to the above-mentioned embodiments, All equivalent changes or modifications made according to the spirit of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. a falling-film distillation system for dichloromethane and white oil separation, it comprises distillation column and evaporator, it is characterized in that: The distillation column extends along the vertical direction and includes an upper column body and a lower column body, wherein the liquid inlet pipe is located at the top of the upper column body, the liquid outlet pipe is located at the bottom of the lower column body, and the gas outlet pipe is located at the top of the upper column body. The upper part of the side of the lower tower body; The evaporator is arranged in the upper column body, and includes an upper tube plate and a lower tube plate, which are respectively arranged at the top and bottom of the upper column body and form a closed evaporation cavity with the circumferential inner wall of the upper column body. a plurality of evaporating tubes whose parts are in communication with the upper tube sheet and the lower tube sheet and extend along the height direction of the upper tower body, and a steam supply assembly that provides steam to the evaporation chamber formed by the upper tower body , wherein a plurality of the evaporation tubes are spaced apart from each other, and the upper ports of the plurality of evaporation tubes are communicated with the liquid inlet tube, and the lower ports are communicated with the cavity formed by the lower tower body; The distillation system further includes a gas-liquid separator that can communicate with the gas outlet pipe. 2. The falling film distillation system for separation of methylene chloride and white oil according to claim 1, wherein the evaporator further comprises a A shaping plate and a fixed tie rod for hoisting the lower tube plate, wherein there is at least one shaping plate, and a channel for steam flow is formed between each shaping plate and the inner wall of the upper tower body, and the fixing plate is The draw rod is arranged in parallel with the evaporation tube, and the upper end is fixed on the shaping plate, and the lower end is fixed on the lower tube plate. 3. The falling-film distillation system for separating methylene chloride and white oil according to claim 2, characterized in that: there are multiple said shaping plates, and each said shaping plate is arranged horizontally, and has a The fitting side that is closed on the inner wall of the upper tower body, and the disconnected side that is disconnected from the inner wall of the upper tower body on the corresponding side to form the channel, wherein a plurality of the shaping plates are along the evaporating tube. The longitudinal direction is distributed at intervals up and down, and the plurality of channels formed are relatively staggered. 4. The falling film distillation system for separating methylene chloride and white oil according to claim 3, characterized in that: a plurality of said passages are spaced up and down, and the left and right are relatively dislocated, and there are two said fixed tie rods, And the shaping plate located on the same side of the channel and the lower tube plate at the bottom are fixed and connected in series respectively. 5. The falling film distillation system for separating dichloromethane and white oil according to claim 1, is characterized in that: the mixed liquid of dichloromethane and white oil flows downward from the upper part of the evaporation tube, and the steam The steam in the cavity flows in the same direction as the mixed liquid, and the steam flows in the steam cavity and forms a negative pressure. 6. The falling-film distillation system for separating methylene chloride and white oil according to claim 1, wherein the falling-film distillation system further comprises a connection with the liquid inlet pipe and is located in the upper pipe The liquid separation chamber above the plate, the liquid separation chamber includes a liquid separation tray located above the upper tube plate, a surrounding plate surrounding the liquid separation tray, and a connection between the surrounding plate and the upper tower The connecting piece connected to the body, wherein the upper end of the enclosure plate is open, the lower end of the liquid inlet pipe extends into the liquid distribution chamber, and the liquid distribution plate is provided with a device that can evenly distribute the mixed liquid to The lower part corresponds to the shunt hole of the upper nozzle. 7. The falling-film distillation system for separating methylene chloride and white oil according to claim 6, wherein the diverter holes are multiple and divided into groups, and each diverter hole group corresponds to one below. The circumferential distribution of the upper nozzles of the evaporation tube, and the center of the circle formed by the center of each group of the distribution holes is set on the center line of the corresponding upper nozzle below, wherein the diameter of the circle is greater than According to the pipe diameter of the upper nozzle, the mixed liquid flowing out from each group of the distribution holes flows downward from the periphery of the corresponding upper nozzle below and fits the inner wall of the evaporation tube respectively. 8. The falling-film distillation system for separating methylene chloride and white oil according to claim 7, characterized in that: a plurality of said evaporating tubes are arranged in an annular array and are sequentially spaced on the upper tube plate and the upper tube plate. Between the lower tube sheets, a plurality of groups of the shunt holes are arranged in a one-to-one correspondence with a plurality of the evaporation tubes, and one of the two groups of the shunt holes corresponding to the upper nozzles of the two adjacent evaporation tubes. One of the shunt holes is used in between. 9 . The falling-film distillation system for separating methylene chloride and white oil according to claim 6 , wherein the lower end of the liquid inlet pipe is located above the liquid separator, and the lower end of the liquid inlet pipe is located above the liquid separator. 10 . The lower end of the liquid pipe is also provided with a shower head, wherein the flow rate of the mixture of dichloromethane and white oil flowing out of the shower head is greater than the flow rate flowing out of the distribution hole. 10. The falling film distillation system for separating methylene chloride and white oil according to claim 6, wherein the falling film distillation system further comprises an upper tube extending upward from the top of the upper tube plate. A partition, a lower partition extending downward from the bottom of the lower tube sheet, and an extension plate extending upward from the bottom of the lower tower body and aligned with the lower partition, wherein the upper partition will The upper tower body is divided into two or more mixed liquid feeding areas, the liquid separation chamber is correspondingly arranged in the mixed liquid feeding area, and the liquid inlet pipe is one with the liquid separation chamber. A corresponding arrangement is provided, and each of the liquid separation chambers is provided with a corresponding liquid inlet pipe; the lower baffle partitions the upper part of the lower tower body into corresponding ones of the mixed liquid feeding areas. a gas phase zone, and the lower baffle is spaced apart from the aligned extension plates, the gas phase zone extends down to the top of the extension plate, and two or more gas phase zones extend from the lower baffle and the extension plate The partitions of the plates are connected and arranged, and the gas outlet pipe is located in the gas phase area and above the side of the extension plate; the extension plate divides the lower part of the lower tower body into a corresponding gas phase area Each of the liquid phase areas is provided with a liquid outlet pipe correspondingly.

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