Cooling crystallization system of DMT

Abstract

The utility model discloses a DMT cooling crystallization system, which comprises an ester exchange reaction kettle, a DMT crystallization tank and a DMT slurry storage tank, an outlet is arranged at the bottom of the ester exchange reaction kettle, an outlet pipeline at the bottom of the ester exchange reaction kettle is connected to the DMT crystallization tank, a material circulation line is arranged on the side surface of the DMT crystallization tank, a vacuum treatment line is connected to the top of the DMT crystallization tank, and an outlet is arranged at the bottom of the DMT crystallization tank. The DMT crystallization device is reasonable in structural layout, a series of process steps such as output of mixed liquid containing DMT components, vacuum cooling crystallization and output and storage of suspended slurry can be completed in sequence, a material circulation line is designed to replace a stirring mechanism in an existing DMT crystallization tank, and the DMT crystallization device is simple in structure, convenient to operate and high in practicability. Key equipment of the system is optimized, and the system has the advantages of simplifying the equipment structure and reducing the equipment failure rate.

Description

Technical Field

[0001] This utility model relates to the technical field of material cooling crystallization precipitation equipment, and more specifically, to a cooling crystallization system for DMT. Background Technology

[0002] Globally, tens of millions of tons of waste textiles are generated annually, but only a small portion can be recycled. Seventy percent of these are disposed of using the most "primitive" methods such as landfill and incineration, placing a tremendous burden on the environment. The chemical recycling process for producing recycled DMT (dimethyl terephthalate) is a technology that uses waste textiles (primarily composed of polyester fibers, approximately 90% or more) as raw materials for resource recycling. This process involves a series of steps, including textile sorting, crushing, depolymerization, concentration, and transesterification. After the transesterification process, extractable DMT components are produced. Companies need to design a simple, low-failure-rate DMT cooling and crystallization system to meet production requirements, hence this project. Utility Model Content

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a cooling crystallization system for DMT. This invention has a reasonable structural layout and can sequentially complete a series of process steps such as outputting a mixture containing DMT components, vacuum cooling crystallization, and outputting and storing a suspension slurry. This invention designs a material circulation line to replace the stirring mechanism in the existing DMT crystallization tank, thereby optimizing the key equipment of the system and having the advantages of simplifying the equipment structure and reducing the equipment failure rate.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A cooling crystallization system for DMT includes an ester exchange reactor, a DMT crystallization tank, and a DMT slurry storage tank. The ester exchange reactor has an outlet at its bottom, and the outlet pipe at the bottom of the ester exchange reactor is connected to the DMT crystallization tank. A material circulation line is installed on the side of the DMT crystallization tank, and a vacuum processing line is connected to the top of the DMT crystallization tank. The DMT crystallization tank has an outlet at its bottom, and the outlet pipe at the bottom of the DMT crystallization tank is connected to the DMT slurry storage tank.

[0006] Furthermore, a first angle valve is installed at the bottom outlet of the transesterification reactor, and a first discharge pump is installed on the connecting pipeline between the transesterification reactor and the DMT crystallizer. The first angle valve and the inlet end pipeline of the first discharge pump are connected, and an venting pipeline is connected to the connecting pipeline between the first angle valve and the first discharge pump.

[0007] Furthermore, the material circulation line includes a circulation pump, a feed pipe, and a return pipe. One end of the feed pipe is connected to the inlet of the circulation pump, and the other end penetrates into the interior of the DMT crystallizer and extends close to the bottom outlet of the DMT crystallizer. One end of the return pipe is connected to the outlet of the circulation pump, and the other end passes through and connects to the middle section of the side wall of the DMT crystallizer.

[0008] Furthermore, the DMT crystallizer has a cylindrical sidewall, and the return pipeline is side-cut connected to the DMT crystallizer. The jet from the return pipeline forms a spiral falling path inside the DMT crystallizer.

[0009] Furthermore, a level gauge is installed on the side of the DMT crystallizer, the lower half of the DMT crystallizer is inverted cone shape, and the bottom outlet of the DMT crystallizer is located at the tip of the inverted cone.

[0010] Furthermore, a second angle valve is installed at the bottom outlet of the DMT crystallizer. The pipeline of the second angle valve is connected to the top of the DMT slurry storage tank. A first valve is installed on the pipeline connecting the second angle valve and the DMT slurry storage tank. A backflushing pipeline is connected to the pipeline connecting the second angle valve and the DMT slurry storage tank. The backflushing pipeline is connected close to the second angle valve and is equipped with a second valve.

[0011] Furthermore, the vacuum processing line includes a vacuum unit, the gas phase inlet pipe of which is connected to the top of the DMT crystallizer, a first condenser and a second condenser are connected in series on the connecting pipe between the vacuum unit and the DMT crystallizer, the gas phase outlet pipe of the vacuum unit is connected to a third condenser, and the liquid phase outlet pipe of the vacuum unit is connected to a first methanol collection tank, the first methanol collection tank being connected to a DMT slurry storage tank.

[0012] Furthermore, the vacuum processing line also includes a condensation reflux pipeline and a residual treatment pipeline. The liquid phase outlets of the first condenser and the second condenser are both connected to the condensation reflux pipeline. One end of the residual treatment pipeline is connected to the condensation reflux pipeline, and the other end is connected to a second methanol collection tank. The second methanol collection tank is connected to the DMT slurry storage tank.

[0013] The beneficial effects of this utility model are:

[0014] 1. The present invention has a reasonable structural layout. The present invention can sequentially complete a series of process steps such as outputting a mixture containing DMT components, vacuum cooling crystallization, and outputting and storing a suspension slurry. The present invention ultimately contains DMT crystals in the suspension slurry stored in the DMT slurry storage tank, which is ready for DMT centrifugal separation operation.

[0015] 2. The vacuum treatment pipeline design of this utility model has multiple methanol condensation and reuse structures, which allows the vaporized methanol to be recycled again. This not only treats the exhaust gas but also reduces the system production cost.

[0016] 3. This utility model replaces the stirring mechanism in the existing DMT crystallizer by designing a material circulation line. The material circulation line can side-cut and circulate the liquid material in the DMT crystallizer, so that the material moves fully and improves the crystallization efficiency of the DMT component in the material. Since there is no need for a stirring mechanism, the probability of equipment failure can also be reduced. This utility model extends the material collection pipe of the material circulation line close to the bottom outlet of the DMT crystallizer to solve the problem of bottom material deposition. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structural principle of a cooling crystallization system for DMT in this embodiment;

[0018] Figure 2 This is a schematic diagram of the side-feeding method of the DMT crystallizer and a schematic diagram of the material circulation line connection in this embodiment.

[0019] Figure reference numerals: 1. Ester exchange reactor; 11. First discharge pump; 12. First angle valve; 13. Drain line; 2. DMT crystallizer; 21. Material circulation line; 211. Circulation pump; 212. Feed line; 213. Return line; 22. Level gauge; 23. Second angle valve; 231. First valve; 24. Backflush line; 241. Second valve; 3. DMT slurry storage tank; 31. Second discharge pump; 4. Vacuum processing line; 41. Vacuum unit; 42. First condenser; 43. Second condenser; 44. Third condenser; 45. First methanol collection tank; 46. First reuse pump; 47. Condensation reflux line; 48. Residual treatment line; 49. Second methanol collection tank; 49. Second reuse pump; 491. Detailed Implementation

[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0021] like Figure 1 and Figure 2The illustrated DMT cooling and crystallization system includes an ester exchange reactor 1, a DMT crystallization tank 2, and a DMT slurry storage tank 3. The product from the depolymerization and concentration of waste textiles undergoes an ester exchange reaction in the ester exchange reactor 1, ultimately forming a liquid containing DMT (the main components are methanol and DMT, with DMT soluble in methanol). The ester exchange reactor 1 has an outlet at its bottom, connected to the DMT crystallization tank 2. The DMT-containing liquid material produced by the ester exchange needs to be transported to the DMT crystallization tank 2 for crystallization. A material circulation line 21 is installed on the side of the DMT crystallization tank 2, which circulates the liquid. The material circulation line 21 replaces the traditional stirring mechanism to promote material movement. A vacuum treatment line 4 is connected to the top of the DMT crystallization tank 2. The material needs to be gradually cooled in a vacuum environment. The DMT component in the material will gradually precipitate and form crystals. The crystals are mixed with methanol liquid to form a suspension slurry containing DMT crystals. The bottom of the DMT crystallization tank 2 is provided with an outlet. The outlet pipe at the bottom of the DMT crystallization tank 2 is connected to the DMT slurry storage tank 3. The suspension slurry containing DMT crystals formed in the DMT crystallization tank 2 is finally transported to the DMT slurry storage tank 3 for storage. The outlet end of the DMT slurry storage tank 3 is connected to an output pipe. A second discharge pump 31 is installed on this output pipe. The second discharge pump 31 can pump the material to a DMT centrifugal separator for solid-liquid separation to obtain DMT crystal products (the DMT centrifugal separator is not marked on the figure). The above system structure of this utility model can meet the needs of the first step of DMT extraction, namely, cooling and crystallization production.

[0022] like Figure 1As shown, a first angle valve 12 is installed at the bottom outlet of the transesterification reactor 1. An angle valve is short for angle shut-off valve. The first angle valve 12 is used to control the opening and closing of the bottom outlet of the transesterification reactor 1. A first discharge pump 11 is installed on the connecting pipeline between the transesterification reactor 1 and the DMT crystallizer 2. The first discharge pump 11 transports the liquid material containing DMT generated by transesterification to the DMT crystallizer 2 for crystallization. The inlet pipeline of the first angle valve 12 is connected to the inlet pipeline of the first discharge pump 11. A drain line 13 is connected to the connecting pipeline of the first angle valve 12 and the first discharge pump 11. Under normal operating conditions, the drain line 13 and the first angle valve 12 do not open at the same time. That is to say, when the first angle valve 12 is open, the drain line 13 is closed. When the first angle valve 12 is open, it is used to output the liquid material containing DMT. After the output is completed, the first angle valve 12 is closed. Valve 12 is closed, but a large amount of liquid residue will still remain in the connecting pipeline between the ester exchange reactor 1 and the DMT crystallizer 2. The liquid residue will cause pipe blockage. Therefore, a venting pipeline 13 is designed to solve the above problem. After the first angle valve 12 is closed, the venting pipeline 13 is opened for a period of time. During this period, the venting pipeline 13 provides nitrogen gas at a pressure of 6N (0.6MPa) to vent the residue in the pipeline and blow it into the DMT crystallizer 2. This design can reduce the probability of system failure. There is also an abnormal situation where the bottom outlet of the ester exchange reactor 1 is blocked. After this abnormality occurs, it is necessary to disconnect the connecting pipeline between the ester exchange reactor 1 and the DMT crystallizer 2, and then open the venting pipeline 13 and the first angle valve 12 at the same time. Use the nitrogen gas at a pressure of 6N (0.6MPa) from the venting pipeline 13 to clear the bottom outlet of the ester exchange reactor 1.

[0023] like Figure 1 and Figure 2As shown, the material circulation line 21 includes a circulation pump 211, a feed pipe 212, and a return pipe 213. One end of the feed pipe 212 is connected to the inlet of the circulation pump 211, and the other end penetrates into the DMT crystallizer 2 and extends close to the bottom outlet of the DMT crystallizer 2. One end of the return pipe 213 is connected to the outlet of the circulation pump 211, and the other end passes through and connects to the middle section of the side wall of the DMT crystallizer 2. The installation height of the return pipe 213 is higher than that of the feed pipe 212. The material circulation line 21 is used to replace the stirring mechanism in a conventional crystallizer. Conventional crystallizers use an internal stirring mechanism to agitate the material in order to achieve... While improving the crystallization effect, as DMT crystals continuously precipitate, uneven sedimentation occurs on the impeller and stirring shaft during agitation, ultimately leading to increased vibration of the stirring mechanism and affecting equipment lifespan. To ensure stable and safe equipment operation, this invention uses a material circulation line 21 to replace the stirring mechanism. After the circulation pump 211 is turned on, it continuously draws and circulates the liquid in the DMT crystallization tank 2. The liquid creates a movement effect during circulation, meeting the conditions for crystallization. This invention bends the inlet end of the feed pipe 212 downwards and... The feed line 212 is extended close to the bottom outlet of the DMT crystallizer 2 (with a distance of 40-50cm between the feed line and the outlet). DMT crystals tend to deposit at the bottom outlet of the DMT crystallizer 2 after precipitation, and excessive deposition can cause blockage. Extending the feed line 212 close to the bottom outlet allows the suction force generated by the material circulation line 21 to agitate and remove the deposits at the bottom outlet, ensuring material movement at the bottom outlet as well. This solves the problem of material deposition and blockage near the bottom, ensuring that the material can move freely. In a cyclical motion state, this invention features a level gauge 22 installed on the side of the DMT crystallizer 2. The level gauge 22 controls the liquid level in the DMT crystallizer 2 to be higher than the feed pipe 212 of the material circulation line 21. This prevents the material circulation line 21 from operating without liquid flow. The lower half of the DMT crystallizer 2 is designed in an inverted cone shape, with the bottom outlet located at the apex of the cone. This allows the solution inside the tank to naturally converge towards the bottom outlet. The DMT crystallizer 2 has a cylindrical sidewall, and the return pipe 213 is side-connected to the DMT crystallizer 2. Figure 2 As shown, the jet formed at the outlet end of the return pipe 213 cuts into the DMT crystallizer 2. When the jet flow rate is large, the jet will fall along the inner wall of the DMT crystallizer 2 in a spiral path (the inner wall of the inverted cone-shaped DMT crystallizer 2 also plays a role in promoting the formation of the spiral path). When the return liquid spirals downward, the liquid movement time and movement stroke are lengthened, which is beneficial to the cooling of the liquid and the precipitation of DMT crystals.

[0024] During the DMT cooling process, a vacuum environment needs to be applied to DMT crystallizer 2 to facilitate the precipitation of DMT crystals, such as Figure 1As shown, the DMT crystallizer 2 is connected to the vacuum processing line 4, which includes a vacuum unit 41. The vacuum unit 41 is a commercially available complete set of equipment, and its structure is not described in detail. The gas phase inlet pipe of the vacuum unit 41 is connected to the top of the DMT crystallizer 2. The vacuum unit 41 can maintain the vacuum level inside the DMT crystallizer 2. Too high or too low a vacuum level will have an adverse effect on the reaction. For example, a low vacuum level will reduce production efficiency, while a high vacuum level will result in too obvious a DMT crystallization effect, making it difficult to discharge the material in time, causing a large amount of DMT to precipitate and leading to production interruption. This utility model uses the vacuum unit 41 to reduce the vacuum level inside the DMT crystallizer 2, controlling the pressure at around 30 kPa. During the crystallization reaction, methanol will continuously vaporize in the DMT crystallizer 2. The phenomenon is that vaporized methanol is drawn out by the vacuum unit 41, forming methanol-containing tail gas. This invention connects the vacuum unit 41 and the DMT crystallizer 2 with a first condenser 42 and a second condenser 43 in series. The first condenser 42 and the second condenser 43 achieve the methanol tail gas treatment effect, condensing the methanol in the tail gas into liquid methanol. The vacuum treatment line 4 also includes a condensation return line 47. The liquid phase outlets of the first condenser 42 and the second condenser 43 are both connected to the condensation return line 47. The outlet of the condensation return line 47 is connected to the DMT crystallizer 2. In other words, the methanol condensate from the methanol tail gas treatment needs to be collected and returned to the DMT crystallizer 2, thus solving the problem of excessive methanol consumption in the DMT crystallizer 2. To ensure the fluidity of the liquid in DMT crystallizer 2, and to facilitate the cooling of the liquid in DMT crystallizer 2 due to the low temperature of the condensed methanol liquid, an automatic control valve is installed on the condensate return line 47 to control the reflux flow rate of methanol liquid as needed. Since the condensed methanol liquid does not need to be completely returned to DMT crystallizer 2, this invention also includes a surplus treatment line 48. One end of the surplus treatment line 48 is connected to the condensate return line 47, and the other end is connected to a second methanol collection tank 49. Excess methanol liquid is transported to the second methanol collection tank 49 for collection. A second reuse pump 491 is installed at the outlet of the second methanol collection tank 49. The pipeline of the second methanol collection tank 49 is connected to the DMT slurry storage tank 3, and the second reuse pump 491 pumps the second methanol... The methanol liquid in the methanol collection tank 49 is used in the DMT slurry storage tank 3 (the DMT slurry storage tank 3 needs to be replenished with methanol to ensure fluidity). In this invention, the vacuum unit 41 has a gas phase outlet, and the gas phase outlet pipeline of the vacuum unit 41 is connected to a third condenser 44. Although the methanol content of the tail gas after being treated by the first condenser 42 and the second condenser 43 is greatly reduced, some residue still remains. This residue can be condensed again by the third condenser 44. The vacuum unit 41 itself has a condensation function, so it also has a liquid phase outlet. The liquid phase outlet of the vacuum unit 41 also outputs methanol liquid. The liquid phase outlet pipeline of the vacuum unit 41 is connected to a first methanol collection tank 45, where this portion of methanol liquid is transported for collection.The first methanol collection tank 45 is connected to the DMT slurry storage tank 3 via pipeline. A first reuse pump 46 is installed at the outlet of the first methanol collection tank 45. The first reuse pump 46 pumps the methanol liquid to the DMT slurry storage tank 3 for use.

[0025] like Figure 1 As shown, a second angle valve 23 is installed at the bottom outlet of the DMT crystallizer 2. The second angle valve 23 controls the opening and closing of the bottom outlet of the DMT crystallizer 2. During crystallization, the second angle valve 23 is closed. The pipeline of the second angle valve 23 is connected to the top of the DMT slurry storage tank 3. A first valve 231 is installed on the connecting pipeline between the second angle valve 23 and the DMT slurry storage tank 3. Only when both the second angle valve 23 and the first valve 231 are opened can the liquid in the DMT crystallizer 2 be output to the DMT slurry storage tank 3. Since a large number of DMT crystals are present in the liquid after the crystallization operation, the bottom outlet of the DMT crystallizer 2 may become blocked during the output process. Therefore, this invention connects a backflushing pipeline 24 to the connecting pipeline between the second angle valve 23 and the DMT slurry storage tank 3. The backflushing pipeline 24 is connected close to the second angle valve 23 and is equipped with a second valve 241. The second valve 241 and the first valve 231 are not opened at the same time, that is... During normal output, the second valve 241 of the backflushing line 24 is closed, and the first valve 231 is open to deliver the crystallizing liquid. When the bottom outlet of the DMT crystallizer 2 becomes blocked, the first valve 231 is closed and the second valve 241 is opened. At this time, the second angle valve 23 remains open. The backflushing line 24 is supplied with 6N nitrogen gas to backflush the bottom outlet of the DMT crystallizer 2 to achieve a clearing effect. Each clearing lasts for 2-3 seconds. After clearing, the second valve 241 is closed first, and then the first valve 231 is opened to deliver the crystallizing liquid normally. After repeating this process multiple times, the DMT crystals in the DMT crystallizer 2 can be easily transferred and delivered to the DMT slurry storage tank 3. The backflushing line 24 can also clear the connecting pipeline from the DMT crystallizer 2 to the DMT slurry storage tank 3. First, the second angle valve 23 is closed, and then the second valve 241 and the first valve 231 are opened simultaneously. The backflushing gas can clear the pipeline residue and ensure that the residue is emptied into the DMT slurry storage tank 3.

[0026] Example:

[0027] Based on the system design requirements, our company has selected a cylindrical vessel with a volume of 100.9 cubic meters for the ester exchange reactor 1 and a cylindrical vessel with a volume of 80.6 cubic meters for the DMT crystallizer 2. The circulating pump 211 in the material circulation line 21 is a device with a rated flow rate of 1300 m3 / hr and a rated head of 10 m. The actual working flow rate is 1300 m3 / hr and the working head is 10 m, which can meet the requirement of forming a spiral jet path in the DMT crystallizer 2. The ester exchange output material of this utility model is at about 73 degrees Celsius, and the crystallization operation in the DMT crystallizer 2 lasts for about 90 minutes, cooling down to 40 degrees Celsius, thereby meeting the requirement of a large amount of DMT crystals being fully extracted.

[0028] The above description is merely a preferred embodiment of this utility model. The protection scope of this utility model is not limited to the above embodiments. All technical solutions falling within the scope of this utility model's concept are protected. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of this utility model should also be considered within the protection scope of this utility model.

Claims

1. A cooling crystallization system for DMT, characterized in that, The apparatus includes an ester exchange reactor (1), a DMT crystallizer (2), and a DMT slurry storage tank (3). The ester exchange reactor (1) has an outlet at its bottom, and the outlet pipe at the bottom of the ester exchange reactor (1) is connected to the DMT crystallizer (2). A material circulation line (21) is installed on the side of the DMT crystallizer (2), and a vacuum processing line (4) is connected to the top of the DMT crystallizer (2). The DMT crystallizer (2) has an outlet at its bottom, and the outlet pipe at the bottom of the DMT crystallizer (2) is connected to the DMT slurry storage tank (3).

2. The cooling crystallization system for DMT according to claim 1, characterized in that, The bottom outlet of the transesterification reactor (1) is equipped with a first angle valve (12), and a first discharge pump (11) is installed on the connecting pipeline between the transesterification reactor (1) and the DMT crystallizer (2). The inlet end pipeline of the first angle valve (12) and the first discharge pump (11) are connected, and an venting pipeline (13) is connected on the connecting pipeline between the first angle valve (12) and the first discharge pump (11).

3. The cooling crystallization system for DMT according to claim 1, characterized in that, The material circulation line (21) includes a circulation pump (211), a feed pipe (212), and a return pipe (213). One end of the feed pipe (212) is connected to the inlet of the circulation pump (211), and the other end penetrates into the interior of the DMT crystallizer (2) and extends close to the bottom outlet of the DMT crystallizer (2). One end of the return pipe (213) is connected to the outlet of the circulation pump (211), and the other end is connected to the middle section of the side wall of the DMT crystallizer (2).

4. The cooling crystallization system for DMT according to claim 3, characterized in that, The DMT crystallizer (2) has a cylindrical sidewall, and the return pipe (213) is side-cut connected to the DMT crystallizer (2). The jet from the return pipe (213) forms a spiral falling path inside the DMT crystallizer (2).

5. The cooling crystallization system for DMT according to claim 1, characterized in that, A level gauge (22) is installed on the side of the DMT crystallizer (2). The lower half of the DMT crystallizer (2) is inverted cone shape, and the bottom outlet of the DMT crystallizer (2) is located at the tip of the inverted cone.

6. The cooling crystallization system for DMT according to claim 1, characterized in that, A second angle valve (23) is installed at the bottom outlet of the DMT crystallizer (2). The pipeline of the second angle valve (23) is connected to the top of the DMT slurry storage tank (3). A first valve (231) is installed on the pipeline connecting the second angle valve (23) and the DMT slurry storage tank (3). A backflushing pipeline (24) is connected on the pipeline connecting the second angle valve (23) and the DMT slurry storage tank (3). The backflushing pipeline (24) is connected close to the second angle valve (23). A second valve (241) is installed on the backflushing pipeline (24).

7. The cooling crystallization system for DMT according to claim 1, characterized in that, The vacuum processing line (4) includes a vacuum unit (41), the gas phase inlet pipe of the vacuum unit (41) is connected to the top of the DMT crystallizer (2), a first condenser (42) and a second condenser (43) are connected in series on the connecting pipe between the vacuum unit (41) and the DMT crystallizer (2), a third condenser (44) is connected to the gas phase outlet pipe of the vacuum unit (41), and a first methanol collection tank (45) is connected to the liquid phase outlet pipe of the vacuum unit (41), and the first methanol collection tank (45) is connected to the DMT slurry storage tank (3).

8. The cooling crystallization system for DMT according to claim 7, characterized in that, The vacuum processing line (4) also includes a condensation reflux line (47) and a residual treatment line (48). The liquid phase outlets of the first condenser (42) and the second condenser (43) are both connected to the condensation reflux line (47). One end of the residual treatment line (48) is connected to the condensation reflux line (47), and the other end is connected to a second methanol collection tank (49). The second methanol collection tank (49) is connected to the DMT slurry storage tank (3).

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