Caprolactam waste residue recovery system

Abstract

The utility model discloses a caprolactam waste residue recovery system in the technical field of caprolactam waste residue treatment, which comprises a raw material tank, a forward extraction tower, a reverse extraction tower, a rectifying tower and a benzene storage tank which are sequentially connected from front to back, the caprolactam is subjected to forward extraction and then reverse extraction separation, and a stripping tower is additionally arranged to effectively separate water vapor, so that the caprolactam waste residue recovery system can be used for recovering caprolactam. According to the treatment system, the caprolactam recovery rate of a rectification purification system can be increased, the waste residue discharge amount of a rectification system can be reduced, tower bottom residues of a rectification tower can be collected and removed through the film evaporator, and the problem that a discharging pipeline of the film evaporator is blocked can be effectively solved; the waste residue and waste water of the film evaporator can be purified and recycled again through a new process system, caprolactam in the waste residue can be recycled, the loss is reduced, the final waste water can be directly subjected to water treatment, and the cost of the treatment process is also reduced.

Description

Technical Field

[0001] This utility model relates to the field of caprolactam waste treatment technology, and in particular to a caprolactam waste recycling system. Background Technology

[0002] In the caprolactam polymerization process, extract water containing caprolactam is generated, with a caprolactam concentration of about 10%. This water needs to be evaporated and purified before being recycled to facilitate the recovery and reuse of caprolactam, thereby reducing loss and waste.

[0003] In the caprolactam recovery process, the extraction water from the polymerization stage needs to be collected and evaporated through an evaporation system to increase the concentration of the caprolactam aqueous solution to 85%. Then, the water and caprolactam are separated by heating with a heat transfer medium. Generally, water and other impurities are separated by a separation tower and a depolymerization tower, and the caprolactam is purified to obtain caprolactam with a purity of over 98%. Then, it is purified by multi-effect distillation to finally obtain qualified caprolactam, which can be used as a raw material for subsequent applications.

[0004] After purification in the distillation column, impurities will still be generated at the bottom of the column, mainly consisting of oligomers. These impurities, which contain a large amount of oligomers, are filtered through an evaporator film filter to obtain a large amount of waste residue. This waste residue also contains a large amount of caprolactam. Generally, the waste residue contains 58.5% caprolactam, 23.3% oligomers, and 18.2% NaOH, and requires subsequent waste residue treatment processes or has high recycling costs.

[0005] There is a need to effectively treat the waste residue to reduce losses, avoid subsequent environmental pollution, and lower the cost of waste residue treatment.

[0006] Based on this, this utility model designs a caprolactam waste recycling system to solve the above problems. Utility Model Content

[0007] The purpose of this invention is to provide a caprolactam waste residue recovery system. This system can improve the caprolactam recovery rate of the distillation purification system, reduce the waste residue discharge of the distillation system, and collect and remove the bottom residue of the distillation column through a thin-film evaporator, further optimizing the stable operation of the distillation system. It also reduces wastewater discharge and treats the waste residue in a timely manner, effectively solving the problem of blockage in the feed pipeline of the thin-film evaporator. This waste residue treatment system can re-purify and recover the waste residue and wastewater from the thin-film evaporator through a new process system, allowing the caprolactam in the waste residue to be reused. This not only reduces losses but also allows the final wastewater to be directly treated, thus reducing the cost of the treatment process.

[0008] This utility model is implemented as follows: a caprolactam waste residue recycling system, comprising:

[0009] Raw material tanks, forward extraction towers, reverse extraction towers, distillation towers, and benzene storage tanks;

[0010] The raw material tank is a closed storage tank, and the top of the raw material tank is connected to the slag discharge pipeline of the thin film evaporator;

[0011] The raw material tank, forward extraction column, reverse extraction column, distillation column and benzene storage tank are connected in sequence from front to back;

[0012] The raw material tank is also connected to the forward extraction tower by a raw material pump, a raw material cooler, and a raw material filter;

[0013] A supply pump is also installed at the rear end of the benzene storage tank, and the outlet of the supply pump is connected to the front end of the forward extraction tower through a pipeline.

[0014] A mixing pump and a mixing filter are also provided between the forward extraction tower and the reverse extraction tower, and the rear end of the mixing filter is connected separately to the feed inlet of the forward extraction tower and the reverse extraction tower, respectively.

[0015] The bottom drain outlets of both the forward extraction tower and the reverse extraction tower are connected to the impurity storage tank, and the drain outlet of the impurity storage tank is connected to the sewage treatment pipeline.

[0016] The rear outlet of the reverse extraction tower is connected to a stripping tower, and the top outlet of the reverse extraction tower is connected to a distillation tower; the drain outlet of the distillation tower is connected to an external sewage treatment pipeline.

[0017] The distillation column is provided with an outlet at the top and a spray pipe at the top. The outlet of the distillation column is connected to a reboiler. A reflux tank is provided between the reboiler and the spray pipe. The reflux tank is also connected to the feed inlet of the benzene storage tank.

[0018] The front end of the stripping tower is connected to the outlet of the reverse extraction tower, the rear end of the stripping tower is connected to the caprolactam recovery pipeline, and the top of the stripping tower is connected to an external exhaust pipe.

[0019] Furthermore, the raw material tank contains a crude caprolactam aqueous solution.

[0020] Furthermore, both the forward extraction tower and the reverse extraction tower are extraction towers.

[0021] Furthermore, a bottom storage tank is provided at the bottom of the distillation column. The bottom storage tank and the distillation column are an integral structure that are interconnected. A discharge pump is connected to the bottom of the bottom storage tank, and the bottom storage tank is connected to an external water treatment pipeline through the discharge pump.

[0022] Furthermore, a circulating heat exchanger is provided between the reverse extraction tower and the stripping tower. The circulating heat exchanger is a shell-and-tube heat exchanger, and both the reverse extraction tower and the stripping tower are connected to the tube side of the circulating heat exchanger.

[0023] The bottom of the stripping tower is connected to a discharge pump, the outlet of which is connected to the shell-side inlet of the circulating heat exchanger, and the shell-side outlet of the circulating heat exchanger is connected to the caprolactam recovery pipeline.

[0024] Furthermore, both the raw material tank and the front end of the reverse extraction tower are connected to demineralized water pipelines, and coolers are installed on the demineralized water pipelines of both the raw material tank and the reverse extraction tower.

[0025] The beneficial effects of this utility model are: 1. This utility model can promptly receive the slag discharge pipeline of the thin film evaporator in the previous process through the raw material tank, so as to avoid the blockage of waste residue and wastewater in the previous process and affect the mainstream process in the previous process, and make the extraction water recovery process in the previous process smoother.

[0026] 2. This device also includes a forward extraction tower and a reverse extraction tower, which can extract caprolactam from the waste residue into the benzene solution through the dissolution of benzene and caprolactam, while the oligomers are separated into the aqueous solution, and other impurities remain as solids. This effectively achieves the separation of caprolactam and oligomers. This device can directly extract caprolactam with higher purity, and then separate caprolactam from benzene through the reverse extraction tower, finally extracting caprolactam with higher purity, thus achieving the purpose of recycling caprolactam.

[0027] 3. This device also includes a benzene recovery system. Benzene is recovered again through a benzene storage tank and a distillation column, and then benzene is used again to extract caprolactam in a forward extraction column, forming a complete cycle. This system consumes almost no benzene solution and has no air involved throughout the process, avoiding the oxidation of caprolactam and resulting in higher extraction and recovery efficiency. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Figure 1 This is a schematic diagram of the overall recycling system of this utility model.

[0030] The attached diagram lists the components represented by each number as follows:

[0031] 1-Raw material tank, 11-Raw material pump, 12-Raw material cooler, 13-Raw material filter, 2-Forward extraction tower, 21-Mixed liquid pump, 22-Mixed filter, 23-Impurity storage tank, 3-Reverse extraction tower, 31-Stripping tower, 32-Unloading pump, 33-Circulating heat exchanger, 4-Distillation tower, 41-Bottom tank, 42-Reflux tank, 43-Reboiler, 44-Drain pump, 5-Benzene storage tank, 51-Supply pump, 6-Cooler. Detailed Implementation

[0032] Please see Figure 1 As shown, this utility model provides a caprolactam waste residue recycling system. To better understand the above technical solution, the following will describe the above technical solution in detail with reference to the accompanying drawings and specific embodiments.

[0033] In a specific embodiment of the technical solution of this utility model:

[0034] It includes a raw material tank 1, a forward extraction tower 2, a reverse extraction tower 3, a distillation tower 4, and a benzene storage tank 5;

[0035] Raw material tank 1 is a closed storage tank. Its top is connected to the slag discharge pipe of the thin-film evaporator. The inside of raw material tank 1 contains the waste residue discharged from the thin-film evaporator, mixed with water to form a crude caprolactam aqueous solution. Dissolving all substances in the waste residue facilitates subsequent purification and recovery of caprolactam. Both raw material tank 1 and the front end of the reverse extraction tower 3 are connected to demineralized water pipes. Coolers 6 are installed on the demineralized water pipes of both raw material tank 1 and the reverse extraction tower 3 to cool the demineralized water, reducing the vaporization of caprolactam and benzene, and decreasing the amount of caprolactam dissolved in water. This allows more caprolactam at low temperatures to dissolve in the benzene solution.

[0036] The raw material tank 1, forward extraction tower 2, reverse extraction tower 3, distillation tower 4, and benzene storage tank 5 are connected in sequence from front to back. Both forward extraction tower 2 and reverse extraction tower 3 are extraction towers. The function of forward extraction tower 2 is to dissolve caprolactam in liquid benzene, while reverse extraction tower 3 is to extract caprolactam dissolved in benzene, so that the caprolactam and benzene solution are finally separated into caprolactam liquid and benzene vapor, thereby achieving the purpose of separating and purifying caprolactam.

[0037] A raw material pump 11, a raw material cooler 12, and a raw material filter 13 are also connected between the raw material tank 1 and the forward extraction tower 2;

[0038] A supply pump 51 is also installed at the rear end of the benzene storage tank 5, and the outlet of the supply pump 51 is connected to the front end of the forward extraction tower 2 through a pipeline.

[0039] A mixing pump 21 and a mixing filter 22 are also installed between the forward extraction tower 2 and the reverse extraction tower 3. The rear end of the mixing filter 22 is connected to the feed inlet of the forward extraction tower 2 and the reverse extraction tower 3 respectively.

[0040] The bottom drain outlets of both the forward extraction tower 2 and the reverse extraction tower 3 are connected to the impurity storage tank 23. Generally, it is sufficient to set up the same impurity storage tank 23, and there is no need to set up a separate impurity storage tank 23. In the end, the wastewater needs to be discharged into the wastewater treatment pond, and the drain outlet of the impurity storage tank 23 is connected to the wastewater treatment pipeline.

[0041] The rear outlet of the reverse extraction tower 3 is connected to the stripping tower 31, and the top outlet of the reverse extraction tower 3 is connected to the distillation tower 4; the drain outlet of the distillation tower 4 is connected to an external sewage treatment pipeline.

[0042] A gas outlet is provided at the top of the distillation column 4, and a spray pipe is also provided at the top of the distillation column 4. The gas outlet of the distillation column 4 is connected to the reboiler 43. A reflux tank 42 is provided between the reboiler 43 and the spray pipe. The reflux tank 42 is also connected to the feed inlet of the benzene storage tank 5. A cooler 6 is also provided between the reflux tank 42 and the benzene storage tank 5 to cool and liquefy the benzene in vapor state, so as to facilitate subsequent recycling.

[0043] A bottom storage tank 41 is installed at the bottom of the distillation column 4. The bottom storage tank 41 and the distillation column 4 are interconnected as a whole. A discharge pump 44 is connected to the bottom of the bottom storage tank 41, and the bottom storage tank 41 is connected to an external water treatment pipeline through the discharge pump 44. The bottom storage tank 41 contains some mixed waste residue. This waste residue is small in quantity and consists of impurities removed from caprolactam. It only needs to be further treated in a wastewater treatment pond and does not require any additional processing.

[0044] The front end of stripping tower 31 is connected to the outlet of reverse extraction tower 3, the rear end of stripping tower 31 is connected to caprolactam recovery pipeline, and the top of stripping tower 31 is connected to an external exhaust pipe.

[0045] A circulating heat exchanger 33 is also provided between the reverse extraction tower 3 and the stripping tower 31. The circulating heat exchanger 33 is a shell and tube heat exchanger. Both the reverse extraction tower 3 and the stripping tower 31 are connected to the tube side of the circulating heat exchanger 33.

[0046] The bottom of the stripping tower 31 is connected to the unloading pump 32, the outlet of the unloading pump 32 is connected to the shell-side inlet of the circulating heat exchanger 33, and the shell-side outlet of the circulating heat exchanger 33 is connected to the caprolactam recovery pipeline.

[0047] This achieves the thermal recycling of caprolactam. Cold liquid caprolactam is heated by circulating heat exchanger 33 to obtain a caprolactam solution with better fluidity and higher temperature. A small amount of water vapor may also be mixed in. At this time, the water vapor is extracted by circulating heat exchanger 33, the caprolactam aqueous solution is heated, and the mixed water is separated by stripping tower 31. The high-temperature caprolactam is then heated by circulating heat exchanger 33 to heat the caprolactam sent from reverse extraction tower 3. The operation and use reduce heat loss, reduce costs, and are more energy-efficient.

[0048] It should be noted that:

[0049] 1. This system utilizes the incompatibility between benzene and water. At a specific temperature, generally below 40°C, caprolactam does not dissolve in water but only in benzene, thus separating caprolactam from water. The separation of benzene and caprolactam is even easier, as their evaporation temperatures are different, facilitating their separation. This separation can be effectively achieved through distillation column 4. 2. In distillation column 4 of this device, a reflux tank 42 is also used to spray the low-temperature liquefied benzene directly into the distillation column 4. Therefore, benzene does not need to be purified and can be reused repeatedly. Furthermore, the high-temperature vaporized benzene is liquefied by a condenser and then transported to the benzene storage tank 5 for storage. It is then fed to the forward extraction column 2 via a supply pump 51 for the separation of caprolactam.

[0050] In use, the waste residue from the thin-film evaporator is transported to the raw material tank 1 through a pipeline. The pipeline is used for transporting the waste residue, and the waste residue needs to be cooled by the cooler 6 to prevent various impurities from vaporizing or causing abnormalities.

[0051] The waste residue is then dissolved in water in the raw material tank 1. After it is fully dissolved, the mixture of demineralized water, waste residue and waste liquid is transported by the raw material pump 11. The mixture is cooled by the raw material cooler 12, and the temperature is controlled below 40°C to ensure that the particulate matter in the mixture below 40°C is effectively filtered, thereby avoiding the generation of more particulate matter during the subsequent benzene liquefaction. The undissolved particulate matter is filtered by the raw material filter 13, so that only liquid matter is produced in the subsequent benzene liquefaction process, avoiding the mixing of impurities in the benzene liquid.

[0052] The waste residue mixture is extracted by forward extraction tower 2, and liquid benzene is injected into forward extraction tower 2 through a supply pump. At this time, because the waste residue mixture has been cooled by raw material cooler 12, benzene is in a low-temperature liquid state, caprolactam will dissolve in benzene, while other impurities cannot dissolve in benzene, thus achieving the purpose of extracting caprolactam.

[0053] Liquid benzene separates above the impurity water. The solution of benzene and caprolactam is pumped into the mixing filter 22 by the mixing pump 21 to filter the impurities. Any water impurities that were accidentally pumped in are precipitated. The impurity water at the bottom is then sent back to the forward extraction tower 2, while the pure benzene and caprolactam solution is sent to the reverse extraction tower 3.

[0054] In the reverse extraction column 3, the benzene liquid is heated, and the benzene quickly vaporizes. The gaseous benzene is collected in the distillation column 4 and continuously heated in the reboiler 43 before being transferred to the reflux tank 42. The gaseous benzene then flows into the benzene storage tank 5 for storage and reuse. A cooler 6 is added between the reflux tank 42 and the benzene storage tank 5 to cool and liquefy the benzene for storage and reuse. The liquid benzene in the forward extraction column 2 is supplied from the benzene storage tank 5 via the supply pump 51, achieving the purpose of recycling. At the same time, other impurities may be mixed into the reflux tank 42. If there are still liquid impurities after heating in the reboiler 43, they are refluxed back into the distillation column 4. Finally, these liquid impurities are in small quantities and can be collected in the bottom storage tank 41 and then transported to the wastewater pond of the water treatment process by the discharge pump 44 for microbial treatment.

[0055] The caprolactam liquid separated by the reverse extraction tower 3 is sent to the stripping tower 31 to separate a small amount of mixed water vapor. After the water is removed, the high-purity caprolactam is transported to the normal production process via the unloading pump 32. This completes the caprolactam purification process.

[0056] This device recycles and reuses the waste residue and wastewater from thin-film evaporators that would otherwise be discarded or scrapped. These wastes originate from the purification residue of caprolactam extraction water. This system extracts and recycles these useless substances, eliminating the need for additional waste treatment processes. The entire system experiences minimal energy loss and does not consume other materials, thus achieving energy conservation and emission reduction.

[0057] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A recovery system of caprolactam waste residues, characterized by, The application relates to a crude caprolactam extraction device. The device comprises a raw material tank (1), a forward extraction tower (2), a reverse extraction tower (3), a rectifying tower (4) and a benzene storage tank (5). The raw material tank (1) is a closed storage tank, and the top of the raw material tank (1) is connected with a residue discharge pipeline of a thin film evaporator. The raw material tank (1), the forward extraction tower (2), the reverse extraction tower (3), the rectifying tower (4) and the benzene storage tank (5) are sequentially connected from front to back. A raw material pump (11), a raw material cooler (12) and a raw material filter (13) are further connected between the raw material tank (1) and the forward extraction tower (2). A supply pump (51) is further arranged at the rear end of the benzene storage tank (5), and the discharge outlet of the supply pump (51) is connected with the front end of the forward extraction tower (2) through a pipeline. A mixed liquid pump (21) and a mixed filter (22) are further arranged between the forward extraction tower (2) and the reverse extraction tower (3), and the rear end of the mixed filter (22) is individually connected with the feed inlets of the forward extraction tower (2) and the reverse extraction tower (3). The bottom discharge outlets of the forward extraction tower (2) and the reverse extraction tower (3) are connected with an impurity storage tank (23), and the drain outlet of the impurity storage tank (23) is connected with a sewage treatment pipeline. The rear end discharge outlet of the reverse extraction tower (3) is connected with a stripping tower (31), and the top gas outlet of the reverse extraction tower (3) is connected with the rectifying tower (4); and the drain outlet of the rectifying tower (4) is connected with an external sewage treatment pipeline. A gas outlet is arranged at the top of the rectifying tower (4), a spraying pipeline is further arranged at the top of the rectifying tower (4), a reboiler (43) is connected with the gas outlet of the rectifying tower (4), a reflux tank (42) is arranged between the reboiler (43) and the spraying pipeline, and the reflux tank (42) is further connected with the feed inlet of the benzene storage tank (5). The front end of the stripping tower (31) is connected with the discharge outlet of the reverse extraction tower (3), the rear end of the stripping tower (31) is connected with a caprolactam recovery pipeline, and the top of the stripping tower (31) is connected with an exhaust pipeline.

2. The caprolactam waste residue recovery system according to claim 1, characterized by: The inside of the raw material tank (1) is a crude caprolactam aqueous solution.

3. The caprolactam waste residue recovery system according to claim 1, characterized by: The forward extraction tower (2) and the reverse extraction tower (3) are both extraction towers.

4. The caprolactam waste recovery system according to claim 1, wherein: A tower bottom storage tank (41) is arranged at the bottom of the rectifying tower (4), the tower bottom storage tank (41) and the rectifying tower (4) are an integral structure in communication, a discharge pump (44) is connected with the bottom of the tower bottom storage tank (41), and the tower bottom storage tank (41) is connected with an external water treatment pipeline through the discharge pump (44).

5. The caprolactam waste recovery system according to claim 1, wherein: A circulating heat exchanger (33) is further arranged between the reverse extraction tower (3) and the stripping tower (31), the circulating heat exchanger (33) is a tube-shell heat exchanger, and the reverse extraction tower (3) and the stripping tower (31) are both connected with the tube side of the circulating heat exchanger (33). A discharge pump (32) is connected with the bottom of the stripping tower (31), the liquid outlet of the discharge pump (32) is connected with the shell side inlet of the circulating heat exchanger (33), and the shell side outlet of the circulating heat exchanger (33) is connected with a caprolactam recovery pipeline.

6. The caprolactam waste recovery system according to claim 1, wherein: The front end of the raw material tank (1) and the reverse extraction tower (3) are connected with desalted water pipeline, and the desalted water pipeline of the raw material tank (1) and the reverse extraction tower (3) are provided with coolers (6).

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