A benzene bottoms recovery system and method

Abstract

The application discloses a benzene residue recovery system and method, and relates to the technical field of recycling. The system comprises a first benzene distillation tower, desalted water and wastewater flowing out of the first benzene distillation tower are diluted in a second benzene distillation tower, and then are flowed into a condensate stripping tower to recover benzene. The second benzene distillation tower is arranged to dilute the wastewater, and the wastewater output by the first distillation tower is diluted by injecting desalted water into the second benzene distillation tower. The dilution solution flowing out of the second benzene distillation tower is subjected to benzene recovery by the condensate stripping tower, and the residue in the second benzene distillation tower does not need to be directly output to a residual benzene tank and then treated by an external mechanism.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of recycling, in particular to a benzene residue recovery system and method. BACKGROUND

[0002] In the benzene extraction process, benzene-soluble impurities are removed, and benzene is used as an extractant for recycling. In order to improve the extraction effect, the extractant must be continuously purified during the recycling process. The benzene residue produced during the purification process mainly contains benzene, caprolactam, benzene-soluble organic impurities, etc. The benzene-soluble impurities produced in the benzene extraction process of the caprolactam device are accumulated at the bottom of the benzene distillation and are intermittently collected and sent to the benzene residue tank. This part of the benzene residue contains 40% benzene, and the monthly production is 78 tons. This part of the benzene residue is a chemical hazardous waste, which needs to be regularly handled by a third party at the expense of the company. Not only does it cause the loss of system benzene, but it also costs money to handle, which is a great waste. SUMMARY

[0003] In view of the deficiencies of the prior art, the purpose of the present application is to provide a benzene residue recovery system and method, which recovers the benzene residue by setting up a tower. Water can be added to the feed pipe of the tower to form benzene-water azeotrope in the tower, and the benzene in the benzene residue can be recovered.

[0004] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0005] In a first aspect, the embodiments of the present application provide a benzene residue recovery system, which comprises a first benzene distillation tower, desalted water and waste water flowing out of the first benzene distillation tower flow through a second benzene distillation tower after being diluted, and then flow into a condensate stripping tower to recover benzene.

[0006] As a further implementation manner, the outlet of the first benzene distillation tower is connected with a first pump.

[0007] As a further implementation manner, the first pump is connected with the inlet of a second distillation tower.

[0008] As a further implementation manner, the outlet of the second distillation tower is connected with a second pump.

[0009] As a further implementation manner, the second pump is connected with the inlet of a condensate stripping tower.

[0010] As a further implementation manner, the bottom of the condensate stripping tower is connected with a reboiler.

[0011] As a further implementation manner, the top of the condensate stripping tower is connected with a condenser, and the condenser is connected with a benzene-water separator.

[0012] In a second aspect, embodiments of the present application also provide a benzene residue recovery method, and the specific steps are as follows:

[0013] The wastewater flowing out of the first benzene distillation column is introduced into the second distillation column;

[0014] The desalted water is introduced into the second distillation column to dilute the wastewater;

[0015] The dilute solution exceeding the fixed liquid level in the second distillation column is introduced into the condensate stripping column;

[0016] The dilute solution in the condensate stripping column is evaporated by the reboiler at the bottom, and after the steam is condensed, the benzene and water are completely separated by the benzene-water separator, and part of the benzene is recovered.

[0017] As a further implementation, after the dilute solution in the condensate stripping column is evaporated, the steam moves upward from the condenser stripping column, and is condensed by the condenser above the reboiler.

[0018] As a further implementation, after condensation, the benzene and water are separated by the benzene-water separator, part of the benzene is introduced into the benzene storage tank, and the other part of the benzene is introduced back into the condensate stripping column.

[0019] The present application has the following beneficial effects:

[0020] (1) The present application sets up a second benzene distillation column to dilute the wastewater, and the wastewater output from the first distillation column is diluted by injecting desalted water into the second benzene distillation column; the dilute solution flowing out of the second benzene distillation column is subjected to benzene recovery by the condensate stripping column, without the need for traditional direct output of the residue in the second benzene distillation column to the residual benzene tank for treatment by external mechanisms.

[0021] (2) The present application recovers benzene by the second benzene distillation column existing in the benzene extraction process itself, without the need for any additional external equipment, without the need for recovery by outputting the residual benzene tank, and the benzene recovered by the second benzene distillation column can be directly used in the benzene extraction process to achieve recycling. BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the description of the exemplary embodiments of the present application and their explanation serve to explain the present application, and do not constitute an improper limitation of the present application.

[0023] Figure 1 is a benzene residue recovery system flowchart according to one or more embodiments of the present application;

[0024] In the figure, 1. first benzene distillation column, 2. first pump, 3. second distillation column, 4. second pump, 5. condensate stripping column, 6. condenser stripping column cooler, 7. benzene water separator, 8. crude benzene tank, 9. condensate stripping column discharge pump, 10. waste water concentration station, 11. caprolactam extraction column, 12. caprolactam extraction column bottom pump, 13. residual benzene tank. DETAILED DESCRIPTION

[0025] Example One

[0026] The example provides a benzene residue recovery system, which comprises a first benzene distillation column, desalted water and waste water flowing out of the first benzene distillation column flow through the second benzene distillation column after dilution and flow into the condensate stripping column to recover benzene.

[0027] The outlet of the first benzene distillation column 1 is connected with the first pump 2. The first pump 2 is connected with the inlet of the second distillation column 3. The outlet of the second distillation column 3 is connected with the second pump 4. The second pump 4 is connected with the inlet of the condensate stripping column 5. The condensate stripping column 5 is connected with the condenser above the reboiler in the condensate stripping column 5. The condenser is connected with the benzene water separator 7.

[0028] The first pump 2 is a first benzene distillation column kettle pump with a model of P7316, which is used to pump the waste water in the first benzene distillation column 1 into the second benzene distillation column 3. The desalted water flows into the second benzene distillation column through the water inlet pipe of the second benzene distillation column 3. The second pump 4 is a second benzene distillation column kettle pump with a model of P7304-44, which is used to flow the diluted waste water in the second benzene distillation column 3 into the condensate stripping column 5.

[0029] The condensate stripping column 5 is connected with the condenser stripping column cooler 6. The condensate stripping column 5 cooler is connected with the benzene water separator 7. The benzene water separator 7 is connected with the crude benzene tank 8.

[0030] The condensate stripping column 5 is connected with the condensate stripping column discharge pump 9. The condensate stripping column discharge pump 9 is connected with the waste water concentration station 10.

[0031] The caprolactam extraction column 11 is connected with the caprolactam extraction column bottom pump 12. The caprolactam extraction column bottom pump 12 is connected with the condensate stripping column 5.

[0032] The dilution wastewater in the condensate stripping tower 5 is transported to the wastewater concentration station by a condensate stripping tower discharge pump. In the caprolactam extraction process, the benzene extract liquid is input into the condensate stripping tower 5 by a caprolactam extraction tower bottom pump connected to a P7308 caprolactam extraction tower, and is transported into the condensate stripping tower 5 together with the dilution wastewater in the second benzene distillation tower, and then is transported to the wastewater concentration station by a condensate stripping tower discharge pump connected to the condensate stripping tower 5. The C7306 condensate stripping tower functions as follows: the condensate cooled by a condensate stripping tower cooler (E7315) is discharged to a benzene-water separator (S7323), the water layer separated is discharged to the condensate stripping tower 5 (C7306) to strip benzene therefrom, and the benzene layer is discharged to a crude benzene tank (T27109).

[0033] Further, the C7302 caprolactam extraction tower functions to remove impurities from the caprolactam aqueous solution, and separates an aqueous solution containing organic impurities and ammonium sulfate for wastewater treatment.

[0034] In the embodiment, the second benzene distillation tower bottom pump is connected to the condensate stripping tower 5 instead of the residual benzene tank 13, and benzene is recycled by the condensate stripping tower 5. Part of the benzene flows back into the condensate stripping tower 5, and the other part is separated from water by a benzene-water separator and then is recycled into the crude benzene tank.

[0035] Embodiment two:

[0036] The embodiment provides a benzene residue recycling method. In a traditional benzene recycling method, the benzene residue is sent to a residual benzene tank (T27131) to be closed, and is instead sent into a condensate stripping tower (C7306) to recycle benzene therefrom, and materials that cannot be treated are sent to a wastewater concentration process for treatment. In the embodiment, a benzene residue recycling method is used, and benzene is not recycled by an external mechanism, but is recycled by improving the benzene extraction system itself. The specific steps are as follows:

[0037] Step 1: The wastewater flowing out of the first benzene distillation tower 1 is input into the second distillation tower 3.

[0038] Step 2: The desalted water is input into the second distillation tower 3 to dilute the wastewater.

[0039] Further, a desalted water is added to the feed pipe, so that the material input into the second distillation tower 3 is diluted, and the condition of forming a benzene-water azeotrope is met, which is more conducive to recycling benzene by the second distillation tower 3.

[0040] By adding a desalted water line to the pipe from the first pump 2 (model P7316) to the second distillation column 3 (model C7304-4), the flow of desalted water is similar to the flow of the first pump 2, and the steam flow of the reboiler at the bottom of the second distillation column 3 (model C7304-4) is increased to maintain the bottom temperature at 95-100°C, ensuring that water cannot be directly evaporated.

[0041] Step 3: The dilute solution in the second distillation column 3 above the fixed level flows into the condensate stripping column 5.

[0042] Further, the desalted water input from the first pump 2 to the second distillation column 3 is intermittently delivered, and when the dilute solution in the second distillation column 3 exceeds the fixed water level, the dilute solution in the second distillation column 3 is continuously delivered to the condensate stripping column.

[0043] Further, as the processing load of the condensate stripping column 5 increases, it is necessary to prevent the risk of overpressure or liquid blocking; the liquid level is controlled to maintain 45-55%, ensuring stable flow of the second pump (model P7304-44) to the condensate stripping column, while closely monitoring changes in the temperature and pressure of the condensate stripping column; ensure stable operation of the condensate stripping column 5, and immediately stop the residual benzene feed if overpressure is found; if liquid blocking occurs, a soft water inlet should be added at the inlet of the pump (model P7308) at the bottom of the condensate stripping column 5 to flush the condensate stripping column 5 and relieve the liquid blocking.

[0044] Step 4: The dilute solution in the condensate stripping column 5 is evaporated by the reboiler at the bottom, and after the steam is condensed, the benzene and water are completely separated by the benzene-water separator, and part of the benzene is recovered.

[0045] Further, after the dilute solution in the condensate stripping column 5 is evaporated, the steam moves upward from the condenser stripping column 5 and is condensed by the condenser above the reboiler.

[0046] Further, after condensation, the benzene and water are separated by the benzene-water separator, part of the benzene flows into the benzene storage tank, and the other part of the benzene flows back into the condensate stripping column.

[0047] Further, the operation of the discharge pump (model P7325) at the bottom of the condensate stripping column 5 is closely monitored, and the change in the pressure at the top of the condensate stripping column 5 is also noted; the control room personnel closely monitor the operating current and outlet pressure of the condensate stripping column discharge pump, and also monitor the flow changes of the condensate stripping column valve (model FIQ7850-3); if abnormalities occur, the pump should be reversed immediately, the cause should be identified and treated; the control room closely monitors the changes in the pressure at the top of the condensate stripping column, and if overpressure is found, the condenser should be cleaned with steam in a timely manner.

[0048] Further, the condensate stripping column 5 sends the waste water to the waste water concentration station by a condensate discharge pump, the dilute solution in the condensate stripping column 5 is evaporated by a reboiler in the condensate stripping column 5, and the steam is cooled by a cooler at the top, the cooled liquid is separated by a benzene water separator, and part of the benzene is recovered to the condensate stripping column 5 for the benzene extraction process, and the other part of the benzene is sent to a crude benzene tank by the benzene water separator for collection and reuse.

[0049] Further, the material sent to the waste water concentration station changes, the organic matter increases, and attention should be paid to the material foaming in the waste water evaporation chamber, which affects the operation of the waste water MVR fan; the on-site personnel maintain the addition of a defoaming agent at the axial flow pump of the evaporation tower, and add it in time for inspection, to prevent the material from foaming and affecting the operation of the MVR fan.

[0050] Through the method in the embodiment, the benzene in the benzene residue can be recovered, the remaining residue can be treated, and good economic benefits can be achieved. The economic benefits are as follows:

[0051] ①The amount of benzene residue treated by a third party is 78 tons / month, the cost of treating 1 ton of benzene residue is 3500 yuan / ton, and the monthly savings in treatment cost is: 78 tons x 3500 yuan / month / ton = 273 (thousand yuan / month).

[0052] ②The amount of recovered benzene is 78 tons x 40% (benzene content) = 31.2 tons, and the monthly value of recovered benzene is: 31.2 tons x 9000 yuan / ton = 280800 (yuan)

[0053] Total: The monthly savings are about 553800 (yuan)

[0054] The total annual savings are 6645600 (yuan)

[0055] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various changes and modifications to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A benzene residue recovery system, characterized in that, The first benzene distillation tower contains demineralized water and wastewater that flow out of the first benzene distillation tower. After being diluted by the second benzene distillation tower, the wastewater flows into the condensate stripping tower to recover benzene. The demineralized water flows into the second benzene distillation tower through the inlet pipe. The demineralized water pumped into the second distillation column is delivered intermittently. Only when the diluted solution in the second distillation column exceeds a fixed water level is the diluted solution continuously fed into the condensate stripping column.

2. The benzene residue recovery system as described in claim 1, characterized in that, The outlet of the first benzene distillation column is connected to the first pump.

3. The benzene residue recovery system as described in claim 1, characterized in that, The first pump is connected to the inlet of the second distillation column.

4. The benzene residue recovery system as described in claim 1, characterized in that, The outlet of the second distillation column is connected to the second pump.

5. A benzene residue recovery system as described in claim 1, characterized in that, The second pump is connected to the inlet of the condensate stripping tower.

6. A benzene residue recovery system as described in claim 1, characterized in that, A reboiler is connected to the bottom of the condensate stripping tower.

7. A benzene residue recovery system as described in claim 1, characterized in that, The top of the condensate stripping tower is connected to a condenser, which is connected to a benzene-water separator.

8. A method for recovering benzene residue, characterized in that, The benzene residue recovery system according to any one of claims 1-7 comprises the following specific steps: The wastewater flowing out of the first benzene distillation tower enters the second distillation tower; The demineralized water flows into the second distillation tower to dilute the wastewater; The diluted solution in the second distillation column that exceeds the fixed liquid level flows into the condensate stripping column; The diluted solution in the condensate stripping tower is evaporated through the reboiler at the bottom. After the steam is condensed, benzene and water are completely separated through a benzene-water separator, and some of the benzene is recovered.

9. The method for recovering benzene residue as described in claim 8, characterized in that, After the diluted solution is evaporated in the condensate stripping tower, the steam moves upward from the condenser stripping tower and is condensed in the condenser above the reboiler.

10. The method for recovering benzene residue as described in claim 8, characterized in that, After condensation, benzene and water are separated by the benzene-water separator. Part of the benzene flows into the benzene storage tank, and the other part flows back into the condensate stripping tower.

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