Process for removing COD (Chemical Oxygen Demand) in evaporative condensate of POSM (Polyhedral Oligomeric

Abstract

The invention relates to a process for removing COD (Chemical Oxygen Demand) in evaporative condensate of POSM (Polyhedral Oriented Sodium Methyl) waste alkali liquor, belonging to the technical field of wastewater treatment. A first-effect alkali liquor circulating pump, a second-effect alkali liquor circulating pump and a third-effect alkali liquor circulating pump are respectively arranged at first-section filler layers of a first-effect flash separation tower, a second-effect flash separation tower and a third-effect flash separation tower; liquid caustic soda is added into a separation reaction section of a flash separation tower, in the separation reaction section, the liquid caustic soda reacts with phenol in rising steam to generate sodium phenolate, sodium phenolate and salt substances, the boiling point is high, the physical properties are changed, the substances fall back into tower kettle liquid again, benzene series substances such as methyl benzyl alcohol and phenethyl alcohol carried by the phenol can be separated out due to the fact that an azeotropic system is damaged, and the content of the benzene series substances is reduced. The multiple-effect condensate is transferred into the tower kettle liquid, so that the benzene series in the multiple-effect condensate is greatly reduced compared with a system without adding the liquid alkali, the concentration of the material in the feeding of the rectifying tower can be reduced, and the content of the benzene series in the tower kettle liquid is reduced after the multiple-effect condensate is separated by the rectifying tower.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment and relates to a COD removal process for evaporation condensate of POSM waste lye. BACKGROUND

[0002] In industry, propylene oxide (PO) is often produced by co-oxidation method to co-produce styrene (SM). A large amount of waste lye is generated in the production of propylene oxide and styrene. The waste lye is relatively complex in composition and mainly includes propylene oxide, acetophenone, benzaldehyde, 2-ethylphenol, 3-ethylphenol, methylbenzyl alcohol, ethylbenzene, phenethyl alcohol and other substances. The waste water has high COD concentration and high benzene series concentration. Since the heat value is low, direct incineration treatment will consume a large amount of fuel and has high cost.

[0003] Chinese patent application with publication number CN115594611A discloses a method for recovering phenol in p-hydroxybenzonitrile wastewater by extractive distillation. The method extracts phenol in the wastewater by extractive distillation. The method needs an extractant, a distillation column reaction equipment and steam energy in later operation. The process requires large investment in reagents and process equipment, has high cost in later operation, is complex and requires many operating personnel.

[0004] Chinese patent application with publication number CN106220527A discloses a DMF distillation dehydration purification method. The method uses a three-effect concentration process + distillation to treat wastewater. The method does not treat phenol in the wastewater, resulting in high phenol content in the three-effect concentration condensate. The condensate enters the distillation column, phenol and water form azeotrope, resulting in excessive COD and benzene series in the distillation column condensate.

[0005] Chinese patent application with publication number CN119191416A discloses a POSM waste lye concentration process and device. The process is a “three-effect forced circulation evaporation + stripping” process. The waste lye is first concentrated by countercurrent multi-effect evaporation, and the evaporation condensate is further reduced in COD by stripping. The device includes a three-effect evaporation tower, a two-effect evaporation tower, a one-effect evaporation tower and a stripping tower. The evaporation separation chamber is provided with separation filler and a condenser. Stripping uses pressurized distillation. The backflow tank has phase separation capacity, can realize separation of organic phase and water phase, is provided with a heat exchanger for heat coupling between the gas phase at the top of the stripping tower and the evaporation concentrated feed, reduces energy consumption, effectively reduces the COD value of the evaporation condensate and improves the concentration ratio of the waste lye. However, no specific solution is designed for the azeotropic properties of phenol and water in the POSM waste lye, resulting in possible residual phenol and associated benzene series in the evaporation condensate.

[0006] The 2-ethyl phenol and 3-ethyl phenol contained in the wastewater exist in the form of phenolate in an alkaline environment, and are decomposed by heat to produce phenol when multi-effect concentration, the phenol forms azeotrope with water to enter the gas phase, part of which is transferred with the condensate, and under acidic conditions, it can carry benzyl alcohol, phenethyl alcohol and other benzene series substances, resulting in complex azeotrope composition and high concentration in the condensate; after these substances enter the rectifying column, the azeotrope system is difficult to separate from water, most of which remains in the column bottom liquid, causing the benzene series and COD to exceed the standard, which cannot meet the requirements of biochemical influent; at the same time, the methyl benzyl alcohol and phenethyl ketone formed by condensation of the vapor at the top of the rectifying column are not soluble in water, part of which returns to the tower and blocks the packing, reduces the mass transfer efficiency, increases the equipment maintenance frequency, and part of which enters the column bottom liquid, also causes the oil and COD to exceed the standard. SUMMARY

[0007] The purpose of the present application is to provide a kind of POSM waste lye evaporation condensate COD removal process, by setting alkali device in the first stage packing layer of flash separation tower, destroy azeotrope system, then separate by rectifying column, stripping column, reach the effect of reducing benzene series in waste lye.

[0008] The purpose of the present application can be realized by the following technical solutions: A kind of POSM waste lye evaporation condensate COD removal process, comprising the following steps: Step one: the POSM waste lye is sent to primary raw material preheater, secondary raw material preheater for preheating by pressure reducing valve, then is transported to one effect flash separation tower for evaporation concentration, the top of the first stage packing of one effect flash separation tower is provided with alkali liquid inlet and alkali liquid outlet, and one effect alkali liquid circulating pump is arranged at the alkali liquid outlet, the alkali liquid is sprayed on the top of one effect flash separation tower and reacts with the tower top vapor on the packing.

[0009] Step two: the waste liquid separated from one effect flash separation tower is transported to two effect flash separation tower for evaporation concentration by one effect discharge pump, two effect alkali liquid circulating pump is arranged at the alkali liquid outlet of two effect flash separation tower, and the separated waste liquid is transported to three effect flash separation tower for evaporation concentration by two effect discharge pump, and three effect alkali liquid circulating pump is arranged at the alkali liquid outlet of three effect flash separation tower.

[0010] Step three: the secondary vapor separated from two effect flash separation tower and three effect flash separation tower is transported to secondary vapor condensate tank, preheated by preheater and then enters rectifying column for purification, the waste liquid at the bottom of rectifying column is heated by reboiler and enters stripping column, the separated waste liquid is cooled and discharged to the outside, the gas at the top of stripping column is cooled, then oil-water separation is carried out to obtain water phase and oil phase, and the oil phase is discharged to the outside.

[0011] Further, the alkali liquid inlet is provided with feed regulating valve and pH meter, and the pH value is controlled to maintain at 13-14.

[0012] Further, a first circulating pump is arranged at the bottom of the first flash separation tower, and part of the waste liquid is delivered to the first heating chamber by the first circulating pump for heating, and the waste liquid flow is 272.7-282.7 t / h, and after heating, the waste liquid enters the first flash separation tower for gas-liquid separation.

[0013] Further, a second circulating pump is arranged at the bottom of the second flash separation tower, and part of the waste liquid is delivered to the second heating chamber by the second circulating pump for heating, and the waste liquid flow is 227.8-229.8 t / h, and after heating, the waste liquid enters the second flash separation tower for gas-liquid separation.

[0014] Further, a third circulating pump is arranged at the bottom of the third flash separation tower, and part of the waste liquid is delivered to the third heating chamber by the third circulating pump for heating, and the waste liquid flow is 269.25-279.25 t / h, and after heating, the waste liquid enters the third flash separation tower for gas-liquid separation.

[0015] Further, the temperature of the POSM waste lye is 43-45℃, and the pressure is 1.20-1.40 MPaG, and the pressure of the waste lye is reduced to 0.4 MPaG by the pressure reducing valve; the flow of the POSM waste lye is 272.7-282.7 t / h.

[0016] Further, the temperature of the secondary steam condensate in the first flash separation tower is 70-76℃, the pressure is 500-540 KPaG, and the flow is 0.98-1.02 t / h.

[0017] Further, the temperature of the secondary steam condensate in the second flash separation tower is 70-76℃, the pressure is 500-540 KPaG, and the flow is 1.08-1.18 t / h.

[0018] Further, the temperature of the secondary steam condensate in the third flash separation tower is 70-80℃, the pressure is 500-560 KPaG, and the flow is 1.22-1.32 t / h.

[0019] Further, the flow of the waste liquid in the rectification tower is 28.35-30.35 t / h.

[0020] Further, the waste liquid at the bottom of the stripping tower is cooled to 65-69℃ by the evaporation primary raw material preheater, and then cooled to 40-44℃ by the tower kettle cooler, the pressure is 0.6-0.7 MPaG, and the flow is 27.57-29.57 t / h.

[0021] Further, the overhead gas of the stripping tower is cooled to 95-102℃ by the overhead secondary raw material preheater, and then cooled to 42-45℃ by the stripping tower overhead liquid cooler.

[0022] Further, the temperature of the stripping tower overhead gas is 126-130 DEG C, the pressure is 0.15-0.17 MPaG, and the flow rate is 4-6 t / h.

[0023] Further, a part of the water phase is delivered to the rectifying tower by a reflux pump as the overhead reflux liquid, and the flow rate is 3.22-4.22 t / h, and another part is discharged.

[0024] Further, the heat source of the first-stage raw material preheater is the tower kettle liquid of the rectifying tower, and the heat source of the second-stage raw material preheater is the overhead gas of the rectifying tower.

[0025] The "G" in unit MPaG and KPaG represents gauge pressure, i.e., the pressure indicated by a pressure gauge.

[0026] The beneficial effects of the present application are: 1、The present application sets a one-effect lye circulating pump, a two-effect lye circulating pump and a three-effect lye circulating pump at the first-stage packing layer of the one-effect flash separation tower, the two-effect flash separation tower and the three-effect flash separation tower respectively, constructs a closed-loop caustic washing system, and through the operation of the circulating pump, liquid caustic is added to the separation reaction section of the flash separation tower, in the separation reaction section, the liquid caustic reacts with phenol in the rising steam to generate sodium phenate, the sodium phenate and salt substances change in physical properties due to the higher boiling point, 2-ethyl phenol and 3-ethyl phenol react to generate 2-ethyl phenol sodium and 3-ethyl phenol sodium and fall back to the tower kettle liquid, thus the methyl benzyl alcohol, phenethyl alcohol and other benzene series substances carried by the phenol due to the destruction of the azeotropic system are transferred to the tower kettle liquid, so that the 2-ethyl phenol, 3-ethyl phenol, methyl benzyl alcohol and phenethyl alcohol in the multi-effect condensate are greatly reduced compared with the system without adding liquid caustic, thus the concentration of the substances in the rectifying tower feed is reduced, the benzene series content in the tower kettle liquid after the multi-effect condensate is separated by the rectifying tower is reduced, and the COD can meet the requirement of biochemical influent.

[0027] 2、The present application respectively sets a filler layer in a single-effect flash separation tower, a double-effect flash separation tower and a triple-effect flash separation tower, sets a washing liquid at the top of the tower, uses the condensed liquid at the top of the tower as the washing liquid, carries out countercurrent contact and mass transfer between the rising steam in the reaction section in the tower and the washing liquid, makes the heavy components carried by the mist in the liquid at the top of the flash separation tower pass into the washing liquid after being washed, further reduces the heavy components in the flash separation tower, reduces the load of the feed in the subsequent rectification section, compared with the process without the filler layer, achieves the same separation effect, the previous process can reduce the steam consumption of the reboiler, reduces the height of the filler layer, saves energy and reduces consumption, reduces investment and operation cost, in addition, liquid alkali is added in the tower, the liquid alkali reacts with the rising steam in the filler layer, the setting of the filler layer can increase the contact area of the liquid alkali and the rising steam, enhance the mass transfer, prolong the reaction time, make the liquid alkali fully react with the rising steam, reduce the addition amount of the alkali liquid, if the filler layer is not set, the addition amount of the liquid alkali increases, causes the liquid alkali to scale in the equipment cylinder, reduces the working efficiency of the flash separation tower, increases the maintenance time and frequency, reduces the equipment operation stability.

[0028] 3、The condensed steam at the top of the stripping tower is liquid, the liquid is oil-water two-phase, high-efficiency oil-water separation is realized through a phase separation tank, a large amount of benzene series such as methylbenzyl alcohol, phenylacetone, phenylethanol and other benzene series substances are contained in the oil phase, the COD is high, continuous separation is carried out to the boundary, oil substances are avoided to return to the rectifying tower reflux, equipment blockage is prevented, equipment operation stability is ensured, in addition, the separation of oil substances can make high-COD substances and benzene series move to the outside of the tower, do not participate in reflux and reboiling, ensure that the COD and benzene series in the tower bottom liquid meet the discharge standard. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a process flow chart of the COD removal process of the evaporation and condensation liquid of the POSM waste alkali liquid of the present application. Figure 2 It is a structure schematic view of the single-effect flash separation tower in embodiment 1 of the present application.

[0030] Attached reference numerals: 1. Pressure reducing valve; 2. Primary feed preheater; 3. Secondary feed preheater; 4. First-effect flash separation tower; 5. First-effect circulating pump; 6. First-effect heating chamber; 7. First-effect alkali circulating pump; 8. Feed regulating valve; 9. pH meter; 10. First-effect discharge pump; 11. Second-effect flash separation tower; 12. Second-effect alkali circulating pump; 13. Second-effect circulating pump; 14. Second-effect heating chamber; 15. Second-effect discharge pump; 16. Third-effect flash separation tower; 17. Third-effect concentrator pump; 18. Third-effect circulating pump; 19. Third-effect heating chamber; 20. Third-effect alkali circulating pump; 21. Second-effect balance tank; 2. Air cooler; 23. Secondary steam condensate tank; 24. Secondary steam condensate pump; 25. Preheater; 26. Distillation column; 27. Reboiler; 28. Reflux pump; 29. ​​Stripping column; 30. Top secondary feed preheater; 31. Stripping column top liquid cooler; 32. Phase separation tank; 33. Skimming tank; 34. Skimming pump; 35. Evaporation primary feed preheater; 36. Reboiler cooler; 401. Alkali washing liquid inlet; 402. Secondary steam outlet; 403. Alkali washing liquid outlet; 404. Circulating liquid inlet; 405. Material inlet; 406. Steam inlet; 407. Circulating liquid outlet. Detailed Implementation

[0031] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0032] Example 1: This example provides a COD removal process for the evaporation condensate of POSM waste alkaline solution. Please refer to [link / reference]. Figure 1 It includes the following steps: S1: the POSM waste lye with a temperature of 43℃ and a pressure of 1.20 MPaG (G means gauge pressure) is decompressed by a pressure reducing valve 1, the pressure drop of the waste lye is 0.4 MPaG, enters a first-stage raw material preheater 2 and is preheated to 77℃, the heat source of the first-stage raw material preheater 2 is the column still liquid of a rectifying tower 26, then is preheated to 118℃ by a second-stage raw material preheater 3, the heat source of the second-stage raw material preheater 3 is the overhead vapor of the rectifying tower 26, then enters a first-stage flash separation tower 4 for evaporation concentration, a first-stage circulating pump 5 is arranged at the bottom of the first-stage flash separation tower 4, a part of the POSM waste lye is transported to a first-stage heating chamber 6 for heating, the flow of the POSM waste lye is 272.7 t / h, the heat source of the first-stage heating chamber 6 is live steam (150℃, 0.29 MPaG, 11.08 t / h), after heating, the POSM waste lye becomes gas-liquid two-phase, enters the first-stage flash separation tower 4 for gas-liquid separation, at the same time, the secondary steam (123℃, 92 KPaG, 9.93 t / h) generated by the first-stage heating chamber 6 can be used as the heat source of a second-stage heating chamber 14, 3 segments of packing layers are arranged at the upper part of the first-stage flash separation tower 4, the secondary steam flashed out of the first-stage flash separation tower 4 contacts with the secondary steam condensate (70℃, 500 KPaG, 0.98 t / h) at the packing layers, mass transfer, the heavy components of the rising steam are transferred to the liquid phase, the heavy component concentration in the overhead liquid of the first-stage flash separation tower 4 is further reduced, an alkali lye outlet 403 is arranged at the lower part of the first segment of packing layers at the upper part of the first-stage flash separation tower 4, an alkali lye inlet 401 is arranged at the upper part of the first segment of packing layers, and a first-stage alkali lye circulating pump 7 is arranged at the alkali lye outlet 403, the inlet pipeline of the first-stage alkali lye circulating pump 7 is connected with the alkali lye outlet 403, the outlet pipeline of the first-stage alkali lye circulating pump 7 is connected with the alkali lye inlet 401, the alkali lye inlet 401 is further provided with a feed adjusting valve 8 and a pH meter 9, the pH value is controlled by controlling the opening degree of the feed adjusting valve 8, and the pH value is maintained at about 13, the alkali lye is sprayed in the first-stage flash separation tower 4 by the operation of the first-stage alkali lye circulating pump 7, the alkali lye (sodium hydroxide solution) reacts with the overhead vapor of the first-stage flash separation tower 4 at the packing layers, the overhead gas is neutralized to be alkali lye gas, and the circulation amount is 10 t / h.

[0033] Please refer to Figure 2 The first-stage flash separation tower 4 is provided with a secondary steam outlet 402 at the top, the alkali lye inlet 401 is arranged at the upper part of the first segment of packing layers, and the alkali lye outlet 403 is arranged at the lower part of the first segment of packing layers, the alkali lye (sodium hydroxide solution) enters the tower from the alkali lye inlet 401, then enters the first-stage alkali lye circulating pump 7 for circulation from the alkali lye outlet 403, the first-stage flash separation tower 4 is provided with a circulating liquid outlet 407 at the bottom, a steam port 406 is arranged above the circulating liquid outlet 407, a circulating liquid inlet 404 and a material feed port 405 are arranged above the steam port 406.

[0034] S2: The waste liquid separated from the first-stage flash separation tower 4 is sent to the second-stage flash separation tower 11 for evaporation and concentration by a first-stage discharge pump 10. The bottom of the second-stage flash separation tower 11 is provided with a second-stage circulating pump 13. The second-stage circulating pump 13 sends a portion of the waste liquid to the second-stage heating chamber 14 at a flow rate of 227.8 t / h. The heat source of the second-stage heating chamber 14 is the secondary steam (123℃, 92KPaG, 9.93t / h) of the first-stage heating chamber 6. After being heated, the waste liquid becomes a gas-liquid two-phase, enters the second-stage flash separation tower 11 for gas-liquid separation, and at the same time, the secondary steam (106℃, 21KPaG, 10.54t / h) generated by the second-stage heating chamber 14 is used as the heat source of the third-stage heating chamber 19. The secondary steam of the second-stage flash separation tower 11 is condensed and enters the second-stage balance tank 21, and finally enters the secondary steam condensate tank 23. The upper part of the second-stage flash separation tower 11 is provided with 3 stages of packing layers. The secondary steam flashed out of the second-stage flash separation tower 11 contacts with the secondary steam condensate (70℃, 500KPaG, 1.08t / h) refluxed from the top in the packing layer, mass transfer, and the heavy components of the rising steam are transferred to the liquid phase, further reducing the concentration of heavy components in the liquid at the top of the second-stage flash separation tower 11. The lower part of the first stage of packing of the second-stage flash separation tower 11 is provided with an alkali washing liquid outlet 403, and the upper part of the first stage of packing is provided with an alkali washing liquid inlet 401. The alkali washing liquid outlet 403 is provided with a second-stage alkali liquid circulating pump 12. The inlet pipeline of the second-stage alkali liquid circulating pump 12 is connected with the alkali washing liquid outlet 403, and the outlet pipeline of the second-stage alkali liquid circulating pump 12 is connected with the alkali washing liquid inlet 401. The alkali washing liquid inlet 401 is also provided with a feed regulating valve 8 and a pH meter 9. The opening degree of the feed regulating valve 8 is controlled to control the pH value, which is maintained at about 13. The alkali washing liquid is sprayed on the top of the second-stage flash separation tower 11 by the operation of the second-stage alkali liquid circulating pump 12. The alkali washing liquid reacts with the gas at the top of the second-stage flash separation tower 11 to neutralize the gas into alkali gas, and the circulation amount is 10 t / h.

[0035] S3: The waste liquid separated from the two-effect flash separation tower 11 is delivered to the three-effect flash separation tower 16 for evaporation and concentration by a two-effect discharge pump 15. A three-effect circulating pump 18 is arranged at the bottom of the three-effect flash separation tower 16. The three-effect circulating pump 18 delivers a portion of the waste liquid to a three-effect heating chamber 19 at a flow rate of 269.25 t / h. The heat source of the three-effect heating chamber 19 is the secondary steam (106°C, 21 KPaG, 10.54 t / h) generated by the two-effect heating chamber 14. After being heated, the waste liquid becomes a gas-liquid two-phase, enters the three-effect flash separation tower 16 for gas-liquid separation. The secondary steam (80°C, -54 KPaG, 11.653 t / h) separated from the three-effect flash separation tower 16 enters an air cooler 22 for cooling, and then enters a secondary steam condensate tank 23. The inlet of the air cooler 22 is connected with the secondary steam outlet 402 of the three-effect flash separation tower 16, and the outlet is connected with the inlet pipeline of the secondary steam condensate tank 23. The concentrated waste liquid is discharged outside by a three-effect concentration pump 17 at a flow rate of 26.2 t / h. A three-stage packing layer is arranged at the upper part of the three-effect flash separation tower 16. The secondary steam separated from the three-effect flash separation tower 16 contacts with the secondary steam condensate (70°C, 500 KPaG, 1.22 t / h) refluxed from the top in the packing layer for mass transfer. The heavy components of the rising steam are transferred to the liquid phase, further reducing the concentration of heavy components in the liquid at the top of the three-effect flash separation tower 16. An alkali washing liquid outlet 403 is arranged at the lower part of the first stage of packing at the top of the three-effect flash separation tower 16. An alkali washing liquid inlet 401 is arranged at the upper part of the first stage of packing. A three-effect alkali liquid circulating pump 20 is arranged at the alkali washing liquid outlet 403. The inlet pipeline of the three-effect alkali liquid circulating pump 20 is connected with the alkali washing liquid outlet 403. The outlet pipeline of the three-effect alkali liquid circulating pump 20 is connected with the alkali washing liquid inlet 401. The alkali washing liquid inlet 401 is further provided with a feed adjusting valve 8 and a pH meter 9. The opening degree of the feed adjusting valve 8 is controlled to control the pH value, which is maintained at about 13. The alkali washing liquid is sprayed in the three-effect flash separation tower 16 by the operation of the three-effect alkali liquid circulating pump 20. The alkali washing liquid reacts with the steam at the top of the three-effect flash separation tower 16 in the packing layer, so that the steam at the top is neutralized to alkali liquid gas. The circulation amount is 10 t / h.

[0036] S4: The liquid in the secondary steam condensate tank 23 is delivered to the one-effect flash separation tower 4, the two-effect flash separation tower 11 and the three-effect flash separation tower 16 as washing liquid by a secondary steam condensate pump 24. Another part of the liquid is delivered to a preheater 25 for preheating to 188°C, and then enters a rectifying tower 26 for purification at a flow rate of 28.35 t / h. The rectifying tower 26 is internally provided with packing. The waste liquid (128°C, 150 KPaG) at the bottom of the rectifying tower 26 enters a reboiler 27 (model E-12111) for heating. The heat source of the reboiler 27 is live steam (150°C, 0.29 MPaG, 4.9 t / h).

[0037] S5: After heating by reboiler 27, the waste liquid becomes gas-liquid two-phase, enters stripping column 29, and exchanges mass with the overhead liquid (42℃, 490KPaG, 3.83t / h) of stripping column 29. The heavy components contained in the rising steam are transferred to the liquid phase, and the light components in the overhead liquid of stripping column 29 are transferred to the gas phase. The light components are separated, and the heavy components are refined. The waste liquid at the bottom of stripping column 29 is cooled to 65℃ by evaporation primary raw material preheater 35 (E-12101), and then cooled to 40℃ (0.6MPaG) by column bottom cooler 36 (model E-12103), and discharged to the outside, with a flow rate of 27.57t / h.

[0038] S6: The overhead gas (126℃, 0.15MPaG, 4t / h) of stripping column 29 is cooled to 95℃ by overhead secondary raw material preheater 30, and then cooled to 42℃ by stripping column overhead liquid cooler 31, and then enters phase separation tank 32 for oil-water separation. The oil phase is discharged to oil skimming tank 33, transported to the outside by oil skimming pump 34, with a flow rate of 0.164t / h. The water phase is transported to rectifying column 26 as overhead reflux liquid by part of reflux pump 28, with a flow rate of 3.22t / h, and part of it is discharged to the outside, with a flow rate of 0.614t / h.

[0039] Example 2: The present example provides a process for removing COD from the evaporation condensate of POSM waste lye, comprising the following steps: S1: the POSM waste lye with a temperature of 45℃ and a pressure of 1.40MPaG is decompressed by a pressure reducing valve 1, the pressure drop of the waste lye is 0.4MPaG, and the waste lye is preheated to 80℃ in a first raw material preheater 2, the heat source of the first raw material preheater 2 is the column bottom liquid of a rectifying tower 26, and then the waste lye is preheated to 120℃ in a second raw material preheater 3, the heat source of the second raw material preheater 3 is the overhead vapor of the rectifying tower 26, and then the waste lye is evaporated and concentrated in a first flash separation tower 4, a first circulating pump 5 is arranged at the bottom of the first flash separation tower 4, a part of the waste lye is transported to a first heating chamber 6 for heating, the flow of the waste lye is 282.7t / h, the heat source of the first heating chamber 6 is live steam (150℃, 0.29MPaG, 11.08t / h), after heating, the waste lye becomes gas-liquid two-phase, enters the first flash separation tower 4 for gas-liquid separation, and the secondary steam (125℃, 98KPaG, 9.97t / h) generated by the first heating chamber 6 can be used as the heat source of a second heating chamber 14, 3 segments of packing layers are arranged at the upper part of the first flash separation tower 4, the secondary steam and the condensed liquid (76℃, 540KPaG, 1.02t / h) of the overhead reflux of the secondary steam in the packing layers are contacted, mass transfer is performed, the heavy components of the rising steam are transferred to the liquid phase, the concentration of the heavy components in the overhead liquid of the first flash separation tower 4 is further reduced, an alkali lye outlet 403 is arranged at the lower part of the first segment of packing layers of the first flash separation tower 4, an alkali lye inlet 401 is arranged at the upper part of the first segment of packing layers, and a first alkali lye circulating pump 7 is arranged at the alkali lye outlet 403, the inlet pipeline of the first alkali lye circulating pump 7 is connected with the alkali lye outlet 403, the outlet pipeline of the first alkali lye circulating pump 7 is connected with the alkali lye inlet 401, the alkali lye inlet 401 is further provided with a feed adjusting valve 8 and a pH meter 9, the opening degree of the feed adjusting valve 8 is controlled to control the pH value, and the pH value is maintained at about 13, the alkali lye is sprayed in the first flash separation tower 4 by the operation of the first alkali lye circulating pump 7, the alkali lye and the overhead vapor of the first flash separation tower 4 react in the packing layers, the overhead vapor is neutralized to be alkali vapor, and the circulation amount is 10t / h.

[0040] S2: The waste liquid separated from the first-stage flash separation tower 4 is sent to the second-stage flash separation tower 11 for evaporation and concentration by a first-stage discharge pump 10. The bottom of the second-stage flash separation tower 11 is provided with a second-stage circulating pump 13. The second-stage circulating pump 13 sends a portion of the waste liquid to the second-stage heating chamber 14 at a flow rate of 229.8 t / h. The heat source of the second-stage heating chamber 14 is the secondary steam (125°C, 100 KPaG, 9.97 t / h) of the first-stage heating chamber 6. After being heated, the waste liquid becomes a gas-liquid two-phase, enters the second-stage flash separation tower 11 for gas-liquid separation, and at the same time, the secondary steam (108°C, 27 KPaG, 10.64 t / h) generated by the second-stage heating chamber 14 is used as the heat source of the third-stage heating chamber 19. The secondary steam of the second-stage flash separation tower 11 is condensed and enters the second-stage balance tank 21, and finally enters the secondary steam condensate tank 23. The upper part of the second-stage flash separation tower 11 is provided with 3 stages of packing layers. The secondary steam flashed out of the second-stage flash separation tower 11 contacts with the secondary steam condensate (76°C, 540 KPaG, 1.18 t / h) refluxed from the top in the packing layer, mass transfer, and the heavy components of the rising steam are transferred to the liquid phase, further reducing the concentration of heavy components in the liquid at the top of the second-stage flash separation tower 11. The lower part of the first stage of packing of the second-stage flash separation tower 11 is provided with an alkali washing liquid outlet 403, and the upper part of the first stage of packing is provided with an alkali washing liquid inlet 401. The alkali washing liquid outlet 403 is provided with a second-stage alkali liquid circulating pump 12. The inlet pipeline of the second-stage alkali liquid circulating pump 12 is connected with the alkali washing liquid outlet 403, and the outlet pipeline of the second-stage alkali liquid circulating pump 12 is connected with the alkali washing liquid inlet 401. The alkali washing liquid inlet 401 is also provided with a feed regulating valve 8 and a pH meter 9. The opening degree of the feed regulating valve 8 is controlled to control the pH value, which is maintained at about 13. The alkali washing liquid is sprayed on the top of the second-stage flash separation tower 11 by the operation of the second-stage alkali liquid circulating pump 12. The alkali washing liquid reacts with the gas at the top of the second-stage flash separation tower 11 to neutralize the gas into alkali gas, and the circulation amount is 10 t / h.

[0041] S3: The waste liquid separated from the two-effect flash separation tower 11 is delivered to the three-effect flash separation tower 16 for evaporation and concentration by a two-effect discharge pump 15. The bottom of the three-effect flash separation tower 16 is provided with a three-effect circulating pump 18, which delivers a portion of the waste liquid to a three-effect heating chamber 19 at a flow rate of 279.25 t / h. The heat source of the three-effect heating chamber 19 is the secondary steam (108°C, 25 KPaG, 10.64 t / h) generated by the two-effect heating chamber 14. After being heated, the waste liquid becomes a gas-liquid two-phase, enters the three-effect flash separation tower 16 for gas-liquid separation, and the secondary steam (85°C, -54 KPaG, 11.853 t / h) separated from the three-effect flash separation tower 16 enters an air cooler 22 for cooling, then enters a secondary steam condensate tank 23. The inlet of the air cooler 22 is connected with the secondary steam outlet 402 of the three-effect flash separation tower 16, and the outlet is connected with the inlet pipeline of the secondary steam condensate tank 23. The concentrated waste liquid is discharged outside by a three-effect concentration pump 17 at a flow rate of 28.2 t / h. The upper part of the three-effect flash separation tower 16 is provided with three sections of packing layers. The secondary steam separated from the three-effect flash separation tower 16 contacts with the secondary steam condensate (80°C, 560 KPaG, 1.32 t / h) refluxed from the top in the packing layers for mass transfer. The heavy components of the rising steam are transferred to the liquid phase, further reducing the concentration of heavy components in the liquid at the top of the three-effect flash separation tower 16. The lower part of the first section of packing at the top of the three-effect flash separation tower 16 is provided with an alkali washing liquid outlet 403, and the upper part of the first section of packing is provided with an alkali washing liquid inlet 401. A three-effect alkali liquid circulating pump 20 is arranged at the alkali washing liquid outlet 403. The inlet pipeline of the three-effect alkali liquid circulating pump 20 is connected with the alkali washing liquid outlet 403, and the outlet pipeline of the three-effect alkali liquid circulating pump 20 is connected with the alkali washing liquid inlet 401. The alkali washing liquid inlet 401 is also provided with a feed adjusting valve 8 and a pH meter 9. The opening degree of the feed adjusting valve 8 is controlled to control the pH value, which is maintained at about 13. The alkali washing liquid is sprayed on the top of the three-effect flash separation tower 16 by the operation of the three-effect alkali liquid circulating pump 20. The alkali washing liquid reacts with the gas at the top of the three-effect flash separation tower 16 in the packing to neutralize the gas into alkali gas. The circulation amount is 10 t / h.

[0042] S4: The liquid in the secondary steam condensate tank 23 is delivered to the one-effect flash separation tower 4, the two-effect flash separation tower 11 and the three-effect flash separation tower 16 as washing liquid by a secondary steam condensate pump 24, and a portion of the liquid is delivered to a preheater 25 for preheating to 200°C, then enters a rectifying tower 26 for purification at a flow rate of 30.35 t / h. The rectifying tower 26 is internally provided with packing. The waste liquid (130°C, 160 KPaG) at the bottom of the rectifying tower 26 enters a reboiler 27 (model E-12111) for heating. The heat source of the reboiler 27 is live steam (150°C, 0.29 MPaG, 4.9 t / h).

[0043] S5: After heating by reboiler 27, the waste liquid becomes gas-liquid two-phase, enters the stripping column 29, and mass transfer is carried out with the stripping column 29 overhead liquid (46℃, 500KPaG, 3.93t / h). The heavy components contained in the rising steam are transferred to the liquid phase, and the light components in the stripping column 29 overhead liquid are transferred to the gas phase. The light components are separated, and the heavy components are refined. The waste liquid at the bottom of the stripping column 29 is cooled to 69℃ by evaporation of the first-stage raw material preheater 35 (E-12101), and then cooled to 44℃ (0.7MPaG) by the column bottom cooler 36 (model E-12103). The flow rate is 29.57t / h.

[0044] S6: The stripping column 29 overhead gas (130℃, 0.17MPaG, 6t / h) is cooled to 102℃ by the second-stage raw material preheater 30 at the top of the column, and then cooled to 45℃ by the stripping column overhead liquid cooler 31 before entering the phase separation tank 32 for oil-water separation. The oil phase is discharged to the oil skimming tank 33, transported to the outside by the oil skimming pump 34, and the flow rate is 0.184t / h. The water phase is transported to the rectifying column 26 as the overhead reflux liquid by part of the reflux pump 28, and the flow rate is 4.22t / h. Part of the water phase is discharged to the outside 0.714t / h.

[0045] The alkali washing solution used in Examples 1-2 is a sodium hydroxide solution with a concentration of 8wt%.

[0046] Comparative Example 1: This comparative example provides a process for removing COD from the evaporation condensate of POSM waste alkali solution, which uses a traditional process (three-effect + rectification) to treat the waste alkali solution.

[0047] The wastewater treated by the processes of Examples 1-2 and Comparative Example 1 is tested, and the test results are as follows: Table 1 Comparison of treatment effect data

[0048] As can be seen from Table 1, the COD content and benzene series content in the wastewater treated by the removal processes of Examples 1 and 2 are lower than those of Comparative Example 1. This shows that the COD and benzene series of the waste alkali solution treated by the processes of Examples 1-2 are significantly lower than the requirements for biochemical influent (benzene series ≤50ppm, COD ≤4000ppm). Compared with the traditional three-effect + rectification process, it is proved that the improved process has obvious advantages in treating POSM waste alkali solution.

[0049] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, as long as the changes or modifications do not deviate from the technical solution of the present application. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application still belong to the scope of the technical solution of the present application.

Claims

1. A process for the removal of COD from the evaporation condensate of POSM spent caustic, characterized in that, The process comprises the following steps: Step one: the POSM waste lye is sent to a first-stage raw material preheater and a second-stage raw material preheater through a pressure-reducing valve for preheating, and then is delivered to a first-stage flash separation tower for evaporation and concentration, wherein an alkali lye inlet and an alkali lye outlet are respectively arranged at the upper part and the lower part of the first-stage flash separation tower, and a first-stage lye circulating pump is arranged at the alkali lye outlet, the alkali lye is sprayed on the top of the first-stage flash separation tower and reacts with the overhead vapor on the packing; Step two: the waste lye separated from the first-stage flash separation tower is delivered to a second-stage flash separation tower through a first-stage discharge pump for evaporation and concentration, a second-stage lye circulating pump is arranged at the alkali lye outlet of the second-stage flash separation tower, and the separated waste lye is delivered to a third-stage flash separation tower through a second-stage discharge pump for evaporation and concentration, and a third-stage lye circulating pump is arranged at the alkali lye outlet of the third-stage flash separation tower; Step three: the secondary steam separated from the second-stage flash separation tower and the third-stage flash separation tower is delivered to a secondary steam condensate tank, preheated by a preheater, and then enters a rectification tower for purification, the waste lye at the bottom of the rectification tower is heated by a reboiler and enters a stripping tower, the separated waste lye is cooled and discharged to the outside, and the gas at the top of the stripping tower is cooled, then is separated into water phase and oil phase by oil-water separation, and the oil phase is discharged to the outside.

2. The process for COD removal from evaporation condensate of POSM spent caustic as claimed in claim 1 wherein, A feed regulating valve and a pH meter are arranged at the alkali lye inlet in step one, and the pH value is controlled to be maintained at 13-14.

3. The process for COD removal from evaporated condensate of POSM spent caustic as claimed in claim 1 wherein, A first-stage circulating pump is arranged at the bottom of the first-stage flash separation tower, part of the waste lye is delivered to a first-stage heating chamber through the first-stage circulating pump for heating, the waste lye flow rate is 272.7-282.7 t / h, and after heating, the waste lye enters the first-stage flash separation tower for gas-liquid separation; A second-stage circulating pump is arranged at the bottom of the second-stage flash separation tower, part of the waste lye is delivered to a second-stage heating chamber through the second-stage circulating pump for heating, the waste lye flow rate is 227.8-229.8 t / h, and after heating, the waste lye enters the second-stage flash separation tower for gas-liquid separation; A third-stage circulating pump is arranged at the bottom of the third-stage flash separation tower, part of the waste lye is delivered to a third-stage heating chamber through the third-stage circulating pump for heating, the waste lye flow rate is 269.25-279.25 t / h, and after heating, the waste lye enters the third-stage flash separation tower for gas-liquid separation.

4. The process for COD removal from evaporated condensate of POSM spent caustic as claimed in claim 1 wherein, The temperature of the POSM waste lye is 43-45℃, the pressure is 1.20-1.40 MPaG, the pressure of the waste lye is reduced to 0.4 MPaG by the pressure-reducing valve, and the flow rate of the POSM waste lye is 272.7-282.7 t / h.

5. The process as claimed in claim 1, wherein the process is characterized by, The temperature of the secondary steam condensate in the first-stage flash separation tower is 70-76℃, the pressure is 500-540 KPaG, and the flow rate is 0.98-1.02 t / h; The temperature of the secondary steam condensate in the second-stage flash separation tower is 70-76℃, the pressure is 500-540 KPaG, and the flow rate is 1.08-1.18 t / h; The temperature of the secondary steam condensate in the third-stage flash separation tower is 70-80℃, the pressure is 500-560 KPaG, and the flow rate is 1.22-1.32 t / h.

6. The process as claimed in claim 1, wherein the process for removal of COD from evaporated condensate of POSM spent caustic comprises of: The flow rate of the waste lye in the rectification tower is 28.35-30.35 t / h.

7. The process as claimed in claim 1, wherein the process is characterized by, The waste liquid at the bottom of the stripping tower is cooled to 65-69℃ by a first-stage raw material preheater, and then cooled to 40-44℃ by a tower kettle cooler, with a pressure of 0.6-0.7 MPaG and a flow rate of 27.57-29.57 t / h.

8. The process as claimed in claim 1, wherein the process for removal of COD from evaporated condensate of POSM spent caustic solution is characterized by, The overhead gas of the stripping tower is cooled to 95-102℃ by a second-stage raw material preheater, and then cooled to 42-45℃ by an overhead liquid cooler of the stripping tower; The temperature of the overhead gas of the stripping tower is 126-130℃, the pressure is 0.15-0.17 MPaG, and the flow rate is 4-6 t / h.

9. The process as claimed in claim 1, wherein the process for removal of COD from evaporated condensate of POSM spent caustic solution is characterized by, Part of the water phase is delivered to the rectifying tower as overhead reflux liquid by a reflux pump, with a flow rate of 3.22-4.22 t / h, and the other part is discharged outside.

10. The process as claimed in claim 1, wherein the process for removal of COD from evaporated condensate of POSM spent caustic comprises of, The heat source of the first-stage raw material preheater is the tower kettle liquid of the rectifying tower, and the heat source of the second-stage raw material preheater is the overhead gas of the rectifying tower.

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