POSM waste lye concentration process and device

Abstract

This invention relates to a POSM waste alkali solution concentration process and apparatus. The process is a "triple-effect forced circulation evaporation + stripping" process. First, the waste alkali solution is concentrated through countercurrent multi-effect evaporation. The evaporated condensate is then stripped to further reduce COD. The apparatus includes a triple-effect evaporator, a second-effect evaporator, a first-effect evaporator, and a stripping tower. The evaporation separation chamber is equipped with separation packing and a condenser. The stripping utilizes pressurized distillation, and the corresponding reflux tank has phase separation capabilities, enabling the separation of the organic and aqueous phases. A heat exchanger is installed to thermally couple the stripping tower's top vapor phase with the evaporation concentrate feed, reducing energy consumption. This invention can effectively reduce the COD value of the evaporated condensate and improve the waste alkali solution concentration ratio.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, specifically a concentration process and apparatus for POSM waste alkaline solution. Background Technology

[0002] Industrially, propylene oxide (PO) is often produced via a co-oxidation process, simultaneously generating styrene (SM). However, POSM (Polystyrene-to-Oxygen) plants produce large quantities of POSM wastewater during operation. Due to its high pH, ​​this wastewater is also known as alkali waste. POSM alkali wastewater also exhibits high COD and is difficult to biodegrade, making it challenging to treat using conventional biological processes. Currently, the main methods for treating POSM alkali wastewater both domestically and internationally include incineration, wet oxidation pretreatment followed by biological post-treatment, and supercritical water oxidation. Incineration is widely used due to its mature technology and short process flow. However, incineration consumes large amounts of fuel, and the high water content, organic matter, and salt content in the wastewater result in excessively high operating costs. Therefore, the concentration of alkali wastewater has become a research hotspot.

[0003] Chinese patent CN107512751A employs an evaporation method to convert cyclohexanone saponification waste alkali liquid into a gaseous phase, followed by defoaming and separation. The gaseous phase is then compressed by a compressor and used as a heat source for evaporation. The condensate enters a water treatment system, resulting in concentrated waste alkali liquid. This concentration method utilizes MVR technology, which is relatively energy-efficient, but the equipment investment is high. The enrichment of organic matter in the gaseous phase reduces the heat exchange temperature difference, leading to low concentration of the waste alkali liquid. Simple evaporation results in a high COD value in the condensate, making water treatment difficult and costly.

[0004] Chinese patent CN111437617B describes a continuous steam stripping process for waste alkaline solution from cyclohexane oxidation, yielding a gas phase containing effective components and the stripped waste alkaline solution. The advantages are the recovery of effective components such as cyclohexane, cyclohexanone, and cyclohexanol from the waste alkaline solution through stripping, a simple process, and a relatively short flow rate. The disadvantages are a higher content of other light and heavy components in the gas phase at the top of the tower, a high water content in the stripped waste alkaline solution, and greater difficulty in incineration.

[0005] Therefore, simply evaporating and concentrating or stripping waste alkaline solution cannot simultaneously control the COD in the condensate and significantly reduce the amount to be incinerated, thus having limitations. This invention improves multi-effect evaporation and stripping technologies and couples them with energy-saving techniques to achieve both concentration of waste alkaline solution and reduction of COD in the condensate. Summary of the Invention

[0006] The purpose of this invention is to address the problems of high COD value in POSM waste alkali condensate, high wastewater treatment costs, and low concentration ratio of waste alkali condensate, by providing a POSM waste alkali condensate concentration process and apparatus. This process is a "triple-effect forced circulation evaporation + stripping" process. First, the waste alkali condensate is concentrated through countercurrent multi-effect evaporation. The condensate is then stripped to further reduce COD. In the apparatus, the evaporation separation chamber is equipped with separation packing and a condenser. The stripping uses pressurized distillation, which is beneficial for the enrichment of organic matter at the top of the column (azeotropic). The corresponding reflux tank has phase separation capabilities, enabling the separation of the organic and aqueous phases. A heat exchanger is installed to thermally couple the top gas phase with the evaporation feed, reducing energy consumption. This invention can effectively reduce the COD value of the condensate, increase the concentration ratio of waste alkali condensate, and is less likely to clog pipes and incineration nozzles.

[0007] The technical problem solved by this invention is achieved through the following technical solution:

[0008] A POSM waste alkali solution concentration process includes the following steps:

[0009] Waste alkali solution is sent by raw material feed pump P1 to the primary raw material preheater E1 and the secondary raw material preheater E2 for preheating, and then enters the triple-effect evaporator T1 for forced circulation evaporation. The reflux liquid obtained by the rectification section and the fractionating condenser in the separation chamber is returned to the tower. The secondary gas is condensed by the primary indirect condenser CX1, and the condensate obtained enters the stripping liquid inlet tank V1. The non-condensable gas enters the secondary indirect condenser CX2 for condensation to obtain concentrated organic light components. The remaining non-condensable gas is deeply cooled by the tertiary indirect condenser CX3 (-15℃~-10℃). The condensate from the secondary indirect condenser CX2 and the tertiary indirect condenser CX3 enters the organic liquid tank V5. The organic liquid wastewater is pumped to the concentrated alkali solution storage tank V4 by the organic liquid pump. The non-condensable gas is pumped to the tail gas treatment system by the vacuum pump.

[0010] The triple-effect evaporator T1 operates at a pressure of 70-90 kPa, with a condenser reflux ratio of 0.05-0.3, a vapor exit temperature of 89.5℃-96.3℃, and a bottom temperature of 91.1℃-97.9℃. The preferred operating pressure is 80 kPa and the reflux ratio is 0.1.

[0011] The temperature range of the waste alkali solution flowing out of the primary raw material preheater E1 is 79.6℃-82.8℃; the temperature range of the waste alkali solution flowing out of the secondary raw material preheater E2 is 125.1℃-127.7℃.

[0012] After triple-effect concentration, the alkali solution is sent to the second-effect feed preheater E4 via triple-effect discharge pump P2. After heat exchange with stripping steam (the material outlet temperature range of the second-effect feed preheater E4 is 120.9℃-127.6℃), it enters the second-effect evaporator T2. The alkali solution from the triple-effect concentration undergoes forced circulation evaporation in the second-effect heater E4. The condensate containing heavy components obtained by passing through the rectification section in the separation chamber and part of the evaporated condensate is returned to the tower. Secondary gas (104.8℃-111.4℃) enters the shell side of the triple-effect heating chamber E3 as a heat source, and the condensate enters the condensate tank V2. The concentrated alkali solution is sent to the first-effect evaporator T3 via second-effect discharge pump P3.

[0013] The operating pressure of the double-effect evaporator T2 is 120-150 kPa, the reflux ratio is 0.1-0.5, the gas phase exit temperature is 104.8℃-111.4℃, the bottom temperature is 106.5℃-113.1℃, and the preferred operating pressure is 135 kPa with a reflux ratio of 0.15.

[0014] The alkali solution from the second-effect concentration is sent to the first-effect evaporator T3 via the second-effect discharge pump P3. After being heated by the first-effect heater E6 (124.1℃-130℃), it undergoes forced circulation evaporation. The condensate containing heavy components obtained by passing through the rectification section in the separation chamber and part of the evaporated condensate is returned to the tower. The secondary gas separated from the first-effect separation chamber enters the second-effect heating chamber E5 (106.5℃-113.1℃) as the heat source for evaporation. The concentrated alkali solution flows by gravity to the concentrated alkali solution storage tank V4 via the liquid level difference, and is then sent to the incinerator for incineration via the concentrated alkali solution discharge pump P10.

[0015] The single-effect evaporator T3 operates at a pressure of 200-240 kPa, a reflux ratio of 0.15-0.5, a vapor exit temperature of 120.2℃-126.1℃, and a bottom temperature of 124.1℃-130℃. The preferred operating pressure is 200 kPa and the reflux ratio is 0.2.

[0016] After heat exchange, the condensate from the first-effect evaporator and the second-effect evaporator flows by gravity to the condensate tank V2. A small amount of condensate in the condensate tank V2 is sent by the condensate pump P8 to the rectification sections of the first-effect evaporator T3 and the second-effect evaporator T2 as reflux liquid to control the entrainment and volatilization of heavy organic components. The remaining condensate, together with the first-stage condensate from the third-effect evaporator, is sent to the stripping inlet tank V1 of the stripping section for further removal of organic components.

[0017] The condensate from the stripping feed tank V1 is sent to the upper part of the stripping tower T4 by the stripping feed pump P4. Under pressurized operation, the organic components are stripped away. The gas phase at the top of the tower is condensed by thermal coupling with the evaporation section and then enters the reflux tank V3 (the gas phase at the top of the tower exchanges heat with the second-effect feed preheater E4 and the secondary feed preheater E2 in the evaporation section, and the liquid phase returns to the stripping section reflux tank after heat exchange). In the reflux tank V3, it is divided into an aqueous phase and an organic phase. The aqueous phase is sent to the top of the stripping tower for reflux by the reflux pump P5. The organic phase is condensed by the top condensate recooler CX5 and then sent to the concentrated alkali storage tank V4. After that, it is sent to the incinerator for incineration by the concentrated alkali pump P10. The qualified bottom liquid is sent to the primary feed preheater E1 in the evaporation section for preheating of the feed and the recooler CX6 for cooling before going to the biochemical treatment.

[0018] Since the stripping tower operates under pressure, the gas phase temperature is high and the calorific value is large. Therefore, a thermal coupling method is used to exchange heat between the stripping tower gas phase and the secondary feed preheater and the double-effect feed preheater. This reduces the use of condensate water and the amount of steam required to heat the raw materials, thus saving energy significantly.

[0019] The stripping tower T4 operates at a pressure of 280-320 kPa, a reflux ratio of 3-3.6, a vapor exit temperature of 112.8℃-117.7℃, and a bottom temperature of 131.6℃-136.1℃. The preferred operating pressure is 300 kPa and the reflux ratio is 3.4. The cooling temperatures of the top condensate recoolers CX5 and CX6 are below 40℃.

[0020] The three condensers CX1, CX2, and CX3 connected to the triple-effect evaporator T1 receive gas from the triple-effect evaporator T1 containing water and some organic matter. The COD content in the condensate is controlled by adjusting the gas phase fraction using the first-stage indirect condenser CX1. After condensation by CX1, the condensate mainly contains water, and the remaining non-condensable gases are mainly organic matter with low boiling points. After condensation by CX2 and CX3, the condensate enters the organic liquid tank V5. The gas phase fraction of the first-stage indirect condenser CX1 is 0.03-0.05.

[0021] The three evaporation separation chambers are equipped with a rectification section, and the triple-effect evaporator is equipped with a condenser to control the entrainment and volatilization of organic heavy components.

[0022] The process flow described is a "triple-effect evaporation + stripping" process, where evaporation is performed first followed by stripping. Because the evaporation tower contains a rectification section, the entrainment and volatilization of heavy components can be effectively controlled during the evaporation process, resulting in an organic component content of less than 0.1% in the final vapor condensate. In contrast, the "stripping + triple-effect evaporation" process involves stripping first and then evaporation. During stripping, it is impossible to control the entrainment of heavy components, resulting in a high content of heavy components in the vapor at the top of the tower. The organic component content in the final vapor condensate is only less than 0.5%. Therefore, the triple-effect evaporation + stripping process, with its rectification section in the evaporation tower, achieves a more ideal concentration effect.

[0023] The composition of the POSM waste alkaline solution by mass percentage includes 87%-92% water, 3%-5% organic salts (sodium phenolate, sodium benzoate, sodium formate, sodium propionate), 2%-4% propylene glycol, 2%-3% other organic impurities, and 0.9%-1.2% sodium hydroxide.

[0024] Another technical solution of the present invention to solve the technical problem is as follows:

[0025] A POSM waste alkali solution concentration and treatment device, the device includes a triple-effect evaporator T1, a double-effect evaporator T2, a single-effect evaporator T3 and a stripping tower T4;

[0026] The raw material feed pump P1 is connected to the primary raw material preheater E1 and the secondary raw material preheater E2, and then to the separation chamber of the triple-effect evaporator T1 via pipeline 1. The top outlet of the triple-effect evaporator T1 is sequentially connected to the primary indirect condenser CX1, the secondary indirect condenser CX2, and the tertiary indirect condenser CX3. The lower part of the triple-effect evaporator T1 is connected to the inlet of the forced circulation pump P11 via pipeline. The outlet of P11 is connected to the triple-effect heater E3 via pipeline and then to the triple-effect separation chamber. The bottom outlet of the tower is sequentially connected to the triple-effect discharge pump P2 and the secondary feed preheater E4, and then enters the separation chamber of the secondary-effect evaporator T2 via pipeline 2. The primary indirect condenser CX1 enters the stripping liquid inlet tank V1 via pipeline 3. The secondary indirect condenser CX2 and the tertiary indirect condenser CX3 are respectively connected to the organic liquid tank V5, and the tertiary indirect condenser CX3 is connected to the tail gas treatment system. The organic liquid tank V5 is connected to the organic liquid pump P9 and then enters the concentrated alkali liquid tank V4.

[0027] The top outlet of the second-effect evaporator T2 is connected to the shell side of the third-effect heater E3, and then to the condensate tank V2 via pipe 4; the lower part of the second-effect evaporator T2 is connected to the inlet of the forced circulation pump P12 via pipe, and the outlet of P12 is connected to the second-effect heater E5 via pipe, and then to the second-effect separation chamber; the bottom outlet of the tower is connected to the second-effect discharge pump P3, and then to the separation chamber of the first-effect evaporator T3 via pipe 5.

[0028] The top outlet of the first-effect evaporator T3 is connected to the shell side of the second-effect heater E5, and then to the condensate tank V2 via pipe 4; the lower part is connected to the inlet of the forced circulation pump P13 via pipe, and the outlet of P13 is connected to the first-effect heater E6 via pipe, and then to the first-effect separation chamber; the bottom outlet of the tower is connected to the concentrated alkali tank V4 via pipe 6; one outlet of the condensate tank V2 is connected to the top reflux port of the second-effect evaporator T2 and the first-effect evaporator T3 via the secondary condensate reflux pump P8, and the other outlet is connected to the stripping feed tank V1 via pipe 3; the stripping feed tank V1 is connected to the stripping tower T4 via the stripping feed pump P4.

[0029] One outlet of the stripping tower T4 is connected to the start-up condenser CX4, and the other is connected to the shell side of the second-effect feed preheater E4 and the shell side of the secondary feed preheater, and then connected to the reflux tank V3 via pipe 7. The outlet of the reflux tank V3 is connected to the top reflux pump P5 and then to the top of the stripping tower T4. The other outlet is connected to the concentrated alkali tank V4 via the top condensate recooler CX5 and the condensate discharge pump P6. The bottom outlet is connected to the stripping tower reboiler E7 and then to the bottom of the stripping tower. The other outlet is connected to the stripping bottom liquid discharge pump P7 and then connected to the condensate recooler CX6 via the shell side of the primary feed preheater E1, and then sent to the biochemical treatment system.

[0030] The triple-effect evaporator T1 comprises, from bottom to top, a gas-liquid separation chamber, a rectification section, and a condenser. The rectification section is neatly equipped with... filler The theoretical number of plates is 8-12. The condenser is connected to the rectification section via a flange, and the condensate is directly refluxed to the packing layer of the rectification section. The feed inlet is located in the middle of the separation chamber.

[0031] The double-effect evaporator T2 includes a gas-liquid separation chamber and a rectification section. The rectification section is equipped with structured packing material, with a theoretical plate count of 10-14. A liquid distributor is installed above the packing layer, and the reflux port is located above the distributor. The feed inlet is located in the middle of the separation chamber.

[0032] The single-effect evaporator T3 includes a gas-liquid separation chamber and a rectification section. The rectification section is equipped with structured packing with 10-16 theoretical plates. A liquid distributor is installed above the packing layer, and the reflux port is located above the distributor. The feed inlet is located in the middle of the separation chamber.

[0033] The T4 stripping tower is a packed tower filled with structured packing. The theoretical number of plates is 35-45, the feed plate number is 7-12, and the reflux port is located at the top of the reflux distributor.

[0034] The triple-effect evaporator T1, the double-effect evaporator T2, and the single-effect evaporator T3 contain a rectification section and a condenser reflux section.

[0035] The outlet of the raw material feed pump P1 is equipped with a flow meter;

[0036] The outlet of the organic liquid tank V5 is equipped with a liquid level regulating valve;

[0037] The triple-effect discharge pump P2, the double-effect discharge pump P3, and the single-effect discharge pipeline are equipped with liquid level regulating valves.

[0038] The beneficial effects of this invention are as follows:

[0039] In the current industrial incineration process for treating waste alkali, the large volume and high water content of the waste alkali lead to excessively high incineration costs. Furthermore, the composition and content of impurities in the waste alkali produced by different processes vary. During simple evaporation or stripping, the gas phase at the top of the tower contains not only light components but also components that azeotropically react with water. At the same time, some heavy components are carried out with the gas phase at the top of the tower, resulting in excessively high COD of the gas phase at the top of the tower, reaching 160,000-200,000 mg / L. This leads to excessively high water treatment costs. Moreover, the high content of heavy components can easily cause pipe blockage and corrosion after cooling due to solidification and accumulation in the pipeline.

[0040] This invention is scientifically and rationally designed, employing a "triple-effect forced circulation evaporation + stripping" technology. Evaporation is performed first, followed by stripping. Each evaporation effect includes a rectification section to effectively control the volatile entrainment of heavy components. The triple-effect evaporation uses three-stage indirect condensation to adjust the gas phase fraction, effectively separating condensate from non-condensable organic gases and reducing the COD value of the aqueous phase. The triple-effect forced circulation evaporation involves re-distilling the concentrate from the previous effect after each evaporation, utilizing the added rectification section in the separation chamber and the reflux liquid from the fractionating condenser to control the entrainment of heavy components. Since POSM waste alkaline solution contains a significant amount of benzene impurities, most of which azeotropically react with water and are collected with the water, pressurization is used in the stripping section to increase the content of these impurities in the azeotropic composition, reducing the water content and thus lowering the energy consumption of incineration. The concentrate is collected from the first effect; its high temperature and low viscosity prevent clogging of pipes and incineration nozzles.

[0041] When simply evaporating and concentrating, the COD value of the condensate can be as high as 20,000-50,000 mg / L. The process of this invention can effectively reduce the COD value of the waste liquid to 1,000-5,000 mg / L, reduce the volume of concentrated waste alkali liquid by 30%, and reduce incineration fuel consumption by 30%. This invention also adopts thermal coupling technology, where the gas phase at the top of the stripping tower exchanges heat with the raw material, thereby reducing the steam consumption in the evaporation process. Based on the calculation of processing 30 tons of waste alkali liquid per hour, it saves 3-3.8 t / h of steam and 180 t / h of circulating water consumption in the stripping tower. Attached Figure Description

[0042] Figure 1 This is a diagram of a POSM waste alkali concentration device;

[0043] In the diagram, T1: triple-effect evaporator; T2: double-effect evaporator; T3: single-effect evaporator; T4: stripping tower.

[0044] E1: Primary feed preheater; E2: Secondary feed preheater; E3: Triple-effect heater; E4: Secondary feed preheater; E5: Secondary feed preheater; E6: Primary heater; E7: Stripper reboiler; CX1: Primary indirect condenser; CX2: Secondary indirect condenser; CX3: Tertiary indirect condenser; CX4: Start-up condenser; CX5: Top condensate recooler; CX6: Recooler; P1: Feed pump; P2: Triple-effect outlet pump. Feed pump; P3: Second-effect discharge pump; P4: Stripping feed pump; P5: Tower top reflux pump; P6: Condensate discharge pump; P7: Stripping kettle liquid discharge pump; P8: Secondary condensate reflux pump; P9: Organic liquid pump; P10: Concentrated alkali discharge pump; P11: Triple-effect circulation pump; P12: Second-effect circulation pump; P13: First-effect circulation pump; V1: Stripping feed tank; V2: Condensate tank; V3: Reflux tank; V4: Concentrated alkali tank; V5: Organic liquid tank; Detailed Implementation

[0045] The following is in conjunction with the appendix Figure 1 The invention is further illustrated by examples. However, the following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the invention.

[0046] like Figure 1 As shown, the POSM waste alkali solution concentration treatment device of the present invention includes a triple-effect evaporator T1, a double-effect evaporator T2, a single-effect evaporator T3, and a stripping tower T4.

[0047] The raw material feed pump P1 is connected to the primary raw material preheater E1 and the secondary raw material preheater E2, and then to the separation chamber of the triple-effect evaporator T1 via pipeline 1. The top outlet of the triple-effect evaporator T1 is sequentially connected to the primary indirect condenser CX1, the secondary indirect condenser CX2, and the tertiary indirect condenser CX3. The lower part of the triple-effect evaporator T1 is connected to the inlet of the forced circulation pump P11 via pipeline. The outlet of P11 is connected to the triple-effect heater E3 via pipeline, and then to the triple-effect separation chamber (forced circulation heating and evaporation of materials). The bottom outlet of the tower is sequentially connected to the triple-effect discharge pump P2 and the secondary feed preheater E4, and then enters the separation chamber of the secondary-effect evaporator T2 via pipeline 2. The primary indirect condenser CX1 enters the stripping liquid inlet tank V1 via pipeline 3. The secondary indirect condenser CX2 and the tertiary indirect condenser CX3 are respectively connected to the organic liquid tank V5, and the tertiary indirect condenser CX3 is connected to the tail gas treatment system. The organic liquid tank V5 is connected to the organic liquid pump P9 and then enters the concentrated alkali liquid tank V4.

[0048] The top outlet of the second-effect evaporator T2 is connected to the shell side of the third-effect heater E3, and then to the condensate tank V2 via pipe 4; the lower part of the second-effect evaporator T2 is connected to the inlet of the forced circulation pump P12 via pipe, and the outlet of P12 is connected to the second-effect heater E5 via pipe, and then to the second-effect separation chamber; the bottom outlet of the tower is connected to the second-effect discharge pump P3, and then to the separation chamber of the first-effect evaporator T3 via pipe 5.

[0049] The top outlet of the first-effect evaporator T3 is connected to the shell side of the second-effect heater E5, and then to the condensate tank V2 via pipe 4; the lower part is connected to the inlet of the forced circulation pump P13 via pipe, and the outlet of P13 is connected to the first-effect heater E6 via pipe, and then to the first-effect separation chamber; the bottom outlet of the tower is connected to the concentrated alkali tank V4 via pipe 6; one outlet of the condensate tank V2 is connected to the top reflux port of the second-effect evaporator T2 and the first-effect evaporator T3 via the secondary condensate reflux pump P8, and the other outlet is connected to the stripping feed tank V1 via pipe 3; the stripping feed tank V1 is connected to the stripping tower T4 via the stripping feed pump P4.

[0050] One outlet of the stripping tower T4 is connected to the start-up condenser CX4, and the other is connected to the shell side of the second-effect feed preheater E4 and the shell side of the secondary feed preheater, and then connected to the reflux tank V3 via pipe 7. The outlet of the reflux tank V3 is connected to the top reflux pump P5 and then to the top of the stripping tower T4. The other outlet is connected to the concentrated alkali tank V4 via the top condensate recooler CX5 and the condensate discharge pump P6. The bottom outlet is connected to the stripping tower reboiler E7 and then back to the bottom of the stripping tower. The other outlet is connected to the stripping bottom liquid discharge pump P7 and then connected to the condensate recooler CX6 via the shell side of the primary feed preheater E1, and then sent to the biochemical treatment system.

[0051] The triple-effect evaporator T1 comprises, from bottom to top, a gas-liquid separation chamber, a rectification section, and a condenser. The rectification section is equipped with structured packing material, with a theoretical plate count of 8-12. The condenser is connected to the rectification section via a flange, and the condensate is directly returned to the packing layer in the rectification section. The feed inlet is located in the middle of the separation chamber.

[0052] The double-effect evaporator T2 includes a gas-liquid separation chamber and a rectification section. The rectification section is equipped with structured packing material, with a theoretical plate count of 10-14. A liquid distributor is installed above the packing layer, and the reflux port is located above the distributor. The feed inlet is located in the middle of the separation chamber.

[0053] The single-effect evaporator T3 includes a gas-liquid separation chamber and a rectification section. The rectification section is equipped with structured packing with 10-16 theoretical plates. A liquid distributor is installed above the packing layer, and the reflux port is located above the distributor. The feed inlet is located in the middle of the separation chamber.

[0054] The T4 stripping tower is a packed tower filled with structured packing. The theoretical number of plates is 35-45, the feed plate number is 7-12, and the reflux port is located at the top of the reflux distributor.

[0055] The triple-effect evaporator T1, the double-effect evaporator T2, and the single-effect evaporator T3 contain a rectification section and a condenser reflux section.

[0056] The outlet of the raw material feed pump P1 is equipped with a flow meter;

[0057] The outlet of the organic liquid tank V5 is equipped with a liquid level regulating valve;

[0058] The triple-effect discharge pump P2, the double-effect discharge pump P3, and the single-effect discharge pipeline are equipped with liquid level regulating valves.

[0059] In the aforementioned triple-effect evaporator T1, the separation chamber is Φ2800×5000mm and the rectification section is DN1000×6000mm, filled with 5m² 250Y structured packing, and the condenser is 40m². 2 DN800×1500mm;

[0060] In the double-effect evaporator T2, the separation chamber is Φ2400×4500mm and the rectification section is DN900×6000mm, filled with 5m250Y structured packing.

[0061] In the single-effect evaporator T3, the separation chamber is Φ2200×4500mm and the rectification section is DN900×6000mm, filled with 5m250Y structured packing.

[0062] In stripping tower T4, Φ1000×26000mm is filled with 3m 500Y structured packing and 15m 250Y structured packing.

[0063] In the aforementioned process:

[0064] Waste alkali solution is sent by raw material feed pump P1 to the primary raw material preheater E1 and the secondary raw material preheater E2 for preheating, and then enters the triple-effect evaporator T1 for forced circulation evaporation. The entrainment and volatilization of organic heavy components are controlled by the rectification section and the condenser in the separation chamber of the tower. The secondary gas is condensed by the primary indirect condenser CX1 and then enters the condensate tank V2. The non-condensable gas, which is the concentrated organic light component, enters the secondary indirect condenser CX2 for condensation. The remaining non-condensable gas is deeply cooled by the tertiary indirect condenser CX3. The condensate from the secondary indirect condenser CX2 and the tertiary indirect condenser CX3 enters the organic liquid tank V5. The organic liquid wastewater is pumped to the concentrated alkali solution storage tank V4 by the organic liquid pump. The non-condensable gas is pumped to the tail gas treatment system by the vacuum pump.

[0065] After triple-effect concentration, the alkali solution is sent to the second-effect feed preheater E4 via triple-effect discharge pump P2, where it exchanges heat with stripping steam before entering the second-effect evaporator T2. The alkali solution from the triple-effect concentration undergoes forced circulation evaporation in the second-effect heating chamber. The entrainment and volatilization of heavy organic components are controlled by the rectification section in the separation chamber and the reflux of part of the evaporated condensate. Secondary gas enters the shell side of the triple-effect heating chamber E3 as a heat source. The concentrated alkali solution is sent to the first-effect evaporator T3 via second-effect discharge pump P3.

[0066] The alkali solution from the second-effect concentration is sent to the first-effect evaporator T3 via the second-effect discharge pump P3. After being heated in the first-effect heating chamber E6, it is forced to circulate and evaporate. The entrainment and volatilization of organic heavy components are controlled by the rectification section in the separation chamber and the reflux of part of the evaporated condensate. The secondary gas separated from the first-effect separation chamber enters the second-effect heating chamber E5 as the heat source for evaporation. The concentrated alkali solution flows by gravity to the concentrated alkali solution storage tank V4 via the liquid level difference, and is sent to the incinerator for incineration via the concentrated alkali solution discharge pump P10.

[0067] The condensate from the first and second effects of evaporation enters the stripping feed tank V1. Part of it is pumped back to the rectification section of the first-effect evaporator T3 and the second-effect evaporator T2 to control the entrainment and volatilization of heavy organic components. The remainder is sent to the stripping feed tank V1 in the stripping section for the removal of organic components and further extraction of organic matter.

[0068] Using the secondary gas condensate from the evaporation section and the condensate from the primary indirect condenser as raw materials, the condensate from the stripping feed tank V1 is sent to the upper part of the stripping tower T4 by the stripping feed pump P4. Under high pressure, organic components are stripped away. The gas phase at the top of the tower is condensed by thermal coupling with the evaporation section and then enters the reflux tank V3 (the gas phase at the top of the tower exchanges heat with the secondary feed preheater E2 in the evaporation section; after heat exchange, the liquid phase returns to the stripping section reflux tank). In the reflux tank V3, it separates into an aqueous phase and an organic phase. The aqueous phase is sent to the top of the distillation tower for reflux by the reflux pump P5, while the organic phase is condensed by the top condensate recooler CX5 and then sent to the concentrated alkali storage tank V4. From there, it is sent to the incinerator for incineration by the concentrated alkali pump P10. The qualified bottom liquid is sent to the primary feed preheater E1 in the evaporation section for preheating and to the recooler CX6 for cooling before being sent to the biochemical treatment plant.

[0069] Example 1

[0070] The following description is based on the example of processing 30.08 tons of POSM waste alkaline solution per hour.

[0071] The composition of the POSM waste alkaline solution by mass percentage includes 90% water, 3.5% organic salts (sodium phenolate, sodium benzoate, sodium formate, sodium propionate), 3% propylene glycol, 2.5% other organic impurities, and 1% sodium hydroxide.

[0072] A POSM waste alkali concentration process is described. The POSM waste liquid from the reaction zone has a temperature of 25℃. After being preheated (126.5℃) by the primary feed preheater E1 and the secondary feed preheater E2, it enters the triple-effect evaporator T1 for forced circulation evaporation. The feed rate is 30.08 t / h. The triple-effect evaporator T1 has 10 theoretical plates, a feed position of 9, an operating pressure of 80 kPa, a vapor exit temperature of 93.1℃, a bottom temperature of 94.7℃, and a reflux ratio of 0.1. The vapor phase is condensed by the primary indirect condenser CX1 and then enters the condensate tank V2 at a flow rate of 7.16 t / h. Non-condensable gas... The concentrated organic light components are condensed in the secondary indirect condenser CX2. The remaining (2.6%) non-condensable gas is cryogenically cooled (to -12℃) in the tertiary indirect condenser CX3. The condensate (organic liquid wastewater) from the secondary and tertiary indirect condensers CX2 and CX3 enters the organic liquid tank V5 (components: water, propylene oxide, benzaldehyde, propylene glycol) at a flow rate of 0.429 t / h. The organic liquid wastewater (water, propylene oxide, benzaldehyde, propylene glycol) is sent to the concentrated alkali storage tank V4 via the organic liquid pump P9. The non-condensable gas (propylene oxide) is sent to the tail gas treatment system by a vacuum pump at a flow rate of 0.001 t / h.

[0073] The alkali solution, after being concentrated in the triple-effect reactor, is sent to the second-effect feed preheater E4 via the triple-effect discharge pump P2. After heat exchange with stripping steam, it enters the second-effect evaporator T2. The feed rate is 22.49 t / h, the feed temperature is 124.5℃, the theoretical plate number of the second-effect evaporator T2 is 10, the feed position is 9, the operating pressure is 135 kPa, the vapor exit temperature is 108.2℃, the bottom temperature is 110℃, and the reflux ratio is 0.15. The alkali solution from the triple-effect reactor undergoes intense heating in the second-effect heating chamber. The system operates in a circulating evaporation process. The entrainment and volatilization of heavy organic components are controlled by the rectification section in the separation chamber and the reflux of part of the evaporated condensate. At this point, the water content in the gas phase is 99.6%, and the gas flow rate is 6.65 t / h. The concentrated alkaline solution (85.9% water, 5.8% propylene glycol, 0.4% phenylethanol, and the remainder being organic salts (sodium phenolate, sodium benzoate, sodium formate, sodium propionate) and organic impurities) is sent to the first-effect evaporation tower T3 via the second-effect discharge pump P3 at a flow rate of 15.84 t / h.

[0074] The alkali solution from the second-effect concentration is sent to the first-effect evaporator T3 via the second-effect discharge pump P3. The feed temperature is 110.3℃, the feed rate is 15.84t / h, the theoretical plate number of the first-effect evaporator T3 is 10, the feed position is 9, the operating pressure is 220Kpa, the vapor exit temperature is 123.3℃, ​​the vapor flow rate is 7.26t / h, the bottom temperature is 127.2℃, and the reflux ratio is 0.2. The alkali solution from the second-effect concentration passes through the first-effect heating chamber E6. After heating, the mixture is forced to evaporate. The entrainment and volatilization of heavy organic components are controlled by the rectification section on the separation chamber and the reflux of part of the evaporated condensate. The concentrated alkali solution (composed of: water 74%, propylene glycol 10.6%, phenylethanol 0.8%, the remaining organic salts (sodium phenolate, sodium benzoate, sodium formate, sodium propionate) and organic impurities) flows by gravity to the concentrated alkali solution storage tank V4 via the liquid level difference, with a flow rate of 8.58 t / h. It is then sent to the incinerator for incineration by the concentrated alkali solution discharge pump P10.

[0075] The secondary gas condensate from the evaporation section and the condensate from the first-stage indirect condenser are used as raw materials (composition: 98.9% water, 0.2% propylene oxide, 0.5% benzaldehyde, 0.1% acetophenone, with the remainder being organic salts and organic impurities). The condensate from the stripping feed tank V1 is sent to the upper part of the stripping tower T4 by the stripping feed pump P4. The feed temperature is 106.1℃, the feed rate is 21.08 t / h, the theoretical plate number of the stripping tower T4 is 40, the feed position is 10, and the operating pressure is 3. The pressure is 00 kPa, the vapor exit temperature is 115.3℃, the column bottom temperature is 133.9℃, and the reflux ratio is 3.4. The feedstock undergoes stripping under high pressure to remove organic components. The vapor phase at the top of the column is condensed via thermal coupling with the evaporation section and then enters the reflux tank V3. It is then pumped by reflux pump P5 to the top portion of the distillation column for reflux. The remainder, treated as organic wastewater, is condensed by the column top condensate recooler CX5 and sent to the concentrated alkali storage tank V4 at a flow rate of 1 t / h. It is then pumped by concentrated alkali pump P10 to the incinerator for incineration. The qualified column bottom liquid (water content 99.9%) is pumped by discharge pump P7 to the primary feed preheater E1 of the evaporation section for preheating and cooled by recooler CX6 before being sent to the biochemical treatment plant at a flow rate of 20.08 t / h.

[0076] The above example uses a triple-effect forced circulation evaporation + stripping process to concentrate POSM waste alkaline liquid. The water content in the condensate from the second-effect evaporation and the first-effect evaporation reaches over 99.6%, and the water content in the stripped condensate also reaches over 99.9%. The water content of the waste liquid sent for incineration is reduced to below 75%, and the flow rate is reduced to 10 t / h. The water flow rate in the incineration waste liquid is reduced by 5-7.5 t / h, reducing the water gasification cost by 1000 yuan / h, which greatly reduces the cost of incineration treatment.

[0077] Example 2

[0078] The other steps are the same as in Example 1, except that the feed rate is changed from 30 t / h to 33 t / h, the reflux ratio of the triple-effect evaporator T1 is changed from 0.1 to 0.3, the operating pressure is changed from 80 kPa to 90 kPa, the gas phase temperature is changed from 93.1℃ to 96.3℃, and the reboiler temperature is changed from 94.7℃ to 97.9℃; the reflux ratio of the double-effect evaporator T2 is changed from 0.15 to 0.5, the operating pressure is changed from 135 kPa to 150 kPa, the gas phase temperature is changed from 108.2℃ to 111.4℃, and the reboiler temperature is changed from 110℃ to 113.1℃; and the reflux ratio of the single-effect evaporator T3 is changed from 0.2 to 0.5. The operating pressure changed from 220 kPa to 240 kPa, the gas phase temperature changed from 123.3℃ to 126.1℃, and the bottom temperature changed from 127.2℃ to 130℃. The reflux ratio of the stripping tower T4 changed from 3.4 to 3.6, the operating pressure changed from 300 kPa to 320 kPa, the gas phase temperature changed from 115.3℃ to 117.7℃, and the bottom temperature changed from 133.9℃ to 136.1℃. The water content in the condensate from the second-effect evaporation and the condensate from the first-effect evaporation reached more than 99.6%, the water content in the bottom liquid after stripping also reached more than 99.9%, and the water content in the waste liquid from the biochemical treatment was reduced to below 75%.

[0079] Comparative Example 1

[0080] Similarly, to process 30 tons of POSM waste alkali solution per hour, a stripping + triple-effect circulating evaporator is used (excluding the rectification section; the upper part of the feed inlet of the rectification column is called the rectification section, and the lower part is called the stripping section. That is, the upper part of the feed inlet of the three separation chambers is not filled with separation packing, and it only has the function of simple gas-liquid separation, without the function of controlling organic heavy components). The pressure inside the column is adjusted, and the concentrated product is obtained under normal operation.

[0081] The water content in the evaporation condensate of Comparative Example 1 was 99.4%, which was lower than the water content of 99.9% in the stripped condensate of Example 1. The heavy components were higher than those in Example 1. In addition, the water content of the concentrate in Comparative Example 1 was 87%, and the flow rate was 17.5 t / h, while that in Example 1 was below 75%, and the flow rate was 10 t / h. The water content in Example 1 was significantly reduced and the processing capacity was low. Example 1 can significantly reduce the cost of incineration treatment.

[0082] Matters not covered in this invention are common knowledge.

Claims

1. A POSM waste alkali solution concentration process, characterized in that, The process includes the following steps: Waste alkali solution is pumped by the raw material feed pump to the primary raw material preheater and the secondary raw material preheater for preheating, and then enters the triple-effect evaporator for forced circulation evaporation. The reflux liquid obtained through the rectification section and the fractionator in the separation chamber is returned to the tower. The secondary gas is condensed in the first-stage indirect condenser, and the resulting condensate enters the stripping liquid tank. The non-condensable gas is condensed in the second-stage indirect condenser to obtain concentrated organic light components. The remaining non-condensable gas is deeply cooled in the third-stage indirect condenser. The condensate from the second-stage and third-stage indirect condensers enters the organic liquid tank. The organic liquid wastewater is pumped to the concentrated alkali solution storage tank by the organic liquid pump. The non-condensable gas is pumped to the tail gas treatment system by the vacuum pump. The temperature of the third-stage indirect condenser is -15℃ to -10℃. The triple-effect evaporator operates at a pressure of 70-90 kPa, has a condenser reflux ratio of 0.05-0.3, a vapor exit temperature of 89.5℃-96.3℃, and a bottom temperature of 91.1℃-97.9℃. After triple-effect concentration, the alkali solution is pumped from the triple-effect outlet to the second-effect feed preheater, where it exchanges heat with stripping steam before entering the second-effect evaporator. The alkali solution from the triple-effect concentration undergoes forced circulation evaporation in the second-effect heater. The condensate containing heavy components, obtained from the rectification section in the separation chamber and part of the evaporated condensate, is returned to the tower. Secondary gas enters the shell side of the triple-effect heating chamber as a heat source, and the condensate enters the condensate tank. The concentrated alkali solution is pumped from the second-effect outlet to the first-effect evaporator. The material outlet temperature range of the second-effect feed preheater is 120.9℃-127.6℃; the temperature of the secondary gas is 104.8℃-111.4℃. The operating pressure of the double-effect evaporator is 120-150 kPa, the reflux ratio is 0.1-0.5, the gas phase exit temperature is 104.8℃-111.4℃, and the bottom temperature is 106.5℃-113.1℃. The alkali solution from the second-effect concentration is pumped to the first-effect evaporator via the second-effect discharge pump. After being heated by the first-effect heater, it undergoes forced circulation evaporation. The condensate containing heavy components, obtained from the rectification section in the separation chamber and part of the evaporated condensate, is returned to the tower. Secondary gas separated in the first-effect separation chamber enters the second-effect heating chamber as a heat source for evaporation. The concentrated alkali solution flows by gravity to the concentrated alkali solution storage tank via the liquid level difference, and is then pumped to the incinerator for incineration. The temperature of the first-effect heater is 124.1℃-130℃; the temperature of the second-effect heating chamber is 106.5℃-113.1℃. The single-effect evaporator operates at a pressure of 200-240 kPa, a reflux ratio of 0.15-0.5, a vapor exit temperature of 120.2℃-126.1℃, and a bottom temperature of 124.1℃-130℃. The condensate from the stripping feed tank is pumped to the upper part of the stripping tower by the stripping feed pump. Under pressurized operation, it is stripped to remove organic components. The vapor phase at the top of the tower is condensed by thermal coupling with the evaporation section and then enters the reflux tank. In the reflux tank, it is separated into an aqueous phase and an organic phase. The aqueous phase is pumped to the top of the stripping tower for reflux by the reflux pump. The organic phase is condensed by the condensate recooler at the top of the tower and then sent to the concentrated alkali storage tank. After that, it is pumped to the incinerator for incineration. The qualified bottom liquid is pumped to the primary feed preheater of the evaporation section for preheating the feed and the recooler for cooling before it is sent to the biochemical treatment. The stripping tower operates at a pressure of 280-320 kPa, a reflux ratio of 3-3.6, a vapor phase exit temperature of 112.8℃-117.7℃, and a bottom temperature of 131.6℃-136.1℃.

2. The POSM waste alkali concentration process as described in claim 1, characterized in that, The composition of the POSM waste alkaline solution by mass percentage includes 87%-92% water, 3%-5% organic salts, 2%-4% propylene glycol, 2%-3% other organic impurities, and 0.9%-1.2% sodium hydroxide; the organic salts are sodium phenolate, sodium benzoate, sodium formate, or sodium propionate.

3. The POSM waste alkali concentration process as described in claim 1, characterized in that, The triple-effect evaporator operates at a pressure of 80 kPa and a reflux ratio of 0.

1. The operating pressure in the double-effect evaporator is 135 kPa, and the reflux ratio is 0.

15. In the single-effect evaporator, the operating pressure is 200 kPa and the reflux ratio is 0.2; The stripping tower operates at a pressure of 300 kPa and a reflux ratio of 3.

4.

4. The POSM waste alkali concentration process as described in claim 1, characterized in that, The temperature range of the waste alkali solution flowing out of the primary raw material preheater is 79.6℃-82.8℃; the temperature range of the waste alkali solution flowing out of the secondary raw material preheater is 125.1℃-127.7℃.

5. A POSM waste alkali solution concentration and treatment device, characterized in that, The device includes a triple-effect evaporator, a double-effect evaporator, a single-effect evaporator, and a stripping tower; The raw material feed pump is connected to the primary and secondary raw material preheaters, and then to the separation chamber of the triple-effect evaporator via pipelines. The top outlet of the triple-effect evaporator is sequentially connected to the primary, secondary, and tertiary indirect condensers. The lower part of the triple-effect evaporator is connected to the inlet of a forced circulation pump via pipelines. The outlet of the forced circulation pump is connected to the triple-effect heater via pipelines, and then to the triple-effect separation chamber. The bottom outlet of the evaporator is sequentially connected to the triple-effect discharge pump and the secondary feed preheater, and then enters the separation chamber of the secondary evaporator via pipelines. The primary indirect condenser CX1 enters the stripping liquid inlet tank via pipelines. The secondary and tertiary indirect condensers are respectively connected to the organic liquid tank, while the tertiary indirect condenser is connected to the tail gas treatment system. The organic liquid tank is connected to the organic liquid pump and then enters the concentrated alkali liquid tank. The top outlet of the second-effect evaporator is connected to the shell side of the third-effect heater and then to the condensate tank via a pipeline; the lower part of the second-effect evaporator is connected to the inlet of the forced circulation pump via a pipeline, and the outlet of the forced circulation pump is connected to the second-effect heater via a pipeline and then to the second-effect separation chamber; the bottom outlet of the tower is connected to the second-effect discharge pump and then to the separation chamber of the first-effect evaporator via a pipeline. The top outlet of the first-effect evaporator is connected to the shell side of the second-effect heater and then to the condensate tank via a pipeline; the lower part is connected to the inlet of the forced circulation pump via a pipeline, and the outlet of the forced circulation pump is connected to the first-effect heater and then to the first-effect separation chamber via a pipeline; the bottom outlet of the tower is connected to the concentrated alkali tank via a pipeline; one outlet of the condensate tank is connected to the top reflux outlet of the second-effect evaporator and the first-effect evaporator via a secondary condensate reflux pump, and the other outlet is connected to the stripping feed tank via a pipeline; the stripping feed tank is connected to the stripping tower via the stripping feed pump. One outlet of the stripping tower is connected to the start-up condenser, and the other is connected to the shell side of the second-effect feed preheater and the shell side of the second-stage feed preheater, and then connected to the reflux tank via a pipeline, which is connected to the start-up condenser and the reflux tank. One outlet of the reflux tank is connected to the top reflux pump and then to the top of the stripping tower, and the other is connected to the concentrated alkali solution tank via the top condensate recooler and the condensate discharge pump. One outlet of the tower bottom is connected to the stripping tower reboiler and then back to the stripping tower bottom, and the other is connected to the stripping bottom liquid discharge pump, which is connected to the condensate recooler via the shell side of the first-stage feed preheater and then sent to the biochemical treatment system. The triple-effect evaporator comprises, from bottom to top, a gas-liquid separation chamber, a rectification section, and a condenser. The rectification section is filled with packing material, with a theoretical number of 8-12 plates. The condenser is connected to the rectification section via a flange, and the condensate flows directly back to the packing layer in the rectification section. The feed inlet is located in the middle of the separation chamber. The double-effect evaporator includes a gas-liquid separation chamber and a rectification section. The rectification section is equipped with structured packing with a theoretical plate number of 10-14. A liquid distributor is installed on the top of the packing layer, and the reflux port is located above the distributor. The feed inlet is located in the middle of the separation chamber. A single-effect evaporator includes a gas-liquid separation chamber and a rectification section. The rectification section is equipped with structured packing with a theoretical plate number of 10-16. A liquid distributor is installed on the top of the packing layer, and the reflux port is located above the distributor. The feed inlet is located in the middle of the separation chamber. The stripping tower is a packed tower filled with structured packing material. The theoretical number of plates is 35-45, the feed plate number is 7-12, and the reflux port is located at the top of the reflux distributor.

6. The POSM waste alkali solution concentration and treatment device as described in claim 5, characterized in that, The triple-effect evaporator, double-effect evaporator, and single-effect evaporator contain a rectification section and a condenser reflux section. The raw material feed pump outlet is equipped with a flow meter; The outlet of the organic liquid tank is equipped with a liquid level regulating valve; The triple-effect discharge pump, the double-effect discharge pump, and the single-effect discharge pipeline are equipped with liquid level regulating valves.

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