A method for efficiently recovering waste caustic water containing chloroethylene in synthesis of chloroethylene by calcium carbide method

Abstract

The application provides a high-efficiency recovery method for waste caustic water containing vinyl chloride in synthesis of vinyl chloride by calcium carbide method, belongs to the technical field of waste caustic water recovery, and solves the problem that waste caustic water cannot be recovered efficiently in the synthesis process of vinyl chloride. The device used in the application comprises a waste water tank, a waste water stripping tower, a vinyl chloride gas tank, a reboiler, a waste water cooler connected with the reboiler, a waste water neutralization tank, a primary sedimentation tank and a secondary sedimentation tank, a sludge tank, a clean water tank, two active carbon filters connected with the clean water tank respectively, an RO water inlet tank, a reverse osmosis device, an RO water outlet tank, a mixed bed and a circulating water tank. After the waste caustic water containing alkali is stripped, the qualified water is recycled by treatment of the waste caustic water by means of sedimentation, pressure filtration, active carbon filtration, reverse osmosis, a decarbonization tower and a mixed bed. The application realizes recovery and recycling of the waste caustic water containing vinyl chloride, realizes recycling of vinyl chloride, reduces production and operation cost, realizes zero discharge of waste water, and achieves good economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of waste alkaline water recycling technology, specifically relating to an efficient method for recycling vinyl chloride-containing waste alkaline water in the synthesis of vinyl chloride using the calcium carbide method. Background Technology

[0002] In the calcium carbide method for vinyl chloride production, hydrogen chloride reacts with acetylene to produce vinyl chloride. This process produces acidic byproducts, such as residual hydrogen chloride and carbon dioxide. Alkaline washing neutralizes these acidic substances with sodium hydroxide solution to ensure product purity. Alkaline washing of vinyl chloride is not only a purification process, but also a key step in ensuring continuous production, environmental protection, economic efficiency, and improving product quality and equipment lifespan.

[0003] Alkaline washing is a chemical absorption operation in which a chemical reaction occurs. Carbon dioxide and trace amounts of hydrogen chloride can be removed through alkaline washing. The equipment typically includes an alkaline washing tower, using a dilute sodium hydroxide solution as the chemical absorbent. A 10%-15% sodium hydroxide solution is used. Crude vinyl chloride gas is washed to neutral before being sent to subsequent production processes. When the alkaline solution concentration is <10% or sodium carbonate ≥5%, fresh alkaline solution needs to be replaced. Waste alkaline solution is usually discharged directly into the wastewater treatment process. Direct discharge presents the following problems:

[0004] 1. Chlorinated alkaline solutions contain high concentrations of sodium chloride, organic matter, and may also contain unreacted vinyl chloride monomers. Direct discharge into wastewater treatment plants will cause eutrophication of the wastewater treatment plant's water bodies, inhibit the growth of aquatic organisms, and affect the ecological balance of the water treatment process.

[0005] 2. Since vinyl chloride is a flammable and explosive gas, its discharge into the sewage treatment plant poses a risk of flash explosion, resulting in a significant safety hazard.

[0006] 3. In the production of polyvinyl chloride, vinyl chloride is a valuable raw material. The failure to recycle it results in serious waste. At the same time, the treatment and discharge of wastewater also leads to the waste of water resources. Summary of the Invention

[0007] The purpose of this invention is to provide an efficient method for recovering vinyl chloride-containing waste alkaline water in the synthesis of vinyl chloride via the calcium carbide process, so as to solve the problem of inefficient recovery of waste alkaline water in the process of vinyl chloride synthesis.

[0008] The technical solution of this invention is: a highly efficient method for recovering vinyl chloride-containing waste alkaline water in the synthesis of vinyl chloride by the calcium carbide method. The structure of the device used is as follows: a wastewater tank is connected to a wastewater stripping tower. The top of the wastewater stripping tower is connected to a vinyl chloride gas holder. The bottom of the wastewater stripping tower is connected to a reboiler. The reboiler is connected in sequence to a wastewater cooler, a wastewater neutralization tank, a primary sedimentation tank, and a secondary sedimentation tank. The bottoms of the primary and secondary sedimentation tanks are connected to a sludge tank. The secondary sedimentation tank is connected to a clear water tank. The clear water tank is connected to a first activated carbon filter and a second activated carbon filter. The bottoms of the first and second activated carbon filters are connected to an RO inlet tank. The RO inlet tank is connected in sequence to a reverse osmosis device, an RO permeate tank, multiple mixed beds, and a circulating water tank. The reverse osmosis device is also connected to the primary sedimentation tank.

[0009] The method includes the following steps:

[0010] Step 1: The alkaline wastewater in the wastewater tank is sent to the wastewater stripping tower for stripping. At the bottom of the wastewater stripping tower, the reboiler generates upward steam that comes into countercurrent contact with the wastewater, providing vaporization energy. The vinyl chloride in the wastewater is heated and vaporized into gas, which comes into contact with the wastewater, realizing full mass transfer between the gas and liquid phases and achieving the transfer of vinyl chloride into the gas phase. The vinyl chloride exiting from the top of the wastewater stripping tower is recovered and reused by the vinyl chloride gas holder.

[0011] Step 2: After stripping the wastewater in the wastewater stripping tower, the wastewater enters the wastewater neutralization tank for neutralization. The wastewater cooler indirectly cools the stripped wastewater through heat exchange. The supernatant of the neutralized wastewater is then treated by first-stage and second-stage sedimentation tanks before entering the clear water tank. The unsettled wastewater enters the sludge tank.

[0012] Step 3: The wastewater from the clear water tank is filtered through the first activated carbon filter and the second activated carbon filter. The filtered wastewater enters the RO feed tank in sequence and is then treated by the reverse osmosis unit, the RO permeate tank and multiple mixed beds. The qualified water is sent to the circulating water tank for recycling. The concentrated water after the reverse osmosis unit is sent to the primary sedimentation tank for further recycling.

[0013] As a further improvement of the present invention, a nitrogen pipeline, a hydrochloric acid pipeline and a vent pipe are respectively provided at the top of the wastewater neutralization tank, and the nitrogen pipeline leads to the bottom of the wastewater neutralization tank.

[0014] As a further improvement of the present invention, a clear water pump and a backwash pump are respectively connected to the bottom of the clear water tank. The output end of the clear water pump is connected to the top of the first activated carbon filter and the second activated carbon filter and is equipped with valve A. The input end of the RO water inlet tank is equipped with valve B. The output end of the backwash pump is connected to the bottom of the first activated carbon filter and the second activated carbon filter. The top of the first activated carbon filter and the second activated carbon filter is connected to the primary sedimentation tank and is equipped with valve C. The output end of the backwash pump is equipped with valve D.

[0015] During normal operation of the device, by opening valves A and B and closing valves C and D, the wastewater in the clear water tank is filtered through the first activated carbon filter and the second activated carbon filter; by opening valves C and D and closing valves A and B, the first activated carbon filter and the second activated carbon filter are backwashed, and the backwashed wastewater is sent to the primary sedimentation tank for further recycling and treatment.

[0016] As a further improvement of the present invention, a frame plate filter press is provided between the sludge tank and the clear water tank.

[0017] As a further improvement of the present invention, a security filter is connected between the RO inlet tank and the reverse osmosis device.

[0018] As a further improvement of the present invention, a decarbonization tower is provided on the RO permeate tank, and a blower is provided at the bottom of the decarbonization tower.

[0019] As a further improvement of the present invention, the bottom of the reboiler is connected to the wastewater tank via a condensate collection pipe.

[0020] The beneficial effects of this invention are as follows: This invention addresses the vinyl chloride-containing waste alkali generated during the production of polyvinyl chloride (PVC). By stripping the alkaline wastewater and neutralizing it with hydrochloric acid, a byproduct of the production process, and then treating it through sedimentation, pressure filtration, activated carbon filtration, reverse osmosis, decarbonization tower, and mixed bed processes, the treated water that meets the required standards is reused in the circulating water tank for replenishment and recycling. This achieves the recycling of vinyl chloride-containing waste alkali water and the recovery and recycling of vinyl chloride, reduces production and operating costs, achieves zero wastewater discharge, and yields good economic and social benefits.

[0021] By configuring valves on two activated carbon filters, switching between filtration and backwashing can be achieved. During normal operation, opening valves A and B and closing valves C and D allows wastewater from the clear water tank to be filtered through the activated carbon filters via a clear water pump. Opening valves C and D and closing valves A and B allows the activated carbon filters to be backwashed by a backwash pump. The backwash wastewater is then piped to a primary settling tank for further recycling. This process removes impurities from the fluid, improves its purity, removes impurities trapped in the filter layer, restores the filtration capacity of the equipment, and collectively ensures the efficient operation of the treatment system and the safety of the water quality. Attached Figure Description

[0022] Figure 1 This is a connection structure diagram of the device used in this invention.

[0023] In the diagram: 1-Wastewater tank; 2-Wastewater stripping pump; 3-Wastewater stripping tower; 4-vinyl chloride gas holder; 5-Wastewater cooler; 6-Reboiler; 7-Wastewater neutralization tank; 8-Settling pump; 9-Primary settling tank; 10-Secondary settling tank; 11-Sludge tank; 12-Sludge pump; 13-Frame plate filter press; 14-Clear water tank; 15-Clear water pump; 16-Backwash pump; 171-First activated carbon filter; 172-Second activated carbon filter; 18-RO inlet tank; 19-RO inlet pump; 20-Security filter; 21- Reverse osmosis unit; 22-RO permeate tank; 23-Decarbonization tower; 24-Blower; 25-Mixed bed feed pump; 26-Mixed bed; 27-Circulating water tank; 28-Vent pipe; 29-Coagulant pipe; 30-Circulating water supply pipe; 31-Circulating water return pipe; 32-Steam pipe; 33-Condensate collection pipe; 34-Waste alkaline water inlet pipe; 35-Flocculant pipe; 36-Hydrochloric acid pipe; 37-Nitrogen pipe; 38-Concentrate pipe; 39-Valve A; 40-Valve B; 41-Valve C; 42-Valve D. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] like Figure 1 As shown, a highly efficient method for recovering vinyl chloride-containing waste alkaline water from the synthesis of vinyl chloride using the calcium carbide method is described. The apparatus structure is as follows: a wastewater tank 1 is connected to a wastewater stripping tower 3. The top of the wastewater stripping tower 3 is connected to a vinyl chloride gas holder 4. The bottom of the wastewater stripping tower 3 is connected to a reboiler 6. The reboiler 6 is sequentially connected to a wastewater cooler 5, a wastewater neutralization tank 7, a primary sedimentation tank 9, and a secondary sedimentation tank 10. The bottoms of the primary sedimentation tank 9 and the secondary sedimentation tank 10 are connected to a sludge tank 11. The secondary sedimentation tank 10 is connected to a clear water tank 14. The clear water tank 14 is connected to a first activated carbon filter 171 and a second activated carbon filter 172. The bottoms of the first activated carbon filter 171 and the second activated carbon filter 172 are connected to an RO inlet tank 18. The RO inlet tank 18 is sequentially connected to a reverse osmosis unit 21, an RO product water tank 22, multiple mixed beds 26, and a circulating water tank 27. The reverse osmosis unit 21 is also connected to the primary sedimentation tank 9.

[0026] The method includes the following steps:

[0027] Step 1: The alkaline wastewater in wastewater tank 1 is sent to wastewater stripping tower 3 for stripping. At the bottom of wastewater stripping tower 3, steam is generated upward through reboiler 6 and comes into countercurrent contact with the wastewater, providing vaporization energy. The vinyl chloride in the wastewater is heated and vaporized into gas and comes into contact with the wastewater, realizing full gas-liquid phase mass transfer and achieving vinyl chloride gas phase transfer. The vinyl chloride exiting from the top of wastewater stripping tower 3 is recovered and reused by vinyl chloride gas holder 4.

[0028] Step 2: After stripping the wastewater in the wastewater stripping tower 3, the wastewater enters the wastewater neutralization tank 7 for neutralization. The wastewater cooler 5 indirectly cools the stripped wastewater through heat exchange. The supernatant of the neutralized wastewater passes through the primary sedimentation tank 9 and the secondary sedimentation tank 10 for sedimentation treatment before entering the clear water tank 14. The unsettled wastewater enters the sludge tank 11.

[0029] Step 3: The wastewater in the clear water tank 14 is filtered through the first activated carbon filter 171 and the second activated carbon filter 172. The filtered wastewater enters the RO inlet tank 18 in sequence and is treated by the reverse osmosis unit 21, the RO product water tank 22 and multiple mixed beds 26. The qualified water is sent to the circulating water tank 27 for recycling. The concentrated water after treatment by the reverse osmosis unit 21 is sent to the primary sedimentation tank 9 for further recycling.

[0030] The top of the wastewater neutralization tank 7 is equipped with a nitrogen pipe 37, a hydrochloric acid pipe 36, and a vent pipe 28, with the nitrogen pipe 37 leading to the bottom of the wastewater neutralization tank 7. The bottom of the clear water tank 14 is connected to a clear water pump 15 and a backwash pump 16, with the output end of the clear water pump 15 connected to the top of the first activated carbon filter 171 and the second activated carbon filter 172 and equipped with a valve A39. The input end of the RO inlet tank 18 is equipped with a valve B40. The output end of the backwash pump 16 is connected to the bottom of the first activated carbon filter 171 and the second activated carbon filter 172, with the top of the first activated carbon filter 171 and the second activated carbon filter 172 connected to the primary sedimentation tank 9 and equipped with a valve C41. The output end of the backwash pump 16 is equipped with a valve D42.

[0031] During normal operation of the device, by opening valves A39 and B40 and closing valves C41 and D42, the wastewater in the clear water tank 14 is filtered through the first activated carbon filter 171 and the second activated carbon filter 172. By opening valves C41 and D42 and closing valves A39 and B40, the first activated carbon filter 171 and the second activated carbon filter 172 are backwashed. The backwashed wastewater is sent to the primary sedimentation tank 9 for further recycling and treatment.

[0032] A frame plate filter press 13 is installed between the sludge tank 11 and the clear water tank 14; a security filter 20 is connected between the RO inlet tank 18 and the reverse osmosis unit 21; a decarbonization tower 23 is installed on the RO product water tank 22, and a blower 24 is installed at the bottom of the decarbonization tower 23; the bottom of the reboiler 6 is connected to the wastewater tank 1 through a condensate collection pipe 33.

[0033] Example 1

[0034] Wastewater tank 1 is equipped with a steel-lined PTFE storage tank. Since the incoming wastewater carries vinyl chloride, there is a safety risk. Therefore, a closed storage tank is required for temporary buffer storage of the wastewater. The design must comprehensively consider safety, operability, environmental protection, and durability to ensure stability during storage and reduce the risk of accidents.

[0035] Wastewater tank 1 is equipped with a waste alkali water inlet pipe 34 at the top, and a valve is installed on the waste alkali water inlet pipe 34 for control. The purpose of wastewater tank 1 is to ensure the continuous operation of the wastewater stripping unit and to temporarily store the waste alkali liquid from the vinyl chloride alkali washing tower. Wastewater tank 1 has an outlet pipe at the bottom that connects to wastewater stripping pump 2. Wastewater stripping pump 2 is connected to the inlet of wastewater stripping tower 3 via a pipe, delivering wastewater to wastewater stripping tower 3. Wastewater stripping tower 3 is designed as a stainless steel sieve plate tower. Wastewater tank 1, wastewater stripping pump 2, and inlet / outlet pipes are required to be made of stainless steel to avoid corrosion from the waste alkali liquid.

[0036] A reboiler 6 is connected to the bottom of the wastewater stripping tower 3. The reboiler 6 is a shell-and-tube heat exchanger. The inlet and outlet of the tube side are connected to the bottom of the wastewater stripping tower 3 through pipelines to form a loop connection. The shell side inlet of the reboiler 6 is designed with a steam pipe 32 to introduce steam for heating, and the shell side condensate outlet is designed with a condensate collection pipe 33. Wastewater is sent to the upper part of the tower by the wastewater stripping pump 2 and enters the wastewater stripping tower 3. Steam is introduced into the shell side of the bottom reboiler 6 for heating. The upward steam generated at the bottom of the wastewater stripping tower 3 comes into countercurrent contact with the wastewater, providing vaporization energy. The vinyl chloride in the wastewater is heated and vaporized into gas. The vinyl chloride gas phase comes into contact with the wastewater through the tower plates, realizing full gas-liquid mass transfer and achieving vinyl chloride gas phase transfer. The vinyl chloride exiting the top of the wastewater stripping tower 3 is transported through pipelines to the vinyl chloride gas holder 4 in the main process production unit for recycling.

[0037] The wastewater stripping tower 3 is designed to control parameters such as temperature, pressure, liquid level, and gas flow rate to ensure stripping efficiency, avoid overheating and overload, and guarantee continuous production. After passing through the wastewater stripping tower 3, vinyl chloride in the wastewater is effectively separated, achieving its recovery and reuse. The vinyl chloride gas holder 4 is a storage device in the vinyl chloride purification process, regulating the supply and demand imbalance between production and consumption, storing excess volume, ensuring continuous and stable production, and preventing production interruptions or excessive emissions.

[0038] Wastewater stripping tower 3 is equipped with a wastewater cooler 5 at the bottom. The wastewater cooler 5 is designed as a shell and tube heat exchanger. After the wastewater is stripped at the bottom of the wastewater stripping tower 3, it is controlled by the liquid level and enters the wastewater neutralization tank 7 through the top pipe of the wastewater neutralization tank 7 via the designed high level difference. The inlet of the shell side of the wastewater cooler 5 is cooled by circulating water through the circulating water supply pipe 30, and the outlet is cooled by the circulating water return pipe 31. The circulating water is sent to the circulating water system of the device for recycling. The wastewater cooler 5 is designed to indirectly cool the stripped wastewater by circulating water. The steam condensate from the reboiler 6 flows to the wastewater tank 1 through the condensate collection pipe 33. Since the steam condensate has a high temperature, it directly heats the wastewater in the wastewater tank 1, reducing the heat loss of the wastewater stripping tower 3 and realizing the recovery and utilization of heat.

[0039] Wastewater neutralization tank 7 is designed with a stainless steel pipe storage tank, specifically a steel-lined PTFE tank. Periodic spark testing of the lining is required to prevent corrosion and leakage. A nitrogen pipeline 37 runs from the top of wastewater neutralization tank 7 to its bottom, and a hydrochloric acid pipeline 36 is located at the top. The designed hydrochloric acid concentration is 18%-22%. Hydrochloric acid is added to wastewater neutralization tank 7, and nitrogen agitation is activated to ensure complete acid-base neutralization. Wastewater neutralization tank 7 requires an online pH monitoring and display device for timely adjustment of the hydrochloric acid dosage. To prevent pressure buildup during nitrogen purging and agitation, a vent pipe 28 is installed at the top of wastewater neutralization tank 7 to facilitate nitrogen release during agitation, thereby controlling the pH of the waste alkaline solution in wastewater neutralization tank 7 to remain stable between 7 and 9.

[0040] An outlet is installed at the bottom of the wastewater neutralization tank 7, which is connected to a sedimentation pump 8 via a pipeline. The outlet of the sedimentation pump 8 transports the neutralized wastewater from the wastewater neutralization tank 7 to the primary sedimentation tank 9 via a pipeline. The wastewater enters the bottom of the primary sedimentation tank 9 from one side and flows to the subsequent treatment process through the overflow outlet at the top of the other side. A coagulant is quantitatively added to the top of the primary sedimentation tank 9 through a coagulant pipeline 29. Through charge neutralization and compression of the double electric layer, the stability of suspended particles is destroyed, and the repulsive force between particles is weakened, preparing for the subsequent flocculation process. Most of the flocculants are mainly polyaluminum chloride. After being added to the water, they release polyvalent cations to neutralize the charge of the negatively charged suspended particles in the water, thereby reducing the electrostatic repulsion between particles and making it easier for suspended solids to aggregate and settle. As a result, the chloride salts in the wastewater are deposited at the bottom of the sedimentation tank and flow to the sludge tank 11 through a pipeline. The supernatant of the wastewater overflows to the secondary sedimentation tank 10 through the other side of the top of the primary sedimentation tank 9. The primary sedimentation tank 9, secondary sedimentation tank 10, sludge tank 11 and clear water tank 14 are designed with a height difference in sequence. The supernatant of wastewater can achieve gravity sedimentation flow through the height difference and flow through the primary sedimentation tank 9 and secondary sedimentation tank 10 in sequence to the clear water tank 14.

[0041] The primary sedimentation tank 9 and the secondary sedimentation tank 10 utilize gravity sedimentation to degrade organic matter by microorganisms, remove BOD, ammonia nitrogen and phosphorus, biodegrade and degrade pollutants, improve water quality, and at the same time settle suspended solids (chloride salts, silt, soil, biological solids and suspended organic matter) in wastewater to the bottom, while the supernatant overflows and removes suspended solids.

[0042] The secondary settling tank 10 operates on the same principle as the primary settling tank 9. A flocculant pipe 35 is installed at the top of the secondary settling tank 10 to quantitatively add flocculant, further promoting and optimizing the growth and aggregation of the initially formed flocs, making them more stable, larger, and easier to settle. Polyacrylamide is typically used as the flocculant. The settled suspended solids are discharged to the sludge tank 11 through a bottom pipe, while the supernatant overflows to the clear water tank 14 through the other side of the top of the secondary settling tank 10. The design volumes of the primary settling tank 9 and the secondary settling tank 10 must meet the settling requirements, and the dosages of coagulant and flocculant must be calculated based on production needs.

[0043] The bottom of the sludge tank 11 is connected to the sludge pump 12 via a pipeline. The sludge is then transported to the frame plate filter press 13 for filtration. After filtration, the sludge is dried and collected in a collection tank and then processed as mercury-containing sludge. The clear liquid from the frame plate filter press 13 is then transported to the clear water tank 14 for further processing.

[0044] An outlet pipe is installed at the bottom of the clear water tank 14, which is connected to the clear water pump 15 and the backwash pump 16 via a T-junction. Wastewater from the clear water tank 14 is transported to two activated carbon filters for filtration via a pipe installed at the outlet of the clear water pump 15. The wastewater filtered by the first activated carbon filter 171 and the second activated carbon filter 172 enters the RO inlet tank 18 for temporary storage. Two activated carbon filters are installed in parallel and filled with activated carbon. The activated carbon filters effectively adsorb residual chlorides in the water, such as sodium chloride, protecting the subsequent reverse osmosis unit 21, extending its lifespan, and reducing disinfection byproducts.

[0045] The first activated carbon filter 171 and the second activated carbon filter 172 can switch between filtration and backwashing operations via valves. During normal operation, by opening valves A39 and B40 and closing valves C41 and D42, wastewater from the clear water tank 14 is filtered through the activated carbon filters by the clear water pump 15. Since the vinyl chloride-containing waste alkaline water is intermittently transported, the activated carbon filters can be backwashed when the upstream system stops transporting the wastewater. This is done by opening valves C41 and D42 and closing valves A39 and B40, using the backwash pump 16 to backwash the activated carbon filters. The backwash wastewater is then transported through pipelines to the primary settling tank 9 for further recycling. The activated carbon filters can be operated intermittently according to production schedules, or backwashing can be performed using inlet and outlet pressure gauges to reference the pressure difference.

[0046] Wastewater filtered by the first activated carbon filter 171 and the second activated carbon filter 172 enters the RO inlet tank 18. The RO inlet tank 18 is required to be made of stainless steel, and its design, including its volume, must match the capacity of the subsequent reverse osmosis unit 21. An outlet is provided at the bottom of the RO inlet tank 18, which is connected to the RO inlet pump 19 via a pipe. The RO inlet pump 19 is connected to the security filter 20 via a pipe. The main function of the security filter 20 is to remove fine particles (0.1-5 microns), protect the RO membrane from scratches, extend the service life of the RO membrane, remove particles and colloids from the water, improve the clarity of the inlet water, ensure efficient RO permeation, reduce membrane fouling, increase water production, and improve the quality of the effluent.

[0047] The outlet pipe of the security filter 20 is connected to the inlet of the reverse osmosis unit 21. The reverse osmosis unit 21 mainly utilizes a semi-permeable membrane with selective permeability, allowing water molecules to pass through while blocking large molecules, ions, organic matter, bacteria, viruses, etc., efficiently separating water from impurities. After the wastewater from the outlet of the security filter 20 is treated by the reverse osmosis unit 21, the concentrate outlet of the reverse osmosis unit 21 is transported to the primary sedimentation tank 9 through the concentrate pipe 38 for further recycling. The permeate from the reverse osmosis unit 21 is transported to the RO permeate tank 22 through a pipeline. A decarbonation tower 23 is installed at the top of the RO permeate tank 22, and a blower 24 is installed at the bottom of the decarbonation tower 23. The permeate from the reverse osmosis unit 21 flows through the top of the decarbonation tower 23 and sprays into the RO permeate tank 22. During operation, the blower 24 provides counter-current airflow to the decarbonation tower 23 to remove carbon dioxide from the RO permeate, reducing the production load of the subsequent mixed bed unit 26. The purpose of setting up the decarbonation tower 23 is because carbon dioxide reacts with water to form carbonic acid, which lowers the pH value of the influent, affects the resin exchange capacity, and reduces efficiency.

[0048] An outlet is located at the bottom of the RO permeate tank 22, connected to a mixed bed feed pump 25 via a pipe. The pump delivers the RO permeate to two mixed beds 26 for treatment. Each mixed bed 26 requires a separate acid / alkali regeneration device. Anion and cation exchange resins are added to the mixed bed 26. The cation exchange resin attracts and removes cations (such as sodium, calcium, and magnesium), while the anion exchange resin adsorbs anions (such as chloride and sulfate). As water passes through the mixed bed 26, the cation and anion exchange resins intermingle, and the reactions occur almost simultaneously, rapidly removing ions from the water. Simultaneously, H₂O is generated. + OH - Immediate bonding minimizes the formation of counterions, reducing their impact and ensuring thorough exchange for excellent water quality. Ion exchange occurs through the anion and cation exchange resins in the mixed bed 26, further removing calcium and magnesium ions from the RO permeate. This ensures the treated wastewater conductivity is ≤10 US / cm². Wastewater passing through the mixed bed 26 and meeting testing standards is then sent to the circulating water tank 27 for makeup water reuse.

[0049] By using the above method and the equipment, the efficient recovery of vinyl chloride-containing waste alkaline water in the synthesis of vinyl chloride by the calcium carbide method can be achieved, realizing the recycling of vinyl chloride and achieving zero discharge of wastewater. The equipment used in this method is a device for recovering flammable and explosive media. Its design and installation must meet the requirements for chemical fire prevention and explosion protection. The device must be purged with nitrogen before operation.

Claims

1. A highly efficient method for recovering vinyl chloride-containing alkaline wastewater from the synthesis of vinyl chloride via the calcium carbide process, characterized in that: The structure of the device used is as follows: it includes a wastewater tank (1), which is connected to a wastewater stripping tower (3). The top of the wastewater stripping tower (3) is connected to a vinyl chloride gas holder (4). The bottom of the wastewater stripping tower (3) is connected to a reboiler (6). The reboiler (6) is connected in sequence to a wastewater cooler (5), a wastewater neutralization tank (7), a primary sedimentation tank (9), and a secondary sedimentation tank (10). The bottoms of the primary sedimentation tank (9) and the secondary sedimentation tank (10) are connected to a sludge tank (11). The secondary sedimentation tank (11) is connected to a sludge tank (11). 0) Connected to a clear water tank (14), the clear water tank (14) is connected to a first activated carbon filter (171) and a second activated carbon filter (172) respectively. The bottom of the first activated carbon filter (171) and the second activated carbon filter (172) are connected to an RO inlet tank (18). The RO inlet tank (18) is connected in sequence to a reverse osmosis device (21), an RO product water tank (22), multiple mixed beds (26) and a circulating water tank (27). The reverse osmosis device (21) is also connected to a primary sedimentation tank (9). The method includes the following steps: Step 1: The alkaline wastewater in the wastewater tank (1) is sent to the wastewater stripping tower (3) for stripping. The bottom of the wastewater stripping tower (3) generates upward steam through the reboiler (6) and comes into countercurrent contact with the wastewater to provide vaporization energy. The vinyl chloride in the wastewater is heated and vaporized into gas and comes into contact with the wastewater to achieve full gas-liquid phase mass transfer and realize the transfer of vinyl chloride gas phase. The vinyl chloride exiting the top of the wastewater stripping tower (3) is recycled by the vinyl chloride gas holder (4). Step 2: Wastewater stripping tower (3) After stripping, the wastewater enters the wastewater neutralization tank (7) for neutralization. The wastewater cooler (5) performs indirect heat exchange cooling on the stripped wastewater. The supernatant of the neutralized wastewater passes through the primary sedimentation tank (9) and the secondary sedimentation tank (10) for sedimentation treatment and then enters the clear water tank (14). The unsettled wastewater enters the sludge tank (11). Step 3: The wastewater in the clear water tank (14) is filtered through the first activated carbon filter (171) and the second activated carbon filter (172). The filtered wastewater enters the RO inlet tank (18) in sequence and is treated by the reverse osmosis device (21), the RO permeate tank (22) and multiple mixed beds (26). The qualified water is sent to the circulating water tank (27) for recycling. The concentrated water after treatment by the reverse osmosis device (21) is sent to the primary sedimentation tank (9) for further recycling.

2. The efficient method for recovering vinyl chloride-containing alkaline wastewater from the calcium carbide-based vinyl chloride synthesis according to claim 1, characterized in that: The top of the wastewater neutralization tank (7) is equipped with a nitrogen pipe (37), a hydrochloric acid pipe (36) and a vent pipe (28), and the nitrogen pipe (37) leads to the bottom of the wastewater neutralization tank (7).

3. A highly efficient method for recovering vinyl chloride-containing waste alkaline water from the synthesis of vinyl chloride via the calcium carbide process, as described in claim 1 or 2, characterized in that: The bottom of the clear water tank (14) is connected to a clear water pump (15) and a backwash pump (16). The output end of the clear water pump (15) is connected to the top of the first activated carbon filter (171) and the second activated carbon filter (172) and is equipped with valve A (39). The input end of the RO inlet tank (18) is equipped with valve B (40). The output end of the backwash pump (16) is connected to the bottom of the first activated carbon filter (171) and the second activated carbon filter (172). The top of the first activated carbon filter (171) and the second activated carbon filter (172) is connected to the first-stage sedimentation tank (9) and is equipped with valve C (41). The output end of the backwash pump (16) is equipped with valve D (42). During normal operation of the device, by opening valves A (39) and B (40) and closing valves C (41) and D (42), the wastewater in the clear water tank (14) is filtered through the first activated carbon filter (171) and the second activated carbon filter (172); by opening valves C (41) and D (42) and closing valves A (39) and B (40), the first activated carbon filter (171) and the second activated carbon filter (172) are backwashed, and the backwashed wastewater is sent to the primary sedimentation tank (9) for further recycling.

4. The efficient recovery method for vinyl chloride-containing waste alkaline water in the synthesis of vinyl chloride via the calcium carbide process according to claim 3, characterized in that: A frame plate filter press (13) is provided between the sludge tank (11) and the clear water tank (14).

5. The efficient method for recovering vinyl chloride-containing waste alkaline water in the synthesis of vinyl chloride via the calcium carbide process according to claim 4, characterized in that: A security filter (20) is connected between the RO inlet tank (18) and the reverse osmosis device (21).

6. The efficient method for recovering vinyl chloride-containing waste alkaline water in the synthesis of vinyl chloride via the calcium carbide process according to claim 5, characterized in that: The RO permeate tank (22) is equipped with a decarbonization tower (23), and a blower (24) is installed at the bottom of the decarbonization tower (23).

7. The efficient method for recovering vinyl chloride-containing waste alkaline water in the synthesis of vinyl chloride via the calcium carbide process according to claim 1, characterized in that: The bottom of the reboiler (6) is connected to the wastewater tank (1) via a condensate collection pipe (33).

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