Efficient recovery method for vinyl chloride-containing waste alkaline water in calcium carbide method vinyl chloride synthesis

Abstract

The invention provides an efficient recovery method of waste alkaline water containing vinyl chloride in synthesis of vinyl chloride through a calcium carbide method, belongs to the technical field of waste alkaline water recovery, and solves the problem that waste alkaline water cannot be efficiently recovered in the synthesis process of vinyl chloride. The reboiler is connected with a wastewater cooler, a wastewater neutralizing tank, a primary sedimentation tank, a secondary sedimentation tank, a sludge tank and a clean water tank, and the clean water tank is respectively connected with two activated carbon filters, an RO (Reverse Osmosis) water inlet tank, a reverse osmosis device, an RO water producing tank, a mixed bed and a circulating water tank; after alkali liquor-containing wastewater is subjected to steam stripping, qualified water is recycled after being treated by devices such as sedimentation, filter pressing, activated carbon filtration, reverse osmosis, a decarburization tower and a mixed bed. According to the method, the recycling of the waste alkaline water containing the vinyl chloride is realized, meanwhile, the recycling of the vinyl chloride is realized, the production operation cost is reduced, the zero discharge of the wastewater is realized, and good economic benefits and social benefits are obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of waste alkaline water recovery, and specifically relates to a method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide process. Background Art

[0002] In the production process of vinyl chloride by the calcium carbide method, hydrogen chloride is reacted with acetylene to produce vinyl chloride. This process will produce acidic by-products, such as residual hydrogen chloride, carbon dioxide and other acidic media. 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 link to ensure production continuity, environmental protection, economic benefits, and improve product quality and equipment life.

[0003] Alkali washing is a chemical absorption operation. Chemical reactions occur during the absorption process. Carbon dioxide and trace amounts of hydrogen chloride can be removed through alkali washing. An alkali washing tower is usually set up in the device. A dilute solution of sodium hydroxide is used as a chemical absorbent. A sodium hydroxide solution with a concentration of 10%-15% is used. The crude vinyl chloride gas is washed to neutrality and then sent to subsequent production. When the alkali solution concentration is detected to be less than 10% or sodium carbonate is ≥5%, fresh alkali solution needs to be replaced. Usually, the waste alkali solution needs to be discharged directly to the sewage treatment process. Direct discharge has the following problems: 1. Vinyl chloride-containing alkali liquor contains high concentrations of sodium chloride, organic matter, and possibly unreacted vinyl chloride monomer, etc. Direct discharge to the sewage treatment plant will cause eutrophication of the sewage treatment plant water body, inhibit the growth of aquatic organisms, and affect the ecological balance of the water treatment process; 2. Since vinyl chloride is a flammable and explosive gas, there is a risk of flash explosion when it is discharged into a sewage treatment plant, which poses a high safety risk; 3. In the production of polyvinyl chloride, vinyl chloride is a precious raw material. If it is not recycled, it will cause serious waste. At the same time, the treatment and discharge of wastewater will cause a waste of water resources. Summary of the invention

[0004] The purpose of the present invention is to provide a method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide process, so as to solve the problem that the waste alkaline water cannot be efficiently recovered in the process of vinyl chloride synthesis.

[0005] The technical scheme of the present invention is: a method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide process, wherein the device structure used is as follows: comprising a wastewater tank, the 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 sequentially connected to a wastewater cooler, a wastewater neutralization tank, a primary sedimentation tank and a secondary sedimentation tank, the bottoms of the primary sedimentation tank and the secondary sedimentation tank are commonly connected to a sludge tank, the secondary sedimentation tank is connected to a clear water tank, the clear water tank is respectively connected to a first activated carbon filter and a second activated carbon filter, the bottoms of the first activated carbon filter and the second activated carbon filter are commonly connected to an RO water inlet tank, the RO water inlet tank is sequentially connected to a reverse osmosis device, an RO water production tank, a plurality of mixed beds and a circulating water tank, and the reverse osmosis device is also connected to the primary sedimentation tank; The method comprises the following steps: Step 1: send the alkali-containing wastewater in the wastewater tank to the wastewater stripping tower for gas stripping. The bottom of the wastewater stripping tower generates upward steam through a reboiler to contact the wastewater in countercurrent to provide vaporization energy. The vinyl chloride in the wastewater is heated and vaporized into gas to contact the wastewater, achieving sufficient gas-liquid mass transfer and vinyl chloride gas phase transfer. The vinyl chloride discharged from the top of the wastewater stripping tower is recycled by the vinyl chloride gas holder; Step 2: After the wastewater is stripped by the wastewater stripping tower, it enters the wastewater neutralization tank for neutralization. The wastewater cooler performs indirect heat exchange cooling on the stripped wastewater. The neutralized wastewater supernatant passes through the primary sedimentation tank and the secondary sedimentation tank in turn for sedimentation treatment and then enters the clear water tank. The unsettled wastewater enters the sludge tank. Step 3: The wastewater in the clear water tank is filtered through the first activated carbon filter and the second activated carbon filter. The filtered wastewater enters the RO water inlet tank in turn and passes through the reverse osmosis device, RO water production tank and multiple mixed beds for treatment. The water with qualified indicators is sent to the circulating water tank for recycling. The concentrated water treated by the reverse osmosis device is sent to the primary sedimentation tank for further recycling.

[0006] As a further improvement of the present invention, a nitrogen pipeline, a hydrochloric acid pipeline and a vent pipe are respectively provided on the top of the wastewater neutralization tank, and the nitrogen pipeline leads to the bottom of the wastewater neutralization tank.

[0007] As a further improvement of the present invention, a clean water pump and a backwash pump are respectively connected to the bottom of the clean water tank, the output end of the clean water pump is connected to the top of the first activated carbon filter and the second activated carbon filter and is provided with a valve A, and a valve B is provided on the input end of the RO water inlet tank; 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 provided with a valve C, and a valve D is provided on the output end of the backwash pump; During the normal operation of the device, by opening valve A and valve B, and closing valve C and valve D, the wastewater in the clean water tank is filtered through the first activated carbon filter and the second activated carbon filter; by opening valve C and valve D, and closing valve A and valve B, the first activated carbon filter and the second activated carbon filter are backwashed, and the wastewater after backwashing is sent to the primary sedimentation tank for further recovery and treatment.

[0008] As a further improvement of the present invention, a frame filter press is provided between the sludge tank and the clean water tank.

[0009] As a further improvement of the present invention, a safety filter is connected between the RO water inlet tank and the reverse osmosis device.

[0010] As a further improvement of the present invention, a decarbonization tower is provided on the RO water production tank, and a blower is provided at the bottom of the decarbonization tower.

[0011] As a further improvement of the present invention, the bottom of the reboiler is connected to the waste water tank through a condensed water collection pipe.

[0012] The beneficial effects of the present invention are as follows: the present invention aims at producing waste alkali containing vinyl chloride in the process of producing polyvinyl chloride, by stripping the alkali-containing wastewater, and neutralizing it with the by-product hydrochloric acid produced, and then after treatment by sedimentation, filter pressing, activated carbon filtration, reverse osmosis, decarbonization tower, mixed bed and the like, the treated water with qualified indicators is reused in the circulating water pool for water replenishment and recycling, thereby realizing the recycling of waste alkali water containing vinyl chloride and the recycling of vinyl chloride, reducing the production and operation costs, achieving zero discharge of wastewater, and achieving good economic and social benefits.

[0013] The switching operation between filtering and backwashing can be realized by setting valves on the two activated carbon filters to work together. During normal operation, valves A and B are opened, valves C and D are closed, and the wastewater in the clean water tank is filtered through the activated carbon filter by the clean water pump; valves C and D are opened, valves A and B are closed, and the activated carbon filter is backwashed by the backwash pump. The backwashing wastewater of the activated carbon filter is transported to the primary sedimentation tank through a pipeline for further recycling and treatment. In this way, impurities in the fluid are removed, the purity of the fluid is improved, impurities trapped in the filter layer are removed, and the filtering capacity of the filtering equipment is restored, which jointly ensures the efficient operation of the treatment system and the safety of water quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a structural diagram of the device connection used in the present invention.

[0015] In the figure: 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-sedimentation pump; 9-primary sedimentation tank; 10-secondary sedimentation tank; 11-sludge tank; 12-sludge pump; 13-frame 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 water inlet tank; 19-RO water inlet pump; 20-security filter; 21- Reverse osmosis device; 22-RO water production tank; 23-decarbonization tower; 24-blower; 25-mixed bed inlet pump; 26-mixed bed; 27-circulating water pool; 28-vent pipe; 29-coagulant pipeline; 30-circulating water supply pipe; 31-circulating water return pipe; 32-steam pipeline; 33-condensate collection pipeline; 34-waste alkali water inlet pipeline; 35-flocculant pipeline; 36-hydrochloric acid pipeline; 37-nitrogen pipeline; 38-concentrated water pipeline; 39-valve A; 40-valve B; 41-valve C; 42-valve D. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0017] like Figure 1 As shown, a method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide process, the device structure used is as follows, including a wastewater tank 1, the 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 primary sedimentation tank 9 and the secondary sedimentation tank 10 are commonly connected to a sludge tank 11 at the bottom, the secondary sedimentation tank 10 is connected to a clear water tank 14, the clear water tank 14 is respectively 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 commonly connected to an RO water inlet tank 18, the RO water inlet tank 18 is sequentially connected to a reverse osmosis device 21, an RO water production tank 22, a plurality of mixed beds 26 and a circulating water tank 27, and the reverse osmosis device 21 is also connected to the primary sedimentation tank 9; The method comprises the following steps: Step 1: sending the alkali-containing wastewater in the wastewater tank 1 to the wastewater stripping tower 3 for gas stripping. The bottom of the wastewater stripping tower 3 generates upward steam through the reboiler 6 to contact the wastewater in countercurrent, providing vaporization energy. The vinyl chloride in the wastewater is heated and gasified into gas to contact the wastewater, achieving sufficient gas-liquid mass transfer and vinyl chloride gas phase transfer. The vinyl chloride discharged from the top of the wastewater stripping tower 3 is recycled by the vinyl chloride gas cabinet 4; Step 2: After the wastewater is stripped by the wastewater stripping tower 3, it enters the wastewater neutralization tank 7 for neutralization. The wastewater cooler 5 performs indirect heat exchange cooling on the stripped wastewater. The neutralized wastewater supernatant passes through the primary sedimentation tank 9 and the secondary sedimentation tank 10 in turn 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 clean 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 water inlet tank 18 in turn and is treated by the reverse osmosis device 21, the RO water production tank 22 and multiple mixed beds 26. The water with qualified indicators is sent to the circulating water tank 27 for recycling, and the concentrated water treated by the reverse osmosis device 21 is sent to the primary sedimentation tank 9 for further recycling.

[0018] A nitrogen pipeline 37, a hydrochloric acid pipeline 36 and a vent pipe 28 are respectively provided at the top of the wastewater neutralization tank 7, and the nitrogen pipeline 37 leads to the bottom of the wastewater neutralization tank 7; a clean water pump 15 and a backwash pump 16 are respectively connected to the bottom of the clean water tank 14, the output end of the clean water pump 15 is connected to the top of the first activated carbon filter 171 and the second activated carbon filter 172 and is provided with a valve A39, and a valve B40 is provided on the input end of the RO water inlet tank 18; 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 primary sedimentation tank 9 and is provided with a valve C41, and a valve D42 is provided on the output end of the backwash pump 16; During normal operation of the device, by opening valve A39 and valve B40, and closing valve C41 and valve D42, the wastewater in the clean water tank 14 is filtered through the first activated carbon filter 171 and the second activated carbon filter 172; by opening valve C41 and valve D42, and closing valve A39 and valve B40, the first activated carbon filter 171 and the second activated carbon filter 172 are backwashed, and the wastewater after backwashing is sent to the primary sedimentation tank 9 for further recovery and treatment.

[0019] A frame filter press 13 is provided between the sludge tank 11 and the clean water tank 14; a safety filter 20 is connected between the RO water inlet tank 18 and the reverse osmosis device 21; a decarbonization tower 23 is provided on the RO water production tank 22, and a blower 24 is provided 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.

[0020] Embodiment 1, Wastewater tank 1 is equipped with a steel-lined PTFE storage tank. Since the feed wastewater carries vinyl chloride, there is a safety risk. A closed storage tank is required for temporary buffer storage of the wastewater. The design needs to comprehensively consider safety, operability, environmental protection, and durability to ensure stability during the storage process and reduce the risk of accidents.

[0021] A waste alkali water inlet pipe 34 is arranged on the top of the wastewater tank 1, and a valve control is arranged on the waste alkali water inlet pipe 34. The purpose of setting the wastewater tank 1 is to ensure the continuous operation of the wastewater stripping device and temporarily store the waste alkali liquid from the vinyl chloride alkali washing tower. An outlet pipe is arranged at the bottom of the wastewater tank 1 to connect the wastewater stripping pump 2, and the wastewater stripping pump 2 is connected to the feed port of the wastewater stripping tower 3 through a pipe to send the wastewater to the wastewater stripping tower 3. The wastewater stripping tower 3 is designed as a stainless steel sieve plate tower. The wastewater tank 1, the wastewater stripping pump 2 and the inlet and outlet pipes are required to use stainless steel to avoid corrosion of the waste alkali liquid.

[0022] The bottom of the wastewater stripping tower 3 is connected to a reboiler 6, which 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 a pipeline to form a loop connection. The shell side inlet of the reboiler 6 is designed with a steam pipe 32 to pass steam for heating, and the shell side condensate outlet is designed with a condensate collection pipe 33. The wastewater is sent to the upper part of the tower through the wastewater stripping pump 2 and enters the wastewater stripping tower 3. Steam is passed into the shell side of the reboiler 6 at the bottom for heating. The upward steam generated at the bottom of the wastewater stripping tower 3 contacts the wastewater in countercurrent to provide vaporization energy. The vinyl chloride in the wastewater is heated and vaporized into gas. The vinyl chloride gas phase contacts the wastewater through the tower plate to achieve sufficient gas-liquid mass transfer and vinyl chloride gas phase transfer. The vinyl chloride discharged from the top of the wastewater stripping tower 3 is transported to the vinyl chloride gas holder 4 in the main process production device through a pipeline for recycling.

[0023] The design of the wastewater stripping tower 3 requires the control of the stripping tower temperature, pressure, liquid level, gas flow rate and other parameters to ensure stripping efficiency, avoid overheating, overload and ensure continuous production. After passing through the wastewater stripping tower 3, the vinyl chloride in the wastewater is effectively separated, realizing the recycling of vinyl chloride in the wastewater. The vinyl chloride gas holder 4 is a storage device in the vinyl chloride purification process, which adjusts the imbalance between supply and demand between production and consumption, stores excess, ensures continuous and stable production, and avoids production interruption or excessive discharge.

[0024] A wastewater cooler 5 is arranged at the bottom of the wastewater stripping tower 3. 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, the stripped wastewater is controlled by liquid level to pass through the designed height difference and enter the wastewater neutralization tank 7 from the top pipe of the wastewater neutralization tank 7. The shell inlet of the wastewater cooler 5 is cooled by circulating water through the circulating water upper water pipe 30, and the outlet is cooled through 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 perform indirect heat exchange cooling on the stripped wastewater with circulating water. The steam condensed water of the reboiler 6 flows to the wastewater tank 1 through the condensed water collecting pipe 33. Since the temperature of the steam condensed water is relatively high, it flows to the wastewater tank 1 to directly heat the wastewater in advance of the steam, thereby reducing the heat loss of the wastewater stripping tower 3 and realizing heat recovery.

[0025] The wastewater neutralization tank 7 is designed as a stainless tube storage tank, specifically a steel-lined PTFE storage tank, and the lining needs to be periodically tested for electric sparks to prevent corrosion and leakage. A nitrogen pipeline 37 is set at the top of the wastewater neutralization tank 7 to the bottom of the wastewater neutralization tank 7, and a hydrochloric acid pipeline 36 is designed at the top. The design concentration of hydrochloric acid addition is required to be 18%-22%. By adding hydrochloric acid to the wastewater neutralization tank 7 and turning on nitrogen stirring to ensure that the acid-base neutralization reaction is complete, the wastewater neutralization tank 7 needs to be designed with a PH value online detection and display device to facilitate timely adjustment of the amount of hydrochloric acid added. In order to avoid the pressure holding situation during the nitrogen purging and stirring of the wastewater neutralization tank 7, a vent pipe 28 is set at the top of the wastewater neutralization tank 7 to facilitate the discharge of nitrogen during the nitrogen stirring process of the wastewater neutralization tank 7, so as to control the PH value of the waste alkali solution in the wastewater neutralization tank 7 to be stable between 7-9.

[0026] An outlet is arranged at the bottom of the wastewater neutralization tank 7, which is connected to the sedimentation pump 8 through a pipeline. The outlet of the sedimentation pump 8 transports the neutralized wastewater in the wastewater neutralization tank 7 to the primary sedimentation tank 9 through a pipeline. The wastewater enters the bottom of the sedimentation tank from one side of the primary sedimentation tank 9, and flows to the subsequent treatment process through the overflow port at the top of the other side. A coagulant is quantitatively added at the top of the primary sedimentation tank 9 through a coagulant pipeline 29. Through charge neutralization, compression of the double electric layer and other effects, the stability of the suspended particles is destroyed, and the repulsive force between the particles is weakened, so as to prepare for the subsequent flocculation process. Most flocculants are mainly polyaluminum chloride. After being added to the water, multivalent cations are released to neutralize the charge of the negatively charged suspended particles in the water, thereby reducing the electrostatic repulsion between the particles, making it easy for the suspended matter to aggregate and settle, and then the chloride salt suspended matter contained in the wastewater is deposited at the bottom of the sedimentation tank and flows 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. During the design process, the primary sedimentation tank 9, the secondary sedimentation tank 10, the sludge tank 11 and the clear water tank 14 are sequentially provided with high head differences, and the wastewater supernatant can realize gravity sedimentation flow through the high head difference, and flow to the clear water tank 14 after passing through the primary sedimentation tank 9 and the secondary sedimentation tank 10 in sequence.

[0027] 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, degrade pollution, and improve water quality. At the same time, suspended matter in the wastewater (chloride salts, silt, soil, biosolids, suspended organic matter) is settled to the bottom, and the supernatant overflows to remove suspended matter.

[0028] The structural principle of the secondary sedimentation tank 10 is the same as that of the primary sedimentation tank 9. A flocculant pipeline 35 is set at the top of the secondary sedimentation tank 10 to quantitatively add flocculants to further promote and optimize the growth and coagulation of the initially formed flocs, making them more stable, larger and easier to settle. The flocculant usually used is polyacrylamide. The settled suspended matter is discharged to the sludge tank 11 through the bottom pipeline, and the supernatant overflows to the clear water tank 14 through the other side of the top of the secondary sedimentation tank 10. The design volume of the primary sedimentation tank 9 and the secondary sedimentation tank 10 must meet the sedimentation requirements, and the dosage of coagulants and flocculants must be calculated according to the production requirements.

[0029] The bottom of the sludge pool 11 is connected to a sludge pump 12 through a pipeline, and the sludge is transported to a frame filter press 13 for filtration. After filtration, the sludge passes through a collecting tank, is dried and collected, and is processed as a mercury-containing sludge process. The clear liquid from the frame filter press 13 is transported to a clear water pool 14 for the next step of processing.

[0030] An outlet pipe is provided at the bottom of the clean water tank 14, and is connected to the clean water pump 15 and the backwash pump 16 through a tee pipe. A pipe is provided at the outlet of the clean water pump 15 to transport the wastewater from the clean water tank 14 to two activated carbon filters for filtration. The wastewater filtered by the first activated carbon filter 171 and the second activated carbon filter 172 enters the RO water inlet tank 18 for temporary storage. Two activated carbon filters are provided to operate in parallel, and activated carbon is filled inside. The wastewater can effectively absorb the residual chloride in the water, such as sodium chloride, through the activated carbon filter, to protect the subsequent reverse osmosis device 21, to improve the equipment life, and to reduce disinfection by-products.

[0031] The first activated carbon filter 171 and the second activated carbon filter 172 can realize the switching operation of filtering and backwashing by setting valves. During normal operation, valves A39 and B40 are opened, valves C41 and D42 are closed, and the wastewater in the clean water tank 14 is filtered through the activated carbon filter by the clean water pump 15. Since the waste alkaline water containing vinyl chloride is transported intermittently, the activated carbon filter can be backwashed when the conveying process of the front-stage system is stopped. By opening valves C41 and D42, closing valves A39 and B40, the activated carbon filter is backwashed using the backwash pump 16. The backwashing wastewater of the activated carbon filter is transported to the primary sedimentation tank 9 through a pipeline for further recycling and treatment. The activated carbon filter can be operated intermittently according to production, or the reference pressure difference of the inlet and outlet pressure gauges can be set for backwashing.

[0032] The wastewater filtered by the first activated carbon filter 171 and the second activated carbon filter 172 enters the RO water inlet tank 18. The RO water inlet tank 18 is required to be made of stainless steel, and the design of the water tank volume and other aspects must match the capacity of the subsequent reverse osmosis device 21. An outlet is set at the bottom of the RO water inlet tank 18, which is connected to the RO water inlet pump 19 through a pipeline. The RO water inlet pump 19 is connected to the security filter 20 through a pipeline. The security filter 20 is mainly used to remove fine particles (0.1-5 microns), protect the RO membrane, prevent scratches, extend the service life of the RO membrane, remove particles and colloids in the water, improve the clarity of the inlet water, ensure efficient RO penetration, reduce fouling and membrane pollution, and improve water production and water quality.

[0033] The outlet pipe of the security filter 20 is connected to the water inlet of the reverse osmosis device 21. The reverse osmosis device 21 mainly uses a semipermeable membrane, selective permeability, allows water molecules to pass through, blocks macromolecules, ions, organic matter, bacteria, viruses, etc., and efficiently separates water from impurities. After the wastewater from the outlet of the security filter 20 is treated by the reverse osmosis device 21, the concentrated water outlet of the reverse osmosis device 21 is transported to the primary sedimentation tank 9 through the concentrated water pipeline 38 for further recycling. The water produced by the reverse osmosis device 21 is transported to the RO water production tank 22 through a pipeline. A decarbonization tower 23 is set at the top of the RO water production tank 22, and a blower 24 is set at the bottom of the decarbonization tower 23. The water produced from the reverse osmosis device 21 flows to the RO water production tank 22 through the top of the decarbonization tower 23. During operation, the decarbonization tower 23 is blown in reverse by the blower 24 to remove carbon dioxide from the RO water production, thereby reducing the production load of the subsequent mixed bed 26 device. The purpose of setting the decarbonization tower 23 is that carbon dioxide reacts with water to form carbonic acid, which leads to a decrease in the pH value of the inlet water, affects the capacity of the resin exchange, and reduces the efficiency.

[0034] An outlet is set at the bottom of the RO water production tank 22, which is connected to the mixed bed water inlet pump 25 through a pipeline. The RO water is pumped to the two mixed beds 26 for treatment. The mixed bed 26 needs to be designed with an acid-base regeneration device. Anionic and cation resins are added inside the mixed bed 26. The cation resin attracts and removes cations (such as sodium, calcium, and magnesium), and the anion resin absorbs anions (such as chloride and sulfate). When water passes through the mixed bed 26, the cation and anion resins are mixed and interspersed with each other, and the reactions are carried out almost simultaneously, and the ions in the water are removed by rapid exchange. At the same time, the H + OH - Immediately combine, rarely form counter ions, reduce the impact of counter ions, exchange thoroughly, and treat good water quality. Through the cation resin in the mixed bed 26, ion exchange is carried out to further remove the influent ions such as calcium and magnesium in the RO produced water, ensuring that the conductivity of the treated wastewater is ≤10US / CM. After passing through the mixed bed 26, the wastewater is sent to the circulating water pool 27 for water replenishment.

[0035] By applying the above method and the device used, efficient recovery of waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide method can be achieved, vinyl chloride can be recycled and utilized, and zero discharge of waste water can be achieved. The device used in this method is a device for recovering flammable and explosive media. The design and installation must comply with chemical fire and explosion protection requirements, and nitrogen must be used for replacement before the device is put into operation.

Claims

1. A method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide process, characterized in that: The structure of the device used is as follows, comprising a wastewater tank (1), wherein the 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 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 commonly connected to a sludge tank (11), and the secondary sedimentation tank (11) is connected to a sludge tank (12). 0) is connected to a clean water tank (14), the clean water tank (14) is respectively 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 commonly connected to an RO water inlet tank (18), the RO water inlet tank (18) is sequentially connected to a reverse osmosis device (21), an RO water production tank (22), a plurality of mixed beds (26) and a circulating water tank (27), and the reverse osmosis device (21) is also connected to a primary sedimentation tank (9); The method comprises the following steps: Step 1: sending the alkali-containing wastewater in the wastewater tank (1) to the wastewater stripping tower (3) for stripping; the bottom of the wastewater stripping tower (3) generates upward steam through a reboiler (6) to contact the wastewater in countercurrent flow, thereby providing vaporization energy; the vinyl chloride in the wastewater is heated and vaporized into gas to contact the wastewater, thereby achieving sufficient gas-liquid mass transfer and vinyl chloride gas phase transfer; the vinyl chloride discharged from the top of the wastewater stripping tower (3) is recycled by the vinyl chloride gas holder (4); Step 2: After stripping, the wastewater in the wastewater stripping tower (3) enters the wastewater neutralization tank (7) for neutralization. The wastewater cooler (5) performs indirect heat exchange cooling on the stripped wastewater. The neutralized wastewater supernatant passes through the primary sedimentation tank (9) and the secondary sedimentation tank (10) in sequence for sedimentation treatment and then enters the clear water tank (14). The unsettled wastewater enters the sludge tank (11); Step 3: The wastewater from the clean water tank (14) is filtered through a first activated carbon filter (171) and a second activated carbon filter (172). The filtered wastewater enters the RO water inlet tank (18) in turn and is treated by a reverse osmosis device (21), an RO water production tank (22) and a plurality of mixed beds (26). The water with qualified indicators is then sent to a circulating water tank (27) for recycling. The concentrated water treated by the reverse osmosis device (21) is sent to a primary sedimentation tank (9) for further recycling.

2. The method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide process according to claim 1, characterized in that: A nitrogen pipeline (37), a hydrochloric acid pipeline (36) and a vent pipe (28) are respectively provided at the top of the wastewater neutralization tank (7), and the nitrogen pipeline (37) leads to the bottom of the wastewater neutralization tank (7).

3. A method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide process according to claim 1 or 2, characterized in that: The bottom of the clean water tank (14) is respectively connected to a clean water pump (15) and a backwash pump (16); the output end of the clean water pump (15) is connected to the top of the first activated carbon filter (171) and the second activated carbon filter (172) and is provided with a valve A (39); the input end of the RO water inlet tank (18) is provided with a 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) are connected to the primary sedimentation tank (9) and are provided with a valve C (41); the output end of the backwash pump (16) is provided with a valve D (42); During normal operation of the device, by opening valve A (39) and valve B (40) and closing valve C (41) and valve D (42), wastewater in the clean water tank (14) is filtered through the first activated carbon filter (171) and the second activated carbon filter (172); by opening valve C (41) and valve D (42) and closing valve A (39) and valve B (40), the first activated carbon filter (171) and the second activated carbon filter (172) are backwashed, and the wastewater after backwashing is sent to the primary sedimentation tank (9) for further recovery and treatment.

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

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

6. The method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by the calcium carbide process according to claim 5, characterized in that: A decarbonization tower (23) is provided on the RO water production tank (22), and a blower (24) is provided at the bottom of the decarbonization tower (23).

7. The method for efficiently recovering waste alkaline water containing vinyl chloride in the synthesis of vinyl chloride by 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 condensed water collection pipe (33).

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