A VC polymerization tail gas recovery system

Abstract

The present invention belongs to the field of energy saving, environmental protection, emission reduction and PVC powder quality improvement, and specifically relates to a VC polymerization tail gas recovery system. The VC polymerization tail gas recovery system includes a recovery gas buffer tank, two parallel recovery filters, a rotary discharge valve, at least one discharge centrifugal pump, at least one compressor, a desalted water pipeline, a stripping pipeline, an evaporative condenser, a monomer buffer tank, at least one delivery pump, at least one safety tank, a regeneration gas heat exchanger, etc. The present invention discharges non-condensable gas with a VC content of less than 8mg / m 3 , meeting the 10mg / m specified in the "Emission Standard of Pollutants for Caustic Soda and Polyvinyl Chloride Industry" GB15581-2016 3 ; The indicators of PVC resin in the original polymerization system are better than those of PVC produced by the original process, and the "fish eye" indicator is reduced by 6-10 / 400cm. 2 ; Taking a 200,000-ton PVC plant as an example, the ice machine load is reduced by about 7.5*10 5 Kcal / h, saving 858 tons of standard coal per year; therefore, this technology is advanced, reliable and safe in terms of process, product quality and safety.

Description

Technical Field

[0001] The invention belongs to the field of energy saving, environmental protection, emission reduction and PVC powder quality improvement, and specifically relates to a VC polymerization tail gas recovery system. Background Art

[0002] At present, the main methods of VC polymerization to produce PVC include suspension polymerization, emulsion polymerization and bulk polymerization, with suspension polymerization being the main method, accounting for about 80% of the total PVC production. VC monomer undergoes polymerization reaction under various additives. When the monomer conversion rate reaches 80% to 90%, the unreacted monomer needs to be recovered; secondly, in the suspension method and emulsion method, the slurry stripping steam contains up to 15000ppm VC, the VC in the wastewater stripping steam, and the VC in the maintenance replacement steam all need to be recovered; in the bulk polymerization, VC needs to be recovered in the degassing and homogenization system; referring to the suspension polymerization method as an example, the current process does not filter the recovered gas powder, and it enters after being compressed by a water ring vacuum pump, and condenses VC in two-stage shell and tube heat exchangers, and finally enters the recovered monomer storage tank for standby; the vacuum water ring pump discharges VC and powder, and the recovered VC carries powder; secondly, in a domestic PVC production plant, the tail gas of different polymerization methods enters the same storage device, resulting in serious adhesion in the bulk production; resulting in unqualified indicators such as impurities and fish eyes in the product; secondly, the non-condensable gas recovered by the current process contains a high content of VC. If the VC is not completely recovered, it will not only waste resources, but also cause air pollution and human carcinogenesis. Summary of the invention

[0003] In order to solve the deficiencies of the prior art, the present invention provides a VC polymerization tail gas recovery system. The system can be used to recover high-quality VC from tail gas generated by suspension polymerization, bulk polymerization, and emulsion polymerization. The recovered VC can be mixed and stored without affecting the quality of PVC. The process uses intermediate product gas as the power for cleaning and conveying filter materials, does not introduce new back-blowing gas, and uses VC gas phase conveying powder or centrifugal pump conveying slurry as the power to prevent new impurities from appearing in the recovered VC. Finally, VC in VC polymerization tail gas can be recovered to the maximum extent. Reduce tail gas emissions, reduce ice machine cooling consumption, reduce VC polymerization production costs, and improve PVC production quality.

[0004] The technical solution provided by the present invention is as follows:

[0005] A VC polymerization tail gas recovery system, comprising a recovery gas buffer tank, at least one recovery filter, a rotary discharge valve, at least one discharge centrifugal pump, at least one compressor, a desalted water pipeline and a stripping pipeline, wherein the recovery gas buffer tank has a first air inlet, a first air outlet, a first backwashing port, a first discharge port and a first return port, the recovery filter has a second air inlet, a second air outlet, a second backwashing port and a second discharge port, and each compressor has a third air inlet and a third air outlet, wherein:

[0006] The first air outlets are respectively connected to the second air inlets, the second air outlets are respectively connected to the third air inlets, the third air outlets are respectively connected to the second backwash ports and the first backwash ports, and the third air outlets are also sequentially connected to the evaporative condenser and the monomer buffer tank, and the monomer buffer tanks are respectively connected to at least one delivery pump;

[0007] The desalted water pipeline is respectively connected to the first backwash port and each of the second backwash ports, the first discharge port is respectively connected to each of the discharge centrifugal pumps and the rotary discharge valve, each of the second discharge ports is respectively connected to the first return port and the rotary discharge valve, and each of the discharge centrifugal pumps and the rotary discharge valve is respectively connected to the stripping pipeline.

[0008] Based on the above technical solution, the system can process powder stripping gas and polymerization recovery gas of the bulk method, and can also process slurry stripping gas, wastewater stripping gas and polymerization recovery gas of the suspension method.

[0009] A pulse solenoid valve may be provided on the pipelines through which the third air outlet is respectively connected to the second backwashing ports and the first backwashing ports.

[0010] Further:

[0011] The first discharge port is respectively connected to each of the discharge centrifugal pumps or the rotary discharge valve through a first three-way switching valve;

[0012] Each of the second feed ports is connected to the first return feed port or the rotary feed valve through a second three-way switching valve.

[0013] Based on the above technical solution:

[0014] Switch the first three-way switching valve to the recovery gas buffer tank to connect to the discharge centrifugal pump, and switch the second three-way switching valve to the recovery filter to connect to the recovery gas buffer tank. The system can process the slurry stripping gas, wastewater stripping gas and polymerization recovery gas of the suspension method;

[0015] Switch the first three-way switching valve to the recovery gas buffer tank to connect to the rotary discharge valve, and switch the second three-way switching valve to the recovery filter to connect to the rotary discharge valve. The system can process the powder stripping gas and polymerization recovery gas of the bulk method.

[0016] Furthermore, the desalted water pipeline is sequentially connected to the first switch valve and one end of the backwash pipe, the third air outlet is sequentially connected to the second switch valve and the other end of the backwash pipe, and the backwash pipe is respectively connected to the first backwash port and each of the second backwash ports.

[0017] Based on the above technical solution, the main body method and the suspension method can share a backwash pipeline. The first switch valve opens and the second switch valve is closed, which can be used for the suspension method. The first switch valve is closed and the second switch valve is opened, which can be used for the main body method.

[0018] Furthermore, the system also includes a safety tank and a regeneration gas heat exchanger, the high-temperature gas outlet of the regeneration gas heat exchanger is connected to the safety tank, the evaporative condenser has a fourth air inlet, a fourth air outlet, a fourth liquid inlet and a fourth liquid outlet, the third air outlet is connected to the fourth air inlet, the fourth liquid outlet is connected to the monomer buffer tank, the desalted water pipeline is connected to the fourth liquid inlet, the fourth air outlet is connected to the third air inlet and the safety tank respectively through a third three-way switching valve, and the safety tank is then connected to the third air inlet or the venting pipe respectively through a fourth switch valve.

[0019] Furthermore, the monomer buffer tank has an exhaust port, which is connected to the third air inlet. The connecting pipeline can be provided with a one-way valve.

[0020] Based on the above technical solution, the system can further process the exhaust gas of the evaporative condenser and the exhaust gas of the monomer buffer tank.

[0021] Furthermore, the third gas outlet is connected to the third switch valve and the outlet of the rotary discharge valve in sequence. A one-way valve can be provided on the connecting pipeline.

[0022] Based on the above technical solution, the compressor exhaust gas can be used to promote the unloading of the rotary unloading valve.

[0023] Specifically, the recovered gas buffer tank includes a buffer tank body, and a capture net is horizontally arranged on the upper part of the buffer tank body, the first air inlet, the first feed outlet and the first return port are all located below the capture net, and the first air outlet and the first backwash port are both located above the capture net.

[0024] Furthermore, the buffer tank body is cylindrical, and the first air inlet is arranged along its tangent direction.

[0025] Furthermore, a stirring device is provided at the bottom of the buffer tank.

[0026] Based on the above technical solution, it is beneficial to use the suspension method.

[0027] Specifically, the recovery filter includes a tank body, in which a plurality of filter tubes with upper ends opened and lower ends closed are vertically arranged, the upper end opening of each filter tube penetrates a fixed flower plate and is fixedly connected to the fixed flower plate, a backblowing pipe is fixedly arranged above the fixed flower plate through a fixed frame, the backblowing pipe is provided with a plurality of nozzles, each of the nozzles is arranged one by one above the upper end opening of each filter tube, the second air inlet is connected to the lower space of the tank body, the second air outlet is connected to the upper space of the tank body, the second backwashing port is connected to the backblowing pipe, and the second discharge port is connected to the bottom of the tank body.

[0028] Furthermore, the tank body is cylindrical, and the filter tubes are arranged around its circumference to form multiple circles of circular rings with gradually increasing radius, and the filter tubes in each circle are evenly spaced around the circumference.

[0029] Based on the above technical solution, each filter tube can be back-blown and sucked efficiently.

[0030] Furthermore, the lower part of the tank body is in a semi-gourd shape, and its diameter is larger than the diameter of the tank body.

[0031] Based on the technical solution of the present invention, the VC content of the discharged non-condensable gas is lower than 8mg / m 3 , meeting the 10mg / m specified in the "Caustic Soda and Polyvinyl Chloride Industrial Pollutant Emission Standard" GB15581-2016 3 ; After the recycled VC is reused in the original polymerization system under the same conditions, taking the suspension method as an example, the various indicators of PVC resin are better than those of PVC produced by the original process, especially the "fish eye" indicator, which is 6-10 / 400cm lower than the original 2 ; In the plant area of ​​enterprises with bulk, emulsion and suspension polymerization methods, the recovered VC can be mixed and stored, which solves the problem of sticking to the kettle due to the recycled gas from bulk polymerization and emulsion polymerization, and reduces the one-time engineering investment of building storage tanks and gas cabinets for storage; secondly, this technology solves the safety hazard of VC entering the chilled water system due to leakage of heat exchanger tubes in traditional technology to large equipment; economically, this technology reduces the load of the chiller by about 7.5*10 5 Kcal / h, saving 858 tons of standard coal per year; therefore, this technology is advanced, reliable and safe in terms of process, product quality and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a system diagram of the VC polymerization tail gas recovery system provided by the present invention.

[0033] Figure 2 It is a structural schematic diagram of the VC polymerization tail gas recovery system provided by the present invention.

[0034] Figure 3 It is a structural schematic diagram of a recovery filter of a VC polymerization tail gas recovery system provided by the present invention.

[0035] Figure 4 This is a top view of the recovery filter taken along the AA line.

[0036] Attached Figure 1 , 2 , 3, and 4, the structures represented by each number are listed as follows:

[0037] 1. Recovery gas buffer tank, 2. Recovery filter, 3. Rotary discharge valve, 4. Discharge centrifugal pump, 5. Compressor, 6. Desalted water pipeline, 7. Stripping pipeline, 8. Evaporative condenser, 9. Monomer buffer tank, 10. Delivery pump, 11. Safety tank, 12. Regeneration gas heat exchanger, 13. First three-way switching valve, 14. Second three-way switching valve, 15. Third three-way switching valve, 16. Fourth switch valve, 17. First switch valve, 18. Second switch valve, 19. Third switch valve. DETAILED DESCRIPTION

[0038] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0039] In a specific embodiment, Figure 1 , 2 As shown, the VC polymerization tail gas recovery system includes a recovery gas buffer tank 1, two parallel recovery filters 2, a rotary discharge valve 3, at least one discharge centrifugal pump 4, at least one compressor 5, a desalted water pipeline 6, a stripping pipeline 7, an evaporative condenser 8, a monomer buffer tank 9, at least one delivery pump 10, at least one safety tank 11, and a regeneration gas heat exchanger 12.

[0040] In one embodiment, the average particle size of PVC particles is 160 μm, and the distribution thereof is 3-63 μm=1%, 88-74 μm=4%, 97-88 μm=1%, 105-97 μm=9%, 125-105 μm=5%, 150-125 μm=29%, 200-150 μm=49%, (greater than) 200 μm=1%. According to the above distribution, a capture net with a filtration accuracy of 50 μm is set in the recovery gas buffer tank 1, and the air intake mode is set to tangential air intake to ensure that the gas has a certain residence time, so that 95% of the powder is intercepted; The bottom stirring is set in the recovery gas buffer tank. Since the slurry stripping gas will bring part of the water vapor into the feed, the condensed slurry is prevented from settling; (the main body method does not require bottom stirring, flushing water, and discharge pump; the discharge method is changed to a rotary discharge valve, and the product gas after the compressor is sent to the main body degassing system to recover the powder, and the operation is intermittent) The pressure level of the recovery gas buffer tank is set to 2.5MPa, the buffer tank body and the capture net are made of 316L, and the top can be equipped with a safety valve, a liquid level gauge and a liquid level remote transmission; the discharge centrifugal pump adopts an open impeller centrifugal pump, which is operated intermittently to prevent plasticizers from damaging the discharge pump. The basic material is 316.

[0041] In one embodiment, the first discharge port is connected to each of the discharge centrifugal pumps 4 or the rotary discharge valve 3 through the first three-way switching valve 13; each of the second discharge ports is connected to the first return port or the rotary discharge valve 3 through the second three-way switching valve 14. Based on this technical solution: the first three-way switching valve 13 is switched to the recovery gas buffer tank to connect to the discharge centrifugal pump, and the second three-way switching valve 14 is switched to the recovery filter to connect to the recovery gas buffer tank. The system can process the slurry stripping gas, wastewater stripping gas and polymerization recovery gas of the suspension method; the first three-way switching valve 13 is switched to the recovery gas buffer tank to connect to the rotary discharge valve, and the second three-way switching valve 14 is switched to the recovery filter to connect to the rotary discharge valve. The system can process the powder stripping gas and polymerization recovery gas of the bulk method.

[0042] In one implementation, two recovery filters are connected in parallel, and their appearance is "gourd-shaped", mainly composed of annular backwashing and backwashing internals (each nozzle is facing the filter element, which can better backwash or backwash, and the main body is not provided with flushing water), 3μm filtration accuracy filter element, tangential air inlet, safety valve, level meter, etc. Figure 3 As shown,

[0043] The recovery filter can be equipped with pressure detection instruments, switch valves, and electromagnetic pulse valves at the inlet and outlet; if the inlet and outlet pressure difference is greater than 200Pa, it can be switched to another recovery filter to clean the current filter;

[0044] The filter element is made of inner and outer steel frames, with multiple filter materials wound in the middle. The end cap is made of stainless steel to prevent the filter element end from being damaged by the seal. There are steel supports inside and outside to protect the filter element from damage in the case of two-way airflow. The filtration efficiency is 99.99%, making the solid content of tail gas less than ≤0.5mg / m 3 , for example, stainless steel sintered felt filter elements can be selected. Secondly, this fine filtration system can be cleaned without opening the cover all year round, and the filter screen does not need to be replaced for 3 years;

[0045] All metal surfaces of the equipment in contact with the medium are electrolytically polished (including the head ring weld and manhole cover), so that the inner surface roughness of the filter Ra≤0.05μm, the inner surface roughness Ra≤0.1μm; the inner wall of the powder discharge pipeline is polished, and the installation angle with the ground is not less than 60°;

[0046] In one implementation, the rotary discharge valve is mainly used to uniformly discharge the powder in the filter to the air delivery system (the suspension method or emulsion method does not have a rotary discharge valve and an air delivery system, and the powder is discharged to the recovery gas buffer tank).

[0047] In one implementation, two compressors are connected in parallel and a screw compressor is selected to provide a higher compression ratio. The compressor outlet pressure is not less than 0.6 MPa (G). When the pressure reaches 28°C at the outlet of the evaporative condenser, vinyl chloride can be liquefied and separated from the non-condensable gas.

[0048] In one embodiment, the evaporative condenser 8, the U-shaped feed pipe, the body buffer tank 9, the delivery pump 10, the safety tank 11, and the regeneration gas heat exchanger 12 constitute an evaporative condensation system. The evaporative condenser 8 adopts the existing technology and is composed of a variable frequency motor, a tower body, a cooling coil, a circulating water pump, a water collection tank, a non-condensable gas online analyzer, a pressure and temperature detection instrument, a switch valve, etc.

[0049] In one embodiment, the evaporative condenser cooling coil uses a dry air cooling section and a mixed air cooling section to cool the material. The dry cooling section uses aluminum alloy fin tubes, and the wet air section uses a duplex steel tube. The dry and wet sections are made into an integral coil and then hot-soaked. In winter (0°C) when running without water, air is used to achieve the condensation effect.

[0050] In one embodiment, the fan and water pump motors are flameproof motors, installed outdoors, with protection level IP55, explosion-proof level dⅡBT4, and meet the 380V / 50Hz AC power supply requirements. The fan blades are made of aluminum alloy, and the transmission form is direct-connected (high transmission efficiency, energy saving, and maintenance-free).

[0051] In one embodiment, the safety tank is filled with high-efficiency porous adsorption materials, and the materials are filled in layers and intervals to ensure that the exhaust gas passes through the adsorption materials in the safety tank evenly; when the VC in the exhaust gas exceeds the standard, VC is adsorbed immediately to ensure that the VC content of the evacuated non-condensable gas is always less than 8mg / m 3 ; The exhaust pipeline of the safety tank can be conventionally installed with online analyzers, and the VC content is equal to 8mg / m 3 , the safety tank is switched to another one, and the adsorption saturated safety tank is regenerated at the same time. The regeneration gas uses hot nitrogen with a temperature of not less than 0.5MPa(G) and 80-105℃ (the bulk method can use 60-80℃).

[0052] like Figure 2 As shown, the compressor 5 can be composed of two compressor sub-machines connected in parallel, the discharging centrifugal pump 4 can be composed of two sub-pumps connected in parallel, the safety tank 11 can be composed of two sub-tanks connected in parallel, and the delivery pump 10 can be composed of two sub-pumps connected in parallel.

[0053] In one embodiment, Figure 1 , 2 As shown in , 3 and 4, the recovery gas buffer tank 1 has a first air inlet, a first air outlet, a first backwash port, a first feed port and a first return port, the recovery filter 2 has a second air inlet, a second air outlet, a second backwash port and a second feed port, each of the compressors 5 has a third air inlet and a third air outlet, and the evaporative condenser 8 has a fourth air inlet, a fourth air outlet, a fourth liquid inlet and a fourth liquid outlet.

[0054] The first air outlet is connected to each of the second air inlets respectively, each of the second air outlets is connected to the third air inlet respectively, the third air outlet is connected to each of the second backwash ports and the first backwash ports respectively, and is connected to the evaporative condenser 8 and the monomer buffer tank 9 in sequence, and the monomer buffer tank 9 is connected to at least one delivery pump 10 respectively.

[0055] The desalted water pipeline 6 is respectively connected to the first backwash port and each of the second backwash ports, the first feed port is respectively connected to each of the discharge centrifugal pumps 4 and the rotary feed valve 3, each of the second feed ports is respectively connected to the first return port and the rotary feed valve 3, and each of the discharge centrifugal pumps 4 and the rotary feed valve 3 is respectively connected to the stripping pipeline 7. Based on this, the system can process both the powder stripping gas and polymerization recovery gas of the bulk method, and the slurry stripping gas, wastewater stripping gas and polymerization recovery gas of the suspension method.

[0056] The first discharge port is connected to each of the discharge centrifugal pumps 4 or the rotary discharge valves 3 through the first three-way switching valve 13. Each of the second discharge ports is connected to the first return port or the rotary discharge valve 3 through the second three-way switching valve 14. Based on this, the first three-way switching valve 13 is switched to the recovery gas buffer tank to connect the discharge centrifugal pump, and the second three-way switching valve 14 is switched to the recovery filter to connect the recovery gas buffer tank. The system can process the slurry stripping gas, wastewater stripping gas and polymerization recovery gas of the suspension method. Switch the first three-way switching valve 13 to the recovery gas buffer tank to connect the rotary discharge valve, and switch the second three-way switching valve 14 to the recovery filter to connect the rotary discharge valve. The system can process the powder stripping gas and polymerization recovery gas of the bulk method.

[0057] The desalted water pipeline 6 is sequentially connected to the first switch valve 17 and one end of the backwashing pipeline, and the third air outlet is sequentially connected to the second switch valve 18 and the other end of the backwashing pipeline. Based on this, the main body method and the suspension method can share a section of the backwashing pipeline. The first switch valve opens and closes the second switch valve, which can be used for the suspension method. The first switch valve closes and opens the second switch valve, which can be used for the main body method.

[0058] The high-temperature gas outlet of the regeneration gas heat exchanger 12 is connected to the safety tank 11, the third gas outlet is connected to the fourth gas inlet, the fourth liquid outlet is connected to the monomer buffer tank 9, the desalted water pipeline 6 is connected to the fourth liquid inlet, the fourth gas outlet is connected to the third gas inlet and the safety tank 11 through the third three-way switching valve 15, and the safety tank 11 is connected to the third gas inlet or the venting pipeline through the fourth switch valve 16. The two desalted water pipelines 6 are the same pipeline.

[0059] The monomer buffer tank 9 has an exhaust port, which is connected to the third air inlet. The connecting pipeline can be provided with a one-way valve. Based on this, the system can further process the exhaust gas of the evaporative condenser and the exhaust gas of the monomer buffer tank.

[0060] The third gas outlet is connected to the third switch valve 19 and the outlet of the rotary unloading valve 3 in sequence. A one-way valve can be provided in the connecting pipeline. Based on this, the compressor outlet can be used to promote the unloading of the rotary unloading valve.

[0061] The recovered gas buffer tank 1 includes a buffer tank body, a collection net is transversely arranged at the upper part of the buffer tank body, the first air inlet, the first feed outlet and the first return outlet are all located below the collection net, and the first air outlet and the first backwash outlet are both located above the collection net. The buffer tank body is cylindrical, and the first air inlet is arranged along its tangent direction. A stirring device is arranged at the bottom of the buffer tank body. Based on this, it is convenient to use the suspension method.

[0062] The recovery filter 2 includes a tank body 21, in which a plurality of filter tubes 22 with upper openings and lower closed ends are vertically arranged, the upper openings of each filter tube 22 are penetrated by a fixed flower plate and fixedly connected thereto, a back-blowing tube 24 is fixedly arranged above the fixed flower plate through a fixed frame 23, the back-blowing tube 24 is provided with a plurality of nozzles 25, each of the nozzles 25 is arranged one by one above the upper openings of each filter tube 22, the second air inlet is connected to the lower space of the tank body 21, the second air outlet is connected to the upper space of the tank body 21, the second backwashing port is connected to the back-blowing tube 24, and the second feed port is connected to the bottom of the tank body 21. The tank body 21 is cylindrical, and each of the filter tubes 22 is arranged around its circumference into a plurality of circular rings with gradually increasing radius, and the filter tubes 22 in each circle are evenly arranged around the circumference. The lower part of the tank body 21 is a semi-gourd shape, and its diameter is larger than the diameter of the tank body 21. Based on this technical solution, each filter tube 22 can be back-blown and sucked efficiently.

[0063] In order to ensure the capacity of the polymerization process, the VC polymerization tail gas recovery system is designed to recover vinyl chloride gas based on 15% of the polymerization feed amount as polymerization tail gas, which is equivalent to the peak amount recovered at the lowest conversion rate of a batch when the stripping tower is running at the maximum flow rate. It is assumed that the gas entering the vinyl chloride compressor contains 1% (volume basis) inert gas, and these inert gases have the properties of air.

[0064] The VC-containing tail gas from the polymerization kettle, discharge tank system, stripping tower, vacuum pump and wastewater stripping tower system (or bulk degassing system, homogenization system) enters the recovery gas buffer tank 1 (optional model V300) in a tangential form to ensure that the gas has a residence time of more than 2 seconds, so that most of the gas entrained powder is separated again; the suspension method will entrain a small amount of water vapor and settle again. The bottom of the recovery gas buffer tank 1 is stirred to prevent the slurry from hardening. By setting the material level of the liquid level gauge, the bottom of the buffer tank is discharged in time, and the discharge centrifugal pump (type The material is sent to the stripping tower; the inlet and outlet of the recovery buffer tank can be equipped with a pressure detection instrument, and the tail gas pressure difference can be automatically calculated. When the pressure difference is greater than 200Pa, the flushing water is started to flush the capture net powder, and the material is discharged in time according to the material level. The flushing time is not more than 5min, and the flushing water pressure is not less than 0.6MPa(G). The flushing water is set at the top of the buffer tank. The filter screen is cleaned by the 360° nozzle; (If it is the tail gas of the bulk method, the water washing process is not used, and the compressor outlet gas is used to backflush the system, and the aggregate is sent to the degassing tank by the air delivery system);

[0065] The exhaust gas that has been filtered once is discharged from the top of the recovery gas buffer tank 1 and continues to pass through the recovery filter 2 through a 3μm filter element with a filtration efficiency of 99.99%, making the solid content of the exhaust gas less than ≤0.5mg / m3 ; Pressure detection instruments can be set at the inlet and outlet of the fine filter to calculate the pressure difference. When the pressure difference is greater than 150Pa, switch to another one to flush the current one. The flushing water and backwashing gas are used to clean the high-precision filter element in a pulsed form. The backwashing and backwashing time are not more than 5 minutes. The flushing water and backwashing gas pressures are controlled at 0.3MPa(G)-0.5MPa(G). According to the material level, the material is discharged into the recovery filter 2 in time, and the slurry is sent to the stripping according to the buffer tank level; (If it is the tail gas from the bulk method, the water washing process is not used, and the rear end gas of the compressor is used to backwash the system, and the aggregate is sent to the degassing tank by the air conveying system);

[0066] The tail gas after the recovery filter 2 enters the screw compressor, the outlet pressure of the compressor is not less than 0.6MPa(G), the temperature is not higher than 40℃, the compressor is a complete set of equipment, and the heat exchange is contained in the compression boundary area; part of the compressed gas is sent to the evaporative condenser 8 for liquefaction; part of the gas is used as the back-blowing gas of the filter screen of the recovery filter 2 and the recovery gas buffer tank 1, and this operation is intermittent (if the tail gas is from the main body method, the recovery filter 2 is discharged through the rotary discharge valve 3 to enter the air delivery system, and the air delivery gas source comes from the compressor outlet, and this operation is continuous.

[0067] The compressed tail gas enters the evaporative condenser 8. The fan of the evaporative condenser 8 is set to variable frequency to ensure that the VC temperature is always below 28°C. The tail pressure regulating valve is set to adjust according to the inlet pressure of the evaporative condenser to keep the internal pressure of the evaporative condenser heat exchange coil not less than 0.6MPa (G), thus ensuring the liquefaction effect; the non-condensable gas outlet can be equipped with an online monitoring instrument for VC content and a three-way program-controlled valve switch. If the VC content is higher than 8mg / m 3 , the tail gas is no longer discharged to the safety tank, but returns to the compressor inlet and is compressed and condensed again;

[0068] The evaporative condensate enters the monomer buffer tank 9 through the U-shaped tube. The U-shaped tube ensures that the tail gas does not enter the monomer buffer tank 9. The quality of the monomer in the tank is controlled within 1 ton. It is cached on site and not stored to ensure that it does not constitute a major hazard source. The monomer buffer tank 9 can be equipped with a liquid level gauge and a pump outlet regulating valve to ensure that the liquid level of the monomer buffer tank 9 remains within a certain range. The monomer buffer tank 9 can be equipped with safety accessories such as a safety valve and an on-site pressure gauge. Secondly, the gas phase in the monomer buffer tank 9 is connected to the compressor inlet to recover the gas phase vinyl chloride in time, thus ensuring the safe operation of the buffer tank;

[0069] VC content is less than 8mg / m 3 The tail gas enters the safety tank and is discharged to the outside 11. The safety tank 11 can be equipped with an online monitoring instrument for VC content. If the VC content is higher than 8mg / m 3, the safety tank is switched to another one; the adsorption saturated safety tank is regenerated by hot nitrogen, and the exhaust gas after regeneration is sent to the inlet of compressor 5 to recover VC in the regenerated gas; in this way, one safety tank is always in the standby state, thereby ensuring the qualified emission of exhaust gas and the maximum recovery of VC in the exhaust gas.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A VC polymerization tail gas recovery system, characterized by: The invention comprises a recovery gas buffer tank (1), at least one recovery filter (2), a rotary discharge valve (3), at least one discharge centrifugal pump (4), at least one compressor (5), a desalted water pipeline (6) and a stripping pipeline (7), wherein the recovery gas buffer tank (1) has a first air inlet, a first air outlet, a first backwashing port, a first discharge port and a first return port, the recovery filter (2) has a second air inlet, a second air outlet, a second backwashing port and a second discharge port, and each compressor (5) has a third air inlet and a third air outlet, wherein: The first air outlets are respectively connected to the second air inlets, the second air outlets are respectively connected to the third air inlets, the third air outlets are respectively connected to the second backwashing ports and the first backwashing ports, and the third air outlets are also sequentially connected to the evaporative condenser (8) and the monomer buffer tank (9), and the monomer buffer tanks (9) are respectively connected to at least one delivery pump (10); The desalted water pipeline (6) is respectively connected to the first backwash port and each of the second backwash ports, the first discharge port is respectively connected to each of the discharge centrifugal pumps (4) and the rotary discharge valve (3), each of the second discharge ports is respectively connected to the first return port and the rotary discharge valve (3), and each of the discharge centrifugal pumps (4) and the rotary discharge valve (3) is respectively connected to the stripping pipeline (7); The first discharge port is respectively connected to each of the discharge centrifugal pumps (4) or the rotary discharge valve (3) through a first three-way switching valve (13); Each of the second feed ports is connected to the first return feed port or the rotary feed valve (3) via a second three-way switching valve (14); The desalted water pipeline (6) is connected in sequence to the first switch valve (17) and one end of the backwash pipe, the third air outlet is connected in sequence to the second switch valve (18) and the other end of the backwash pipe, and the backwash pipe is connected to the first backwash port and each of the second backwash ports respectively.

2. The VC polymerization tail gas recovery system according to claim 1, characterized in that: The system also includes a safety tank (11) and a regeneration gas heat exchanger (12), wherein the high-temperature gas outlet of the regeneration gas heat exchanger (12) is connected to the safety tank (11), the evaporative condenser (8) has a fourth air inlet, a fourth air outlet, a fourth liquid inlet and a fourth liquid outlet, the third air outlet is connected to the fourth air inlet, the fourth liquid outlet is connected to the monomer buffer tank (9), the desalted water pipeline (6) is connected to the fourth liquid inlet, the fourth air outlet is connected to the third air inlet and the safety tank (11) respectively through a third three-way switching valve (15), and the safety tank (11) is then connected to the third air inlet or the venting pipeline respectively through a fourth switch valve (16).

3. The VC polymerization tail gas recovery system according to claim 2, characterized in that: The monomer buffer tank (9) has an exhaust port connected to the third air inlet; The third air outlet is connected in sequence to the third switch valve (19) and the outlet of the rotary discharge valve (3).

4. The VC polymerization tail gas recovery system according to any one of claims 1 to 3, characterized in that: The recovered gas buffer tank (1) comprises a buffer tank body, a capture net is transversely arranged at the upper part of the buffer tank body, the first air inlet, the first feed outlet and the first return outlet are all located below the capture net, and the first air outlet and the first backwash outlet are both located above the capture net.

5. The VC polymerization tail gas recovery system according to claim 4, characterized in that: The buffer tank body is cylindrical, and the first air inlet is arranged along its tangent direction; A stirring device is arranged at the bottom of the buffer tank.

6. The VC polymerization tail gas recovery system according to any one of claims 1 to 3, characterized in that: The recovery filter (2) comprises a tank body (21), wherein a plurality of filter tubes (22) with an upper end opening and a lower end closed are vertically arranged in the tank body (21), the upper end opening of each filter tube (22) penetrates a fixed flower plate and is fixedly connected thereto, an annular back-blowing pipe (24) is fixedly arranged above the fixed flower plate via a fixing frame (23), the back-blowing pipe (24) is provided with a plurality of nozzles (25), and each nozzle (25) is arranged one by one above the upper end opening of each filter tube (22), the second air inlet is connected to the lower space of the tank body (21), the second air outlet is connected to the upper space of the tank body (21), the second backwashing port is connected to the back-blowing pipe (24), and the second discharge port is connected to the bottom of the tank body (21).

7. The VC polymerization tail gas recovery system according to claim 6, characterized in that: The tank body (21) is cylindrical, and the filter tubes (22) are arranged around its circumference to form a plurality of circular rings with gradually increasing radii, and the filter tubes (22) in each circle are evenly spaced around the circumference.

8. The VC polymerization tail gas recovery system according to claim 6, characterized in that: The lower part of the tank body (21) is in the shape of a circular arc and protrudes outwardly in a semi-gourd shape, and the diameter of the protruding part is larger than the diameter of the tank body (21).

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