A vinyl chloride monomer extraction and dehydration system and dehydration method

Abstract

The present invention provides a vinyl chloride monomer dehydration system and method, comprising a vinyl chloride monomer feed pump, a vinyl chloride monomer filter, a pressure reducing valve, an extraction tower I, a heat exchanger, an extraction tower II, a cooler, an extraction tower III, a separation tower, a vinyl chloride monomer circulation pump and an extraction liquid device, which are connected in sequence; an outlet pipe of the vinyl chloride monomer circulation pump provided with a liquid outlet control valve is connected to the heat exchanger, and the outlet pipe of the heat exchanger is connected to a de-distillation pipe and a feed pipe; the present invention has low cost, high dehydration efficiency, low energy consumption, continuous process operation, easy operation and recycling of the extractant; vinyl chloride liquid phase extraction dehydration can reduce the water content of vinyl chloride monomer to below 200 ppm, solves the problems of high water content in calcium carbide-process vinyl chloride, serious corrosion of pipeline equipment of the distillation system by the generated acidic substances, poor thermal stability of polyvinyl chloride resin, low dielectric properties of the product and subsequent self-polymerization of the pipeline, and achieves higher-level quality improvement requirements for polyvinyl chloride resin.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical separation, and in particular relates to a dehydration system and method for separating free water in vinyl chloride monomer by a physical extraction method. Background Art

[0002] Polyvinyl chloride (PVC), a general-purpose resin, has been widely used in construction, packaging, vehicles, electrical appliances, and daily necessities due to its excellent performance. Currently, over 75% of PVC production in my country uses the calcium carbide process. In calcium carbide-based PVC production, the vinyl chloride monomer contains a significant amount of water, which impacts PVC product quality and yield, as well as equipment and pipelines.

[0003] The presence of water in vinyl chloride has a significant impact on subsequent polymerization and distillation systems. It hydrolyzes low-molecular-weight peroxides (formed by oxygen and vinyl chloride) to produce acidic substances such as hydrogen chloride (which, upon contact with water, transforms into hydrochloric acid), formic acid, and formaldehyde. This leads to the hydrolysis of vinyl chloride monomer into low-polymerization vinyl chloride peroxide. Water also easily generates iron ions, which can cause cellulose dispersants to flocculate, resulting in coarse material and yellowing or black specks in the polymerized resin. Further hydrolysis of peroxides produces hydrogen chloride, which dissolves in water to form acid, corroding equipment and pipelines and lowering the pH of the reaction system. The main impacts of water in monomers on the distillation system include: the accumulation of autopolymers, which can clog distillation equipment and pipelines, requiring maintenance and cleaning, disrupting normal production; the formation of acidic substances, which corrode equipment piping, shortening equipment lifespan and posing safety hazards; and the icing of distillation off-gas condensers, which can affect heat transfer efficiency and increase costs and energy consumption.

[0004] In the calcium carbide-based PVC industry, the vast majority of companies utilize static dehydration, solid caustic soda dryers, and temperature swing adsorption dehydration. Static dehydration requires a settling time, which doesn't meet the company's continuous production requirements. Furthermore, the monomer moisture content doesn't change much after static dehydration. Solid caustic soda desiccant desiccant, commonly used in flake caustic soda, has low mechanical strength and is lightweight, making it easily carried over into the next process. Furthermore, the desiccant easily agglomerates after absorbing water, causing the monomer to drift, making it difficult to ensure a consistent and stable drying effect. As a new dehydration process, temperature swing adsorption dehydration has extremely stringent pressure and temperature control requirements. Due to its high temperature requirements, temperature swing adsorption dehydration requires numerous programmable valves, high automation requirements, and high initial investment.

[0005] Product quality is the soul of an enterprise. The quality of PVC resin depends to a large extent on the quality of the monomer. According to the current status of resin production technology, the water content of vinyl chloride monomer produced by the calcium carbide method is much greater than that produced by the ethylene method. The water content of the monomer and the additive content of the recovered monomer have a certain impact on the improvement of the quality of subsequent products and the layout of diversified product types. Therefore, improving product quality is an effective means to increase market share. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the above-mentioned existing static dehydration and solid alkali dryer dehydration technologies, to provide a vinyl chloride monomer dehydration method with good dehydration effect, low energy consumption, simple process, easy operation and recycling of extractant, in view of the large impact of high water content in vinyl chloride on the polymerization system and distillation system, and to meet the higher product quality requirements of enterprises for PVC resin quality. Another object of the present invention is to provide a system for implementing the method.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0008] One of the technical solutions of the present invention is achieved through the following measures: a vinyl chloride monomer extraction and dehydration system, comprising a vinyl chloride monomer feed pump, a vinyl chloride monomer filter, a pressure reducing valve, an extraction tower I, a heat exchanger, an extraction tower II, a cooler, an extraction tower III, a separation tower, a vinyl chloride monomer circulation pump, and an extracting liquid device, which are sequentially connected; an outlet pipe of the vinyl chloride monomer circulation pump equipped with a liquid outlet control valve is connected to the heat exchanger, the liquid outlet control valve is electrically connected to a vinyl chloride monomer liquid level gauge, and the outlet pipe of the heat exchanger is connected to a de-rectification pipe and a feed pipe; a connecting pipe is provided between the de-rectification pipe and the feed pipe; an extracting liquid collection bag is provided at the lower portion of the separation tower, and is connected to the inlet pipe of the extraction tower I via a lower liquid pump;

[0009] The upper end of the extraction tower III is provided with a vinyl chloride monomer outlet pipe, a vent pipe, a recovery pipe, a nitrogen filling pipe, a pressure remote transmission I, a vinyl chloride monomer liquid level gauge and a vinyl chloride monomer thermometer, and the lower end is provided with a vinyl chloride monomer inlet pipe, an extract liquid level gauge and an extract liquid circulation pipe; the vent pipe is provided with a safety valve connected to the distillation recovery main pipe; the vinyl chloride monomer inlet pipe is provided with an inlet thermometer, the recovery pipe is provided with a recovery valve, the recovery valve is electrically connected to the pressure remote transmission I, and the recovery pipe is connected to the pressure swing adsorption device;

[0010] The cooler is provided with a chilled brine inlet pipe and a chilled brine outlet pipe, the chilled brine inlet pipe is sequentially provided with a water inlet control valve, a pipeline pump and a brine thermometer, a brine connecting pipe is provided between the chilled brine inlet pipe and the chilled brine outlet pipe, the connecting pipe is provided with a brine reflux valve, the water inlet control valve and the brine reflux valve are respectively electrically connected to the inlet thermometer;

[0011] The extraction liquid device includes a low-concentration extraction liquid tank, a low-concentration extraction liquid pump, an extraction liquid storage tank, an extraction liquid replenishment pump and an extraction liquid circulation pump. The top of the low-concentration extraction liquid tank is connected to the extraction liquid circulation pipe via a low-concentration extraction liquid recovery pipe provided with an online density meter and a low-concentration extraction liquid recovery valve; the bottom of the low-concentration extraction liquid tank is pumped to the water alkali washing for reuse; the bottom of the extraction liquid storage tank is connected to the extraction liquid circulation pipe via the extraction liquid replenishment pump; the extraction liquid circulation pipe is connected to the extraction liquid circulation pump inlet, and the extraction liquid circulation pump is connected to the extraction tower I and the extraction tower II respectively via the extraction liquid outlet pipe I and the extraction liquid outlet pipe II, the extraction liquid outlet pipe I is provided with an electrically connected flow meter and replenishment valve I, the extraction liquid outlet pipe II is provided with a replenishment valve II, and the replenishment valve II is electrically connected to the extraction liquid level meter.

[0012] Furthermore, the heat exchanger is a spiral plate heat exchanger, and at least one is provided; the cooler is a plate cooler, and at least one is provided.

[0013] Furthermore, a coil is provided on the outer wall of the low-concentration extraction liquid tank, hot water is filled in the coil, and a vinyl chloride recovery pipe is provided on the top of the low-concentration extraction liquid tank and connected to the pressure swing adsorption device.

[0014] Furthermore, a remote pressure transmitter II and a cut-off valve are provided on the inlet pipe of the extraction tower I after the pressure reducing valve, and the remote pressure transmitter II and the cut-off valve are electrically connected.

[0015] The second technical solution of the present invention is to realize the dehydration method of the vinyl chloride monomer extraction and dehydration system by the following measures, comprising the following steps:

[0016] The first step is filtration and decompression. The crude liquid vinyl chloride monomer with a temperature of 20-30°C, a pressure of 1.0-1.5 MPa and a water content of 600-1500 ppm is filtered through a vinyl chloride monomer filter and then decompressed to 0.2-0.6 MPa through a pressure reducing valve.

[0017] In the second step, the VCM after filtration and decompression enters the extraction tower I and is fully mixed with the extract from the extract circulation pump. The mixed VCM enters the heat exchanger and indirectly exchanges heat with the low-temperature VCM overflowed from the separation tower after extraction and dehydration. The outlet temperature is reduced to about 5°C higher than the inlet temperature of the low-temperature VCM.

[0018] In the third step, the product is mixed and cooled twice, enters the extraction tower II and is fully mixed with the low-temperature extract sent by the extraction liquid circulation pump, then enters the cooler, and undergoes indirect heat exchange with the low-temperature brine to a temperature of -5 to -20°C, and then enters the extraction tower III;

[0019] The fourth step is extraction and dehydration. After staying in extraction tower III for a long enough time, the monomer overflows from the top of extraction tower III, enters the separation tower to further remove residual water, and then enters the heat exchanger to reuse cold energy to reduce energy consumption. Finally, it passes through the vinyl chloride monomer circulation pump, increases the pressure to above 1.2MPa, and is sent to the downstream distillation system.

[0020] The following are further improvements to Technical Solution 2:

[0021] The extract is a sodium hydroxide solution with a density of 1.20-1.25 kg / m 3 The flow meter on the extraction liquid outlet pipe I controls 2 to 5 m 3 / h; the online density meter control value on the low concentration extract recovery pipe is 1.20~1.25Kg / m 3 .

[0022] The vinyl chloride monomer contains water ≤ 200 ppm after dehydration.

[0023] The remote control value of the pressure of the extraction tower III is 0.1 to 0.5 MPa, the control value of the vinyl chloride monomer liquid level meter is 8 to 9 m, the control value of the extract liquid level meter is 3 to 4 m, and the control value of the vinyl chloride monomer thermometer is -5 to -20°C.

[0024] The inlet pipe of the extraction tower I after the pressure reducing valve is provided with an interlocking closing shut-off valve when the pressure is greater than or equal to 0.65 MPa.

[0025] The brine temperature is -32 to -35°C.

[0026] The beneficial effects of the present invention are as follows: a vinyl chloride monomer dehydration system and method provided by the present invention have low cost, high dehydration efficiency, low energy consumption, continuous process operation, easy operation and recycling of the extractant; vinyl chloride liquid phase extraction dehydration can reduce the water content of vinyl chloride monomer to below 200 ppm, thereby solving the problems of high water content in calcium carbide-process vinyl chloride, serious corrosion of pipeline equipment of the distillation system by the generated acidic substances, poor thermal stability of polyvinyl chloride resin, low dielectric properties of the product and subsequent self-polymerization of the pipeline, and achieving higher-level quality improvement requirements for polyvinyl chloride resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the vinyl chloride monomer extraction and dehydration system of the present invention

[0028] Figure 2 Schematic diagram of the structure of the extraction tower III of the present invention

[0029] In the figure: 1. Vinyl chloride monomer feed pump; 2. Vinyl chloride monomer filter; 3. Pressure reducing valve; 4. Extraction column I; 5. Heat exchanger; 6. Extraction Tower II; 7. Cooler; 7-1. Chilled Brine Inlet Pipe; 7-2. Chilled Brine Outlet Pipe; 7-3. Water Inlet Control Valve; 7-4. Pipeline Pump; 7-5. Brine Connecting Pipe; 7-6. Brine Reflux Valve; 7-7. Brine Thermometer; 8. Extraction Tower III; 8-1. Vinyl Chloride Monomer Outlet Pipe; 8-2. Vent Pipe; 8-3. Recovery Pipe; 8-4. Nitrogen Charging Pipe; 8-5. Pressure Transmission I; 8-6. Vinyl Chloride Monomer Level Gauge; 8-7. Vinyl Chloride Monomer Thermometer; 8-8. Vinyl Chloride Monomer Inlet Pipe; 8-9. Extraction Liquid Level Gauge; 8-10. Extraction Liquid Circulation Pipe; 8-11. Safety Valve; 8-12. Inlet Thermometer; 8-13. Recovery Valve; 8-14. Nitrogen Charging Valve; 9. Separation Tower; 9-1 .Extract liquid collection bag; 10. Vinyl chloride monomer circulation pump; 11. Liquid outlet control valve; Vinyl chloride monomer circulation pump outlet pipe; 13. Heat exchanger outlet pipe; 14. De-distillation pipe; 15. Feed pipe; 16. Connecting pipe; 17. Downstream liquid pump; 18. Extraction tower I inlet pipe; 19. Low-concentration extract liquid tank; 20. Low-concentration extract liquid pump; 21. Extract liquid storage tank; 22. Extract liquid replenishment pump; 23. Extract liquid circulation pump; 24. Low-concentration extract liquid recovery pipe; 25. Online density meter; 26. Low-concentration extract liquid recovery valve; 27. Extract liquid outlet pipe I; 28. Extract liquid outlet pipe II; 29. ​​Replenishment valve I; 30. Flow meter; 31. Replenishment valve II; 32. Vinyl chloride recovery pipe; 33. Pressure remote transmission II; 34. Shut-off valve. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to more clearly and accurately understand the technical solutions of the present invention, the following is a detailed explanation by way of examples. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can also derive other drawings based on these drawings without inventive effort. Example

[0031] Example 1, with reference to Figure 1 and Figure 2As shown, the present invention provides a vinyl chloride monomer extraction and dehydration system, comprising a vinyl chloride monomer feed pump 1, a vinyl chloride monomer filter 2, a pressure reducing valve 3, an extraction tower I 4, a heat exchanger 5, an extraction tower II 6, a cooler 7, an extraction tower III 8, a separation tower 9, a vinyl chloride monomer circulation pump 10, and an extracting liquid device, which are sequentially connected; a vinyl chloride monomer circulation pump outlet pipe 12 provided with a liquid outlet control valve 11 is connected to the heat exchanger 5, the liquid outlet control valve 11 is electrically connected to a vinyl chloride monomer liquid level gauge 8-6, and a heat exchanger outlet pipe 13 is connected to a de-distillation pipe 14 and a feed pipe 15; a connecting pipe 16 is provided between the de-distillation pipe 14 and the feed pipe 15, and an extracting liquid collecting bag 9-1 is provided at the lower part of the separation tower 9, which is connected to the extraction tower I inlet pipe 18 via a liquid pump 17;

[0032] The upper end of the extraction tower III 8 is provided with a vinyl chloride monomer outlet pipe 8-1, a vent pipe 8-2, a recovery pipe 8-3, a nitrogen charging pipe 8-4, a pressure remote transmission I 8-5, a vinyl chloride monomer liquid level gauge 8-6 and a vinyl chloride monomer thermometer 8-7, and the lower end is provided with a vinyl chloride monomer inlet pipe 8-8, an extract liquid level gauge 8-9, and an extract circulation pipe 8-10; the vent pipe 8-2 is provided with a safety valve 8-11 connected to the distillation recovery main pipe; the vinyl chloride monomer inlet pipe 8-1 is provided with an inlet thermometer 8-12, the recovery pipe 8-3 is provided with a recovery valve 8-13, the recovery valve 8-13 is electrically connected to the pressure remote transmission I 8-5, and the recovery pipe 8-3 is connected to the pressure swing adsorption; the nitrogen charging pipe 8-4 is provided with a nitrogen charging valve 8-14; the nitrogen charging valve 8-14 is electrically connected to the pressure remote transmission I 8-5;

[0033] The cooler 7 is provided with a chilled brine inlet pipe 7-1 and a chilled brine outlet pipe 7-2, the chilled brine inlet pipe 7-1 is provided with a water inlet control valve 7-3, a pipeline pump 7-4 and a brine thermometer 7-7 in sequence, a brine connecting pipe 7-5 is provided between the chilled brine inlet pipe 7-1 and the chilled brine outlet pipe 7-2, the connecting pipe 7-5 is provided with a brine reflux valve 7-6, the water inlet control valve 7-3 and the brine reflux valve 7-6 are electrically connected to the inlet thermometer 8-12 respectively;

[0034] The extracting liquid device includes a low-concentration extracting liquid tank 19, a low-concentration extracting liquid pump 20, an extracting liquid storage tank 21, an extracting liquid replenishing pump 22 and an extracting liquid circulating pump 23. The top of the low-concentration extracting liquid tank 19 is connected to the extracting liquid circulating pipe 8-10 via a low-concentration extracting liquid recovery pipe 24 provided with an online density meter 25 and a low-concentration extracting liquid recovery valve 26; the bottom of the low-concentration extracting liquid tank 19 is sent to the water alkali washing for reuse via the low-concentration extracting liquid pump 20; the bottom of the extracting liquid storage tank 21 is connected to the extracting liquid circulating pipe 8-10 via the extracting liquid replenishing pump 22; the extracting liquid circulating pipe 8-10 is connected to the inlet of the extracting liquid circulating pump 23, and the extracting liquid circulating pump 23 is connected to the extraction tower I4 and the extraction tower II6 respectively via the extracting liquid outlet pipe I27 and the extracting liquid outlet pipe II28. The extracting liquid outlet pipe I27 is provided with an electrically connected flow meter 30 and a replenishing valve I29, and the extracting liquid outlet pipe II28 is provided with a replenishing valve II31. The replenishing valve II31 is electrically connected to the extracting liquid level meter 8-9.

[0035] Furthermore, the heat exchanger 5 is a spiral plate heat exchanger, and at least one is provided; the cooler is a plate cooler, and at least one is provided.

[0036] Furthermore, a coil is provided on the outer wall of the low-concentration extraction liquid tank 19, and hot water is filled in the coil. A vinyl chloride recovery pipe 32 is provided on the top of the low-concentration extraction liquid tank and connected to the pressure swing adsorption device.

[0037] Furthermore, a remote pressure transmitter II 33 and a cut-off valve 34 are provided on the inlet pipe 18 of the extraction tower I after the pressure reducing valve 3 , and the remote pressure transmitter II 33 and the cut-off valve 34 are electrically connected.

[0038] Example 2, using the vinyl chloride monomer extraction and dehydration method, comprising the following steps:

[0039] In the first step, filtration and decompression, the crude liquid vinyl chloride monomer with a temperature of 20-30°C, a pressure of 1.0-1.5 MPa and a water content of 600-1500 ppm from the upstream condensation separation of most of the water is filtered through the vinyl chloride monomer filter 2 and then decompressed to 0.2-0.6 MPa through the pressure reducing valve 3;

[0040] In the second step, the filtered and decompressed vinyl chloride monomer enters the extraction tower I 4 and is fully mixed with the extract from the extract circulation pump 23. The mixed vinyl chloride monomer enters the heat exchanger 5 and is indirectly heat-exchanged with the low-temperature vinyl chloride monomer overflowed from the separation tower after extraction and dehydration. The outlet temperature is reduced to about 5°C higher than the inlet temperature of the low-temperature vinyl chloride monomer.

[0041] In the third step, the mixture is mixed and cooled for the second time, and then enters the extraction tower II 6 and is fully mixed with the low-temperature extract sent by the extract circulation pump 23, and then enters the cooler 7, and is indirectly heat-exchanged with the low-temperature brine to a temperature of -5 to -20°C, and then enters the extraction tower III 8;

[0042] The fourth step is extraction and dehydration. After staying in the extraction tower III for a long enough time, the monomer overflows from the top of the extraction tower III 8, enters the separation tower 9 to further remove the residual water, and then enters the heat exchanger 5 to reuse the cold energy to reduce energy consumption. Finally, it passes through the vinyl chloride monomer circulation pump 10, is pressurized to above 1.2 MPa, and is sent to the downstream distillation system.

[0043] According to actual needs, the following are further optimization and improvements made to Example 2:

[0044] Furthermore, the extract is a sodium hydroxide solution with a density of 1.20-1.25 kg / m 3， The flow meter on the extraction liquid outlet pipe I27 controls 2 to 5 m 3 / h; the low concentration extract recovery pipe 24 on the online density meter control value is 1.20 ~ 1.25Kg / m 3 .

[0045] Furthermore, the water content of the vinyl chloride monomer after dehydration is ≤200 ppm.

[0046] Furthermore, the pressure remote transmission 8-5 of the extraction tower III controls the value of 0.1 to 0.5 MPa, the vinyl chloride monomer level meter 8-6 controls the value of 8 to 9 m, the extract liquid level meter 8-9 controls the value of 3 to 4 m, and the vinyl chloride monomer thermometer 8-7 controls the value of -5 to -20°C.

[0047] Furthermore, after the pressure reducing valve 3, the extraction tower I inlet pipe 18 is provided with a pressure remote transmission 33 ≥ 0.65 MPa, which interlocks and closes the cut-off valve 34.

[0048] Furthermore, the brine temperature is -32 to -35°C.

[0049] Principle of the present invention:

[0050] The lower the temperature, the lower the water content in vinyl chloride. However, even at 0°C, the freezing point of water, the water content in vinyl chloride remains as high as 500 ppm. To further lower the temperature of vinyl chloride monomer without freezing, aqueous solutions of certain substances, such as calcium chloride, sodium chloride, magnesium chloride, sodium bromide, and sodium hydroxide, are added. This significantly lowers the freezing point of water, preventing it from freezing at temperatures of 10 to 20°C below zero, allowing the vinyl chloride to fully contact these substances. The vinyl chloride monomer is then separated from the substances, reducing the water content in the vinyl chloride monomer to below 200 ppm by weight. This method of vinyl chloride monomer purification operates in a closed, continuous process, generating no pollutants.

[0051] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A vinyl chloride monomer extraction and dehydration system, characterized by: The invention comprises a vinyl chloride monomer feed pump, a vinyl chloride monomer filter, a pressure reducing valve, an extraction tower I, a heat exchanger, an extraction tower II, a cooler, an extraction tower III, a separation tower, a vinyl chloride monomer circulation pump and an extracting liquid device, which are sequentially connected; the outlet pipe of the vinyl chloride monomer circulation pump provided with a liquid outlet control valve is connected to the heat exchanger, the liquid outlet control valve is electrically connected to a vinyl chloride monomer liquid level gauge, the outlet pipe of the heat exchanger is connected to a derectification pipe and a feed pipe; a connecting pipe is provided between the derectification pipe and the feed pipe; an extracting liquid collecting bag is provided at the lower part of the separation tower, which is connected to the inlet pipe of the extraction tower I via a lower liquid pump; the heat exchanger is a spiral plate heat exchanger, and at least one is provided; The upper end of the extraction tower III is provided with a vinyl chloride monomer outlet pipe, a vent pipe, a recovery pipe, a nitrogen filling pipe, a pressure remote transmission I, a vinyl chloride monomer liquid level gauge and a vinyl chloride monomer thermometer, and the lower end is provided with a vinyl chloride monomer inlet pipe, an extract liquid level gauge and an extract liquid circulation pipe; the vent pipe is provided with a safety valve connected to the distillation recovery main pipe; the vinyl chloride monomer inlet pipe is provided with an inlet thermometer, the recovery pipe is provided with a recovery valve, the recovery valve is electrically connected to the pressure remote transmission I, and the recovery pipe is connected to the pressure swing adsorption device; The cooler is provided with a chilled brine inlet pipe and a chilled brine outlet pipe, the chilled brine inlet pipe is provided with a water inlet control valve, a pipeline pump and a brine thermometer in sequence, a brine connecting pipe is provided between the chilled brine inlet pipe and the chilled brine outlet pipe, the connecting pipe is provided with a brine reflux valve, the water inlet control valve and the brine reflux valve are electrically connected to the inlet thermometer respectively; the cooler is a plate-type cooler, at least one of which is provided; The extraction liquid device includes a low-concentration extraction liquid tank, a low-concentration extraction liquid pump, an extraction liquid storage tank, an extraction liquid replenishment pump and an extraction liquid circulation pump. The top of the low-concentration extraction liquid tank is connected to the extraction liquid circulation pipe via a low-concentration extraction liquid recovery pipe provided with an online density meter and a low-concentration extraction liquid recovery valve; the bottom of the low-concentration extraction liquid tank is pumped to water alkali washing for reuse; a coil is provided on the outer wall of the low-concentration extraction liquid tank, and hot water is filled in the coil. A vinyl chloride recovery pipe is provided on the top of the low-concentration extraction liquid tank, which is connected to a pressure swing adsorption device; the bottom of the extraction liquid storage tank is connected to the extraction liquid circulation pipe via the extraction liquid replenishment pump; the extraction liquid circulation pipe is connected to the extraction liquid circulation pump inlet, and the extraction liquid circulation pump is connected to extraction tower I and extraction tower II respectively via extraction liquid outlet pipe I and extraction liquid outlet pipe II, the extraction liquid outlet pipe I is provided with an electrically connected flow meter and replenishment valve I, the extraction liquid outlet pipe II is provided with replenishment valve II, and the replenishment valve II is electrically connected to the extraction liquid level meter; the extraction liquid used in the extraction liquid device is sodium hydroxide solution.

2. A vinyl chloride monomer extraction and dehydration system according to claim 1, characterized in that: A pressure remote transmission II and a cut-off valve are provided on the inlet pipe of the extraction tower I after the pressure reducing valve, and the pressure remote transmission II and the cut-off valve are electrically connected.

3. The dehydration method of the vinyl chloride monomer extraction and dehydration system according to any one of claims 1 to 2, characterized in that: The following steps are involved: The first step is filtration and decompression. The crude liquid vinyl chloride monomer with a temperature of 20-30°C, a pressure of 1.0-1.5 MPa and a water content of 600-1500 ppm is filtered through a vinyl chloride monomer filter and then decompressed to 0.2-0.6 MPa through a pressure reducing valve. In the second step, the VCM after filtration and decompression enters the extraction tower I and is fully mixed with the extract from the extract circulation pump. The mixed VCM enters the heat exchanger and indirectly exchanges heat with the low-temperature VCM overflowed from the separation tower after extraction and dehydration. The outlet temperature is reduced to 5°C higher than the inlet temperature of the low-temperature VCM. In the third step, the product is mixed and cooled twice, enters the extraction tower II and is fully mixed with the low-temperature extract sent by the extraction liquid circulation pump, then enters the cooler, and undergoes indirect heat exchange with the low-temperature brine to a temperature of -5 to -20°C, and then enters the extraction tower III; The fourth step is extraction and dehydration. After staying in extraction tower III for a sufficient period of time, the monomer overflows from the top of extraction tower III and enters the separation tower to further remove residual water. It then enters the heat exchanger to reuse cooling capacity to reduce energy consumption. Finally, it passes through the vinyl chloride monomer circulation pump, boosts the pressure to above 1.2 MPa, and is sent to the downstream distillation system. The extracting liquid described in the above steps is sodium hydroxide solution.

4. The dehydration method according to claim 3, characterized in that The density of the extract is 1.20-1.25 kg / m 3 , the flow meter on the extraction liquid outlet pipe Ⅰ controls 2 to 5 m 3 / h; the online density meter control value on the low concentration extract recovery pipe is 1.20~1.25Kg / m 3 .

5. The dehydration method according to claim 3, characterized in that The water content of vinyl chloride monomer after dehydration is ≤200ppm.

6. The dehydration method according to claim 3, characterized in that The remote control value of the pressure of the extraction tower III is 0.1 to 0.5 MPa, the control value of the vinyl chloride monomer liquid level meter is 8 to 9 m, the control value of the extract liquid level meter is 3 to 4 m, and the control value of the vinyl chloride monomer thermometer is -5 to -20°C.

7. The dehydration method according to claim 3, characterized in that The inlet pipe of the extraction tower I after the pressure reducing valve is provided with an interlocking closing shut-off valve when the pressure is greater than or equal to 0.65 MPa.

8. The dehydration method according to claim 3, characterized in that The brine temperature is -32 to -35°C, and the brine is calcium chloride brine.

Images