Latex defoaming system and method in the production process of special polyvinyl chloride resin

Abstract

The present invention relates to a defoaming system and method in the production process of polyvinyl chloride, especially the defoaming system and method for latex in the production process of special resin for polyvinyl chloride, and relates to the technical field of chemical production. The latex defoaming system involved in the present invention mainly includes a polymerization kettle, a discharge tank, a liquid separator, a vacuum tank, a vacuum degassing and demisting device, a mechanical defoaming unit, a defoaming agent pipeline, a defoaming water pipeline, a water pipe, a foam probe, etc., which are connected in sequence. By adopting the combined method of mechanical defoaming and chemical defoaming, through DCS control, the foam height is monitored in real time, and the addition of defoaming agent, defoaming water and high-pressure water is controlled according to the foam height. Through the present invention, the effect of not adding chemical defoaming agent to the latex can be basically achieved, reducing the cost and at the same time reducing the impact on the product quality.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical production, and particularly relates to a latex defoaming system and method in the production process of special-purpose polyvinyl chloride resin. Background Art

[0002] Special-purpose polyvinyl chloride resin is a highly dispersed powdery substance with a resin particle size range of 0.1 - 2 μm, having excellent pasting properties and being widely used in many material and product fields. Common production methods of special-purpose polyvinyl chloride resin include emulsion method, micro-suspension method, seed micro-suspension mixing method, etc. In the micro-suspension method, after the polymerization reaction is completed, the material in the kettle becomes latex. Some initiators, emulsifiers, viscosity reducers, fine colloids, etc. will remain in the latex, and foam will be generated during the subsequent treatment process. The traditional defoaming method is to add defoaming agents to the latex, which not only increases the production cost but also affects the stability of the latex and the product performance.

[0003] Some production enterprises use mechanical defoaming or chemical defoaming methods to eliminate the foam generated during the recycling process. The device and production method for producing polyvinyl chloride paste resin by micro-suspension emulsion proposed in the patent with publication number CN105693899A transfers the polymerized material to a discharge tank and uses a defoaming machine to treat the defoaming generated in the discharge tank, but does not describe in detail the structure of the defoaming machine and the defoaming effect, and the operation cost of the device and equipment is relatively high. The patent with publication number CN107141386A proposes a method for producing polyvinyl chloride paste resin and a reaction recycling device. This patent mainly uses a defoaming tower for mechanical defoaming, but there is no device for monitoring the foam situation during the recycling process and cannot accurately judge the defoaming effect of the recycling. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to propose a latex defoaming system and method in the production process of special-purpose polyvinyl chloride resin to solve the above problems.

[0005] For the above purposes, the present invention provides a latex defoaming system in the production process of special polyvinyl chloride resin, including: a polymerization kettle, a discharge tank, a liquid separator, a vacuum tank, a vacuum degassing and demisting device, a mechanical defoaming unit, a defoaming agent pipeline, a defoaming water pipeline, a water pipe, and a foam probe; the discharge port of the polymerization kettle is connected to the feed port of the discharge tank, and the gas outlet of the discharge tank is connected with a liquid separator; the discharge port of the discharge tank is connected to the feed port of the vacuum tank, and the gas outlet of the vacuum tank is connected with a vacuum degassing and demisting device; mechanical defoaming units are respectively connected inside the discharge tank and the vacuum tank; a first defoaming spray head is installed at the top of the liquid separator, a second defoaming spray head and a first spray valve are respectively installed at the top of the discharge tank, a third defoaming spray head and a second spray valve are respectively installed at the top of the vacuum tank, and a fourth defoaming spray head is installed at the top of the vacuum degassing and demisting device; the first defoaming spray head is respectively connected to the defoaming agent pipeline and the defoaming water pipeline, the second defoaming spray head and the third defoaming spray head are respectively connected to the defoaming agent pipeline, the fourth defoaming spray head is connected to the defoaming water pipeline, and the first spray valve and the second spray valve are respectively connected to the water pipe; foam probes are respectively installed inside the discharge tank, the vacuum tank, and the vacuum degassing and demisting device.

[0006] Further, the system further includes a first pipeline and a first flushing water pipeline, and the gas inlet of the liquid separator is connected to the gas outlet of the discharge tank; the liquid outlet of the liquid separator is connected to one end of the first pipeline, a first sight glass and a first U-shaped bend are respectively installed on the first pipeline, the other end of the first pipeline is connected to the discharge tank; the first flushing water pipeline is connected to the first pipeline.

[0007] Further, the system further includes a second pipeline and a second flushing water pipeline, and the gas inlet of the vacuum degassing and demisting device is connected to the gas outlet of the vacuum tank; the liquid outlet of the vacuum degassing and demisting device is connected to one end of the second pipeline, a second sight glass and a second U-shaped bend are respectively installed on the second pipeline, the other end of the second pipeline is connected to the vacuum tank; the second flushing water pipeline is connected to the second pipeline.

[0008] Further, the mechanical defoaming unit includes a stirring shaft, stirring blades, and defoaming rake teeth. Three layers of stirring blades are sequentially connected to the stirring shaft from bottom to top; the defoaming rake teeth include a sleeve, a cross bar, and a round tube. The sleeve is fixedly sleeved on the stirring shaft, the sleeve is located above the three layers of stirring blades, cross bars are respectively connected to both sides of the sleeve, and uniformly distributed round tubes are connected to the lower surface of the cross bar, and the round tubes are arranged vertically. The mechanical defoaming unit is the defoaming rake teeth. The defoaming is carried out by driving the defoaming rake teeth through the stirring and rotation of the equipment. Compared with using a defoaming machine for defoaming, it does not require additional energy consumption, the device is simple, and there is no operating cost.

[0009] A latex defoaming method in the production process of special polyvinyl chloride resin is carried out according to the following steps:

[0010] S1. Transfer the latex in the polymerization kettle to the discharge tank, and start the mechanical defoaming unit in the discharge tank to stir the material. Obtain the first foam height in the discharge tank through the foam probe in the discharge tank, and calculate the proportion of the first foam height. When the proportion of the first foam height is greater than 2%, start the first defoaming nozzle and connect the defoaming water pipeline to spray defoaming water into the liquid separator. When the proportion of the first foam height is greater than 5%, switch the first defoaming nozzle to connect to the defoaming agent pipeline and spray defoaming agent into the liquid separator. When the proportion of the first foam height is greater than 10%, start the first spray valve and spray high-pressure water into the discharge tank. When the proportion of the first foam height is greater than 30%, start the second defoaming nozzle and spray defoaming agent into the discharge tank.

[0011] S2. Transfer the latex in the discharge tank to the vacuum tank, and start the mechanical defoaming unit in the vacuum tank to stir the material. Obtain the second foam height in the vacuum tank through the foam probe in the vacuum tank, and calculate the proportion of the second foam height. When the proportion of the second foam height is greater than 10%, start the second spray valve and spray high-pressure water into the vacuum tank. When the proportion of the second foam height is greater than 30%, start the third defoaming nozzle and spray defoaming agent into the vacuum tank. Obtain the third foam height in the vacuum degassing and demisting device through the foam probe in the vacuum degassing and demisting device, and calculate the proportion of the third foam height. When the proportion of the third foam height is greater than 10%, start the fourth defoaming nozzle and spray defoaming water into the vacuum degassing and demisting device.

[0012] Further, the defoaming water is industrial water with a water pressure of 0.7 - 1.2 MPa.

[0013] Further, the high-pressure water is industrial water with a water pressure of 2.5 - 4.5 MPa.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: Foam probes are installed in the discharge tank, the vacuum tank, and the vacuum degassing and demisting device, which can monitor the foam situation in the equipment in real time, and spray high-pressure water, defoaming water, or defoaming agent into the recovery equipment for defoaming according to the foam situation in the equipment. During the normal recovery process, almost no defoaming agent needs to be sprayed into the equipment to eliminate foam, which reduces costs and has less impact on product quality. Combined with mechanical defoaming, the defoaming effect is remarkable, and the foam height in the main recovery equipment is basically maintained below 10%. Description of the Drawings

[0015] Figure 1 It is a schematic diagram of the latex defoaming system during the production process of the special resin for polyvinyl chloride provided by the embodiment of the present invention;

[0016] Figure 2 It is a schematic diagram of the mechanical defoaming unit of the latex defoaming system during the production process of the special resin for polyvinyl chloride provided by the embodiment of the present invention;

[0017] Figure 3 Schematic diagram of the first pipeline of the latex defoaming system in the production process of the special resin for polyvinyl chloride provided by the embodiment of the present invention;

[0018] Figure 4 Schematic diagram of the second pipeline of the latex defoaming system in the production process of the special resin for polyvinyl chloride provided by the embodiment of the present invention.

[0019] In the figure, the markings are: 1, polymerization kettle; 2, discharge tank; 3, liquid separator; 4, vacuum tank; 5, vacuum degassing and demisting device; 6, discharge pump; 7, transfer pump; 8, stirring shaft; 9, defoaming rake teeth; 10, stirring blade; 11, first pipeline; 12, first flushing water pipeline; 13, first U-shaped bend; 14, second pipeline; 15, second flushing water pipeline; 16, second U-shaped bend. Specific embodiments

[0020] In order to make the purpose, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments.

[0021] As Figures 1 to 4 shown, a latex defoaming system in the production process of a special resin for polyvinyl chloride proposed by the present invention is composed of a polymerization kettle 1, a discharge tank 2, a liquid separator 3, a vacuum tank 4, a vacuum degassing and demisting device 5, a mechanical defoaming unit, etc. A discharge port is provided at the bottom of the polymerization kettle 1. One end of the discharge port of the polymerization kettle 1 is connected to one end of the discharge pump 6. The discharge tank 2 is of a cylindrical barrel structure. In this embodiment, a discharge port is provided at the upper part of the discharge tank 2, an air outlet is provided at the top, and a discharge port is provided at the bottom. The feed port of the discharge tank 2 is connected to the other end of the discharge pump 6. The feed port of the discharge tank 2 is a long pipe insertion type, avoiding some materials in the pipeline during the discharging process from being carried into the liquid separator 3 by gas before they have time to fall.

[0022] The air inlet of the liquid separator 3 is connected to the air outlet of the discharge tank 2. The liquid droplets are separated by the liquid separator 3. The liquid outlet of the liquid separator 3 is connected to one end of the first pipeline 11. A first sight glass and a first U-shaped bend 13 are respectively installed on the first pipeline 11. The other end of the first pipeline 11 is connected to the top of the discharge tank 2. The liquid droplets separated by the liquid separator 3 are returned to the discharge tank 2, and a liquid seal is formed at the first U-shaped bend 13 to prevent the gas in the discharge tank 2 from entering from the bottom of the first pipeline 11 through the first pipeline 11 and affecting the gas-liquid separation effect. The first flushing water pipeline 12 is connected to the first pipeline 11. After the discharge tank 2 finishes recycling, the first pipeline 11 is flushed by using the first flushing water pipeline 12 to prevent the accumulation of latex droplets at the first U-shaped bend 13 and cause blockage of the first pipeline 11.

[0023] The discharge port of the discharge chute 2 is connected to one end of the transfer pump 7, and the other end of the transfer pump 7 is connected to the feed port of the vacuum tank 4. The vacuum tank 4 is of a cylindrical barrel structure. In this embodiment, the upper part of the vacuum tank 4 is provided with a feed port, the top is provided with an air outlet, and the bottom is provided with a discharge port. The feed port of the vacuum tank 4 is of a long pipe insertion type to prevent some of the materials in the pipeline from being carried into the vacuum degassing and demisting device 5 by the gas before they have time to fall during the discharging process.

[0024] The air inlet of the vacuum degassing and demisting device 5 is connected to the air outlet of the vacuum tank 4. The air inlet of the vacuum degassing and demisting device 5 enters tangentially, and the latex droplets in the gas are separated by a rotating separation method.

[0025] The liquid outlet of the vacuum degassing and demisting device 5 is connected to one end of the second pipeline 14. A second sight glass and a second U-shaped bend 16 are respectively installed on the second pipeline 14. The other end of the second pipeline 14 is connected to the top of the vacuum tank 4. The separated latex droplets in the gas phase return to the vacuum tank 4 and form a liquid seal at the second U-shaped bend 16 to prevent the gas in the vacuum tank 4 from entering the bottom of the vacuum degassing and demisting device 5 through the second pipeline 14 and affecting the gas-liquid separation effect. The second flushing water pipeline 15 is connected to the second pipeline 14. After the recovery of the vacuum tank 4, the second pipeline 14 is flushed by using the second flushing water pipeline 15 to prevent the accumulation of latex droplets at the second U-shaped bend 16 and cause blockage of the second pipeline 14.

[0026] Mechanical defoaming units are respectively connected inside the discharge chute 2 and the vacuum tank 4. The mechanical defoaming unit is composed of a stirring shaft 8, stirring blades 10 and defoaming rake teeth 9. Three layers of stirring blades 10 are sequentially connected to the stirring shaft 8 from bottom to top, and the three layers of stirring blades 10 are arranged in the middle position of the tank body. The defoaming rake teeth 9 are composed of a sleeve, a cross bar and a round tube. The sleeve is fixedly sleeved on the stirring shaft 8. The sleeve is located above the three layers of stirring blades 10. Cross bars are respectively connected to both sides of the sleeve, and evenly distributed round tubes are connected to the lower surface of the cross bar. The round tubes are arranged vertically. The defoaming rake teeth 9 rotate with the stirring shaft 8 to eliminate some foams in the form of mechanical defoaming.

[0027] The first defoaming spray head is installed on the top of the liquid separator 3. The second defoaming spray head and the first spray valve are respectively installed on the top of the discharge chute 2. The third defoaming spray head and the second spray valve are respectively installed on the top of the vacuum tank 4. The fourth defoaming spray head is installed on the top of the vacuum degassing and demisting device 5. The first defoaming spray head is respectively connected to the defoaming agent pipeline and the defoaming water pipeline. A chemical defoaming agent is introduced into the defoaming agent pipeline, and industrial water is introduced into the defoaming water pipeline. The second defoaming spray head and the third defoaming spray head are respectively connected to the defoaming agent pipeline, and the fourth defoaming spray head is connected to the defoaming water pipeline. The first spray valve and the second spray valve are respectively connected to the water pipe, and high-pressure water is introduced into the water pipe. Foam probes are respectively installed inside the discharge chute 2, the vacuum tank 4 and the vacuum degassing and demisting device 5.

[0028] Method for defoaming latex in the production process of special polyvinyl chloride resin. The recovery process can adopt manual, PLC or DCS control methods, etc., and is carried out according to the following steps:

[0029] S1. Transfer the latex in the polymerization kettle 1 to the discharge tank 2, and start the mechanical defoaming unit in the discharge tank 2 to stir the material. Under the action of the shearing force of the stirring, foam will be generated in the latex. On the one hand, mechanical defoaming is carried out under the action of the defoaming rake teeth 9; on the other hand, the foam height in the discharge tank 2 is controlled by the auxiliary agent defoaming unit. Obtain the first foam height in the discharge tank 2 through the foam probe in the discharge tank 2, calculate the first foam height ratio, and the first foam height ratio = [first foam height / (height of the discharge tank 2 - height of the latex medium in the discharge tank 2)] × 100%. When the first foam height ratio is greater than 2%, start the first defoaming spray head and connect to the defoaming water pipeline to spray defoaming water into the liquid separator 3; when the first foam height ratio is greater than 5%, turn the first defoaming spray head to connect to the defoaming agent pipeline to spray defoaming agent into the liquid separator 3; when the first foam height ratio is greater than 10%, start the first spray valve to spray water into the discharge tank 2; when the first foam height ratio is greater than 30%, start the second defoaming spray head to spray defoaming agent into the discharge tank 2.

[0030] Correspondingly, until the first foam height ratio drops to less than or equal to 30%, close the second defoaming spray head; when the first foam height ratio is less than or equal to 10%, close the first spray valve; when the first foam height ratio is less than or equal to 5%, turn the first defoaming spray head to connect to the defoaming water pipeline to spray defoaming water into the liquid separator 3; when the first foam height ratio is less than or equal to 2%, close the first defoaming spray head.

[0031] S2. Transfer the latex in the discharge tank 2 to the vacuum tank, and start the mechanical defoaming unit in the vacuum tank 4 to stir the material to accelerate the precipitation of vinyl chloride. However, under the action of the shearing force of the stirring, foam will be generated in the latex. On the one hand, mechanical defoaming is carried out under the action of the defoaming rake teeth 9; on the other hand, the foam heights in the vacuum tank 4 and the vacuum degassing and demisting device 5 are controlled by the auxiliary agent defoaming unit.

[0032] The second foam height in the vacuum tank 4 is obtained through the foam probe in the vacuum tank 4, and the third foam height in the vacuum degassing and defogging device 5 is obtained through the foam probe in the vacuum degassing and defogging device 5. The proportion of the second foam height and the proportion of the third foam height are calculated respectively based on the second foam height and the third foam height. Proportion of the second foam height = [Second foam height / (Height of the vacuum tank 4 - Height of the latex medium in the vacuum tank 4)] × 100%. When the proportion of the second foam height is greater than 10%, the second spray valve is started to spray water into the vacuum tank 4; when the proportion of the second foam height is greater than 30%, the third defoaming nozzle is started to spray defoaming agent into the vacuum tank 4. Correspondingly, until the proportion of the second foam height drops to less than or equal to 30%, the third defoaming nozzle is closed; when the proportion of the second foam height is less than or equal to 10%, the second spray valve is closed.

[0033] Proportion of the third foam height = [Third foam height / (Height of the vacuum degassing and defogging device 5 - Height of the latex medium in the vacuum degassing and defogging device 5)] × 100%. When the proportion of the third foam height is greater than 10%, the fourth defoaming nozzle is started to spray defoaming water into the vacuum degassing and defogging device 5 until the proportion of the third foam height is less than or equal to 10% and then it is closed.

[0034] A method combining mechanical defoaming and chemical defoaming is adopted to eliminate foam. The defoaming rake teeth 9 rotate along with the stirring shaft 8, and part of the foam is eliminated in the form of mechanical defoaming. The height of the foam is detected in real time through the foam probe, and the corresponding defoaming nozzle or spray valve is opened according to the foam proportion, and defoaming is carried out through defoaming water, high-pressure water and defoaming agent. With the combined use of the defoaming rake teeth 9, defoaming water and high-pressure water, it is basically possible to achieve not using defoaming agent, reducing costs while reducing the impact on product quality.

[0035] The following describes this method in combination with specific embodiments.

[0036] Example 1:

[0037] The reaction in this example is carried out in the polymerization kettle 1, and the whole production process is controlled by DCS and carried out according to the following steps.

[0038] a. After the polymerization kettle 1 terminates the reaction, the materials in the kettle are transferred to the discharge tank 2, and the foam height in the discharge tank 2 is controlled through the mechanical defoaming and auxiliary agent defoaming unit to eliminate the foam in the latex. The foam and defoaming actions in the discharge tank 2 are shown in Table 1.

[0039] Table 1 Foam situation in the discharge tank 2 in Example 1

[0040]

[0041] b. Transfer the materials in the discharge tank 2 to the vacuum tank 4, and control the foam height in the vacuum tank 4 and the vacuum degassing and demisting device 5 through the auxiliary agent defoaming unit to reduce the foam in the vacuum tank 4. The foam and defoaming actions in the vacuum tank 4 are shown in Tables 2 and 3 below.

[0042] Table 2 Foam situation in the vacuum tank 4 during the negative pressure recovery process in Example 1

[0043]

[0044] Table 3 Foam situation in the vacuum degassing and demisting device 5 during the negative pressure recovery process in Example 1

[0045]

[0046] Example 2:

[0047] The reaction in this example is carried out in the polymerization kettle 1, and the whole production process is controlled by DCS and carried out according to the following steps.

[0048] a. After the polymerization kettle 1 terminates the reaction, transfer the materials in the kettle to the discharge tank 2, and control the foam height in the discharge tank 2 through the mechanical defoaming and auxiliary agent defoaming units to eliminate the foam in the latex. The foam and defoaming actions in the discharge tank 2 are shown in Table 4.

[0049] Table 4 Foam situation in the discharge tank 2 during the self-pressure recovery process in Example 2

[0050]

[0051] b. Transfer the materials in the discharge tank 2 to the vacuum tank 4, and control the foam height in the vacuum tank 4 and the vacuum degassing and demisting device 5 through the auxiliary agent defoaming unit to reduce the foam in the vacuum tank 4. The foam and defoaming actions in the vacuum tank 4 are shown in Tables 2 and 3 below.

[0052] Table 5 Foam situation in the vacuum tank 4 during the negative pressure recovery process in Example 2

[0053]

[0054] Table 6 Foam situation in the vacuum degassing and demisting device 5 during the negative pressure recovery process in Example 2

[0055]

[0056] The embodiments of the present invention are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for defoaming latex during the production of special polyvinyl chloride resin, characterized in that, Proceed as follows: S1. Transfer the latex in the polymerization kettle to the discharge tank, and start the mechanical defoaming unit in the discharge tank to stir the material; obtain the first foam height in the discharge tank through the foam probe in the discharge tank, and calculate the proportion of the first foam height; when the proportion of the first foam height is greater than 2%, start the first defoaming nozzle and connect the defoaming water pipeline, and spray defoaming water into the liquid separator; when the proportion of the first foam height is greater than 5%, turn the first defoaming nozzle to connect to the defoaming agent pipeline, and spray defoaming agent into the liquid separator; when the proportion of the first foam height is greater than 10%, start the first spray valve and spray high-pressure water into the discharge tank; when the proportion of the first foam height is greater than 30%, start the second defoaming nozzle and spray defoaming agent into the discharge tank; S2. Transfer the latex in the discharge tank to the vacuum tank, and start the mechanical defoaming unit in the vacuum tank to stir the material; obtain the second foam height in the vacuum tank through the foam probe in the vacuum tank, and calculate the proportion of the second foam height; when the proportion of the second foam height is greater than 10%, start the second spray valve and spray high-pressure water into the vacuum tank; when the proportion of the second foam height is greater than 30%, start the third defoaming nozzle and spray defoaming agent into the vacuum tank; Obtain the third foam height in the vacuum degassing and demisting device through the foam probe in the vacuum degassing and demisting device, and calculate the proportion of the third foam height; when the proportion of the third foam height is greater than 10%, start the fourth defoaming nozzle and spray defoaming water into the vacuum degassing and demisting device; The defoaming system used in this defoaming method includes: a polymerization kettle, a discharge tank, a liquid separator, a vacuum tank, a vacuum degassing and demisting device, a mechanical defoaming unit, a defoaming agent pipeline, a defoaming water pipeline, a water pipe and a foam probe; The discharge port of the polymerization kettle is connected to the feed port of the discharge tank, and the gas outlet of the discharge tank is connected with a liquid separator; the discharge port of the discharge tank is connected to the feed port of the vacuum tank, and the gas outlet of the vacuum tank is connected with a vacuum degassing and demisting device; mechanical defoaming units are respectively connected in the discharge tank and the vacuum tank; a first defoaming nozzle is installed at the top of the liquid separator, a second defoaming nozzle and a first spray valve are respectively installed at the top of the discharge tank, a third defoaming nozzle and a second spray valve are respectively installed at the top of the vacuum tank, and a fourth defoaming nozzle is installed at the top of the vacuum degassing and demisting device; the first defoaming nozzle is respectively connected to the defoaming agent pipeline and the defoaming water pipeline, the second defoaming nozzle and the third defoaming nozzle are respectively connected to the defoaming agent pipeline, the fourth defoaming nozzle is connected to the defoaming water pipeline, and the first spray valve and the second spray valve are respectively connected to the water pipe; foam probes are respectively installed in the discharge tank, the vacuum tank and the vacuum degassing and demisting device.

2. The method for defoaming latex in the production process of special polyvinyl chloride resin according to claim 1, characterized in that, It also includes a first pipeline and a first flushing water pipeline. The air inlet of the liquid separator is connected to the gas outlet of the discharge tank; the liquid outlet of the liquid separator is connected to one end of the first pipeline. A first sight glass and a first U-shaped bend are respectively installed on the first pipeline, and the other end of the first pipeline is connected to the discharge tank; the first flushing water pipeline is connected to the first pipeline.

3. The latex defoaming method in the production process of the special polyvinyl chloride resin according to claim 1, characterized in that, It further includes a second pipeline and a second flushing water pipeline. The inlet of the vacuum degassing and demisting device is connected to the outlet of the vacuum tank; the liquid outlet of the vacuum degassing and demisting device is connected to one end of the second pipeline. A second sight glass and a second U-shaped bend are respectively installed on the second pipeline. The other end of the second pipeline is connected to the vacuum tank; the second flushing water pipeline is connected to the second pipeline.

4. The method for defoaming latex in the production process of the special polyvinyl chloride resin according to claim 1, characterized in that, The mechanical defoaming unit includes a stirring shaft, stirring blades and defoaming rake teeth. Three layers of stirring blades are sequentially connected to the stirring shaft from bottom to top; the defoaming rake teeth include a sleeve, a cross bar and a round tube. The sleeve is fixedly sleeved on the stirring shaft. The sleeve is located above the three layers of stirring blades. Cross bars are respectively connected to both sides of the sleeve. Uniformly distributed round tubes are connected to the lower surface of the cross bar, and the round tubes are arranged vertically.

5. The method for defoaming latex during the production process of the special-purpose polyvinyl chloride resin according to claim 1, characterized in that, The defoaming water is industrial water, and the water pressure is 0.7~1.2 MPa.

6. The latex defoaming method in the production process of the special polyvinyl chloride resin according to claim 1, characterized in that, The high-pressure water is industrial water, and the water pressure is 2.5~4.5 MPa.

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