An online cleaning system and method for polyvinyl alcohol production equipment

Abstract

This invention provides an online cleaning system and method for polyvinyl alcohol (PVA) production equipment, relating to the field of filter element cleaning technology. The system can clean the PVA casting solution tank and filter elements online. Through switching between a backup casting solution tank and a backup filter, and with an integrated design for online cleaning of the casting solution tank and filter elements, it achieves a fully closed and online operation, helping to reduce labor intensity and the risk of equipment damage. By simplifying the filter element cleaning process, it improves work efficiency. Furthermore, the system and cleaning method provided by this invention improve the utilization rate of cleaning agents and cleaning wastewater.

Description

Technical Field

[0001] This invention relates to the field of filter cleaning technology, and more specifically, to an online cleaning system and method for polyvinyl alcohol production equipment. Background Technology

[0002] Polyvinyl alcohol (PVA) casting solution must undergo precision filtration before being supplied to the casting system to remove minute impurities. The filtration precision is typically 1–10 microns. Filter cartridges are often made of stacked, candle-type, or pleated metal sintering. After a period of use, clogging may occur, leading to a large inlet-outlet pressure difference. The clogging gradually worsens, eventually requiring shutdown for cleaning. For example, with a 3-micron filter cartridge, when the inlet-outlet pressure difference reaches 5 MPa, a spare cartridge needs to be used or the system needs to be shut down for cleaning. Used filter cartridges must be removed and cleaned immediately to prevent the casting solution from solidifying easily upon cooling.

[0003] After shutdown, the conventional cleaning process is relatively complex and cumbersome. It is generally carried out offline cleaning, which includes boiling with deionized water and using ultrasonic, bubbling and vibration methods to enhance the cleaning effect.

[0004] To reduce downtime or frequent filter cartridge disassembly and assembly, the inlet and outlet pressure differential of the filter cartridge is generally set relatively high. Under high pressure differential conditions, gel impurities present in the casting solution can easily pass through the filter cartridge into subsequent processes, ultimately becoming defects in the membrane product.

[0005] For polyvinyl alcohol casting solution storage tanks, once the material inside the tank is completely emptied, it must be cleaned immediately and kept in reserve to receive casting solution from the previous process. For cleaning the casting solution storage tank without shutting down the machine, first switch to the backup casting solution storage tank. After the casting solution storage tank has been emptied, add pure water and cleaning agent directly and stir and clean it at high temperature. The wastewater is then discharged directly.

[0006] Therefore, in the polyvinyl alcohol casting industry, casting solution is generally produced continuously, and the machine is shut down as much as possible unless necessary, so as to minimize production costs and improve production efficiency.

[0007] The following disadvantages exist in the existing polyvinyl alcohol casting liquid tank and filter cleaning process: (1) The filter element has high disassembly and assembly strength, which poses a risk of damage to the filter chamber; (2) The casting liquid is very easy to solidify after cooling, which requires a high disassembly and assembly speed; (3) During the disassembly and assembly process, the filter element is kept at a high temperature, which poses a risk of burns to personnel; (4) Offline disassembly and assembly cleaning is cumbersome and inefficient; (5) The pressure difference between the inlet and outlet of the filter element is large, and gel impurities will enter the downstream process under high pressure difference, becoming defects in the membrane product; (6) The casting liquid storage tank and filter element cleaning require long-term stirring at high temperature to dissolve, which consumes a lot of energy; (7) The wastewater from the casting liquid storage tank cleaning is directly discharged, which has low utilization rate and wastes resources.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide an online cleaning system and method for polyvinyl alcohol production equipment, thereby enabling online cleaning of the casting solution storage tank and the filter element of the casting solution filter; reducing the impact of gel impurities on membrane products and improving the quality of membrane products.

[0010] This invention is implemented as follows: In a first aspect, the present invention provides an online cleaning system for polyvinyl alcohol production equipment, comprising: Main inlet pipe: used to connect to an external clean water source; the main inlet pipe connects to the cleaning water pipe of the casting solution storage tank; Compressed gas main pipe: used to connect to external compressed gas; the compressed gas main pipe connects to the compressed gas pipeline of the casting solution storage tank; Cosolvent main pipe: used to connect external cosolvents; the cosolvent main pipe connects to the cosolvent inlet pipe of the casting solution storage tank; Filter: Includes at least two filter elements; And the main wastewater pipe; The casting solution storage tank is connected to the filter inlet pipe via the discharge pipe. In order to improve the material conveying efficiency, a discharge pump is also installed on the discharge pipe to convey the material to the filter element for filtration. The filter has a discharge pipe for discharging material to subsequent processes. The casting solution storage tank also has a backwashing pipeline. The inlet end of the backwashing pipeline is connected to the outlet pipeline of the casting solution storage tank. The outlet end of the backwashing pipeline has a first branch and a second branch. The first branch is connected to the outlet pipeline of at least one filter element of the filter. A backwashing waste liquid pipe is led out from the inlet pipe of the filter and is connected to the wastewater main pipe. The second branch is connected to the wastewater main pipe, or the second branch is connected to the wastewater main pipe and the second branch is connected to the outlet pipeline of at least one filter element of the filter.

[0011] The first branch is used to guide the waste liquid from the cleaning of the casting solution storage tank and pipeline to the filter element whose differential pressure exceeds the alarm setting value. After rinsing the filter element, the waste liquid is discharged to the main wastewater pipe.

[0012] The second branch is used when performing "non-"backwashing" tasks, to discharge the waste liquid from the cleaned casting solution storage tank and pipelines to the main wastewater pipe. In other embodiments, the second branch can also be used for backwashing one or more filter cartridges, with a bypass provided for external waste liquid discharge.

[0013] In one embodiment, the first branch can have multiple branches for connecting multiple filter elements in one filter, or connecting multiple filter elements in multiple filters. The number of filter elements in the filter includes, but is not limited to, 2, 3, 4, 5-100. Optionally, one filter element is used and one is spared; one filter element is used and two are spared; or multiple filter elements are used and multiple are spared.

[0014] The external compressed gas is preferably compressed air. It serves to clean the tank and pipelines, as well as to backwash the pipelines and filter elements.

[0015] In a preferred embodiment of the present invention, a backwash valve is provided at the outlet end of the first branch and the second branch of the backwash pipeline. In a preferred embodiment of the present invention, the outlet end of the second branch of the backwashing pipeline has one branch for connecting to the outlet pipeline of the filter element, and another branch for connecting to the main wastewater pipeline; the branch for connecting to the outlet pipeline of the filter element is provided with a backwashing valve at the inlet end to control the backwashing liquid to enter the outlet pipeline of the filter element. The first branch of the backwashing pipeline leads from the filter element's outlet pipeline to the backwash waste liquid pipe, which is connected to the main wastewater pipe. A valve is installed at the inlet end of the first branch of the backwashing pipeline. In this pipeline configuration, one branch is used for backwashing one or more filter elements, while another branch, in addition to being used for backwashing one or more filter elements, is also equipped with a bypass for discharging waste liquid.

[0016] In a preferred embodiment of the present invention, a separate branch can be provided specifically for backwashing the filter element, and another branch can be used for bypass discharge of waste liquid. For example, in a preferred embodiment of the present invention, the outlet end of the first branch of the backwash pipeline has multiple branch lines for connecting the outlet pipelines of multiple filter elements, and each branch line leads one or more backwash liquid waste pipes from the outlet pipeline of the filter element; the backwash liquid waste pipes are connected to the main wastewater pipe; Each branch is equipped with a backwash valve at the inlet end to control the backwash liquid entering the outlet pipe of the filter element; A valve is installed at the inlet end of the second branch of the backwash pipeline.

[0017] In a preferred embodiment of the present invention, a control valve is provided on the backwash waste liquid pipe.

[0018] In a preferred embodiment of the present invention, multiple filter elements in the filter are connected in parallel, and multiple branch lines at the outlet end of the first branch are connected in parallel. Pressure gauges are installed at the inlet and outlet ends of the filter element. These gauges are used to indicate the pressure and pressure difference before and after filtration.

[0019] In a preferred embodiment of the present invention, a valve is provided on the cleaning water pipe of the casting liquid storage tank and a valve is provided on the discharge pipe of the casting liquid storage tank. In a preferred embodiment of the present invention, the valve of the discharge pipeline of the casting liquid storage tank is a downward-expanding plunger valve. A three-way valve is installed at the connection between the discharge pipe of the casting solution storage tank and the inlet pipe of the filter, and a three-way valve is also installed on the discharge pipe of the filter. Other valves are preferably pneumatic ball valves.

[0020] In one embodiment, the casting liquid pipeline from the bottom outlet of the casting liquid storage tank to the subsequent section is a steam-jacketed pipe or a steam-insulated tracing pipe.

[0021] In a preferred embodiment of the present invention, a valve is provided on the gas pipeline of the casting liquid storage tank to control the entry of compressed gas into the casting liquid storage tank.

[0022] In a preferred embodiment of the present invention, a valve is provided on the cosolvent feed pipeline to control the cosolvent entering the casting solution storage tank.

[0023] In a preferred embodiment of the present invention, a valve is provided at the inlet end of the backwashing pipeline of each casting solution storage tank.

[0024] Secondly, the present invention also provides a method for online cleaning of polyvinyl alcohol (PVA) production equipment based on an online cleaning system for PVA production equipment, which includes the following steps: When material discharge is completed from any casting solution storage tank and the filter element pressure difference has not reached the preset value, the feeding tank of the casting solution storage tank is switched; then water is added to the casting solution storage tank after discharge from the main water inlet pipe; cosolvent is added to the casting solution storage tank from the main cosolvent pipe through the cosolvent feed pipe; then stirring is performed to raise the temperature of the casting solution storage tank to the preset temperature; after stirring and cleaning, the cleaning wastewater is discharged to the wastewater main pipe through the discharge pipe and the second branch of the backwash pipe; then the valve of the compressed gas pipe of the casting solution storage tank is opened to allow external compressed gas to enter the casting solution storage tank through the compressed gas main pipe and compressed gas pipe to purge the casting solution storage tank and pipeline; When the filter element pressure difference reaches a preset value during the material discharge process in any casting liquid storage tank, the filter element is switched to another standby filter element; the discharge of the original filter element to the subsequent process is shut off. After the filter element is switched, maintain the temperature of the filter element; after the material discharge from the casting liquid storage tank is completed, switch the feeding tank of the casting liquid storage tank. Then, the casting solution storage tank after discharge is cleaned, and the filter element whose pressure difference reaches the preset value is backwashed. The process includes the following steps: adding water to the casting solution storage tank after discharge, and adding co-solvent to the casting solution storage tank through the co-solvent inlet pipe from the co-solvent main pipe; then stirring to raise the temperature of the casting solution storage tank to the preset temperature; after stirring and cleaning, opening the valves of the compressed gas pipeline, the first branch of the backwash pipeline, and the backwash waste liquid pipeline of the casting solution storage tank; allowing external compressed gas to enter the casting solution storage tank through the compressed gas main pipe and compressed gas pipeline, using the cleaning wastewater in the casting solution storage tank to backwash the filter element, and discharging the wastewater through the first branch to the wastewater main pipe; after the wastewater is discharged, the casting solution storage tank and pipeline are purged again with compressed gas.

[0025] The preset value for filter element differential pressure refers to a value that triggers an alarm when the filter element differential pressure indicator reaches the set value. When the differential pressure indicator of a specific filter element in the filter reaches the set value, an alarm is triggered, and the system can switch to a standby filter element online. The alarm value for filter element differential pressure can be set as needed, such as 3.0 MPa - 4.0 MPa.

[0026] In a preferred embodiment of the present invention, the co-solvent is selected from one or more of diethylene glycol, triethylene glycol, and glycerin, and the amount of co-solvent added is 0.05%-5% of the amount of pure water added to the cleaning tank; the temperature inside the casting solution storage tank during stirring and cleaning is 110-160℃.

[0027] The core mechanism by which cosolvents lower the dissolution temperature of polyvinyl alcohol (PVA) lies in their role as plasticizers. They disrupt the strong hydrogen bond network between PVA chains through intermolecular forces, thereby reducing the glass transition temperature and crystallinity of the system. This allows PVA to achieve chain segment movement and solvation at lower thermal energies. Cosolvents do not simply change polarity; rather, they soften the PVA matrix at the microstructural level through an internal plasticizing effect, making it easier for water or other solvents to wet and swell, ultimately achieving rapid dissolution at low temperatures.

[0028] Therefore, the addition of co-solvents can reduce the tank cleaning temperature and stirring time of the casting solution storage tank. The shortened stirring time helps to improve work efficiency and significantly shortens the cleaning time of the casting solution storage tank.

[0029] The amount of co-solvent added is 0.05%-0.1%, 0.05%-1%, or 1%-5% (by mass) of the amount of pure water added to the cleaning tank. Increasing the amount of co-solvent helps to lower the tank cleaning temperature and shorten the tank agitation cleaning time. Different co-solvents have a significant impact on the tank cleaning temperature and cleaning time, but all can maintain the cleanliness of the tank.

[0030] The internal temperature of the casting solution storage tank during stirring and cleaning is, for example, 110-120℃, 110-130℃, or 130℃-160℃.

[0031] Compared with the prior art, the beneficial effects of the present invention are: To overcome the problems of inconvenient filter element cleaning and waste of cleaning fluid in existing technologies, this invention provides an online cleaning system and method for polyvinyl alcohol (PVA) production equipment. This system enables online cleaning of the PVA casting solution tank and filter elements. Through a rational and effective design of the online switching pipelines and online cleaning pipelines for the casting solution tank and filter, it achieves integrated design for switching between backup casting solution tanks and backup filters, and online cleaning of the casting solution tank and filter elements. This allows for a fully closed and online operation, reducing labor intensity and the risk of equipment damage. By simplifying the filter element cleaning process, it improves work efficiency. The system and cleaning method provided by this invention improve the utilization rate of cleaning agents and cleaning wastewater, contributing to resource conservation. By adding a co-solvent, residual PVA in the tank and pipelines can be dissolved in water. Furthermore, the addition of the co-solvent helps reduce the tank cleaning temperature and stirring time. The filter elements can operate under low pressure differential conditions for extended periods, reducing the impact of gel impurities on the membrane product and improving the quality of the membrane product. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the online cleaning system for polyvinyl alcohol production equipment provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the online cleaning system of the existing polyvinyl alcohol production equipment, as shown in Comparative Examples 1-2.

[0034] Icons: 1-First casting solution storage tank; 2-Second casting solution storage tank; 3-First filter element; 4-Second filter element; 5-Filter; 10-First branch; 11-First branch; 12-Second branch; 13-Backwash pipeline; 7-Second branch; 14-Wastewater main; 6-Pressure gauge; 8-Discharge pump; 20-First valve; 21-Second valve; 22-Third valve; 23-Fourth valve; 24-Fifth valve; 25-Sixth valve; 26-Seventh valve; 27-Eighth valve; 28-Ninth valve; 29-Tenth valve; 30-Eleventh valve; 31-Twelfth valve; 32-Thirteenth valve; 33-Fourteenth valve; 34-Fifteenth valve; 35-Sixteenth valve; 36-Seventeenth valve; 37-Eighteenth valve. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0036] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0037] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0038] The terms “first,” “second,” “third,” etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0039] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] Example 1 Please see Figure 1This embodiment provides an online cleaning system for polyvinyl alcohol production equipment, which includes: Main inlet pipe: used to connect to an external purified water source (pure water equipment); the main inlet pipe connects to the cleaning water pipe of the casting solution storage tank; Compressed air main pipe: used to connect to external compressed air; the compressed air main pipe connects to the compressed air pipeline of the casting solution storage tank; Cosolvent main pipe: used to connect to an external cosolvent tank; the cosolvent main pipe connects to the cosolvent inlet pipe of the casting solution storage tank; Filter 5: Includes at least two filter elements; Filter 5 has a jacket that can be heated or insulated with steam; each filter element has an individual pressure gauge indicating the pressure before and after filtration and the differential pressure. When the differential pressure indication of a filter element in Filter 5 reaches a set value, an alarm is triggered, and the filter element can be switched to online as a backup.

[0041] And wastewater main pipe 14; The casting solution storage tank consists of two interchangeable tanks (one for standby). Each tank has a jacket for steam heating or insulation, and the top of the tank has pipes for adding co-solvent, pure water, and compressed air. Once material delivery to one of the casting solution storage tanks is complete, it can be switched online to the standby tank.

[0042] The discharge pipeline is connected to the feed pipeline of filter 5. In order to improve the material conveying efficiency, a discharge pump 8 (i.e., a feed pump) is also installed on the discharge pipeline to pump the casting liquid in the casting liquid storage tank into filter 5 for filtration. Filter 5 has a discharge pipeline for discharging materials to subsequent processes. The casting solution storage tank also has a backwashing pipeline 13. The inlet end of the backwashing pipeline 13 is connected to the outlet pipeline of the casting solution storage tank. A tenth valve 29 is provided at the junction of the inlet end of the backwashing pipeline 13 and the outlet pipeline of the first casting solution storage tank 1. An eleventh valve 30 is provided at the junction of the inlet end of the backwashing pipeline 13 and the outlet pipeline of the second casting solution storage tank 2.

[0043] The backwashing pipeline 13 has a first branch 10 and a second branch 7 at its outlet end. The first branch 10 is connected to the outlet pipeline of the filter 5, and the backwashing waste liquid pipe is led out from the feed pipe of the filter 5. The backwashing waste liquid pipe is connected to the wastewater main pipe 14. The second branch 7 is connected to the wastewater main pipe 14.

[0044] First branch 10: Used to guide the waste liquid from the cleaned casting liquid storage tank and pipeline to the filter element whose differential pressure exceeds the alarm setting value, and after rinsing the filter element, it is discharged to the wastewater main pipe 14.

[0045] Second branch 7: When performing "non" backwashing tasks, the waste liquid from the cleaned casting solution storage tank and pipeline is discharged from this branch to the main wastewater pipe 14.

[0046] In other embodiments, the second branch 7 can also be used for backwashing one or more filter elements, and a bypass is provided for discharging waste liquid. In this embodiment, the second branch 7 includes two branch lines, a first branch line 11 and a second branch line 12. The first branch line 11 is used for backwashing the second filter element 4, and the second branch line 12 is used for discharging waste liquid.

[0047] In this embodiment, filter 5 includes two filter elements, namely a first filter element 3 and a second filter element 4. The first filter element 3 corresponds to the first branch 10, and the second filter element 4 corresponds to the first branch 11 of the second branch 7. One filter element is in use and the other is on standby.

[0048] External compressed air is preferred. It serves to clean the tank and pipelines, as well as to backwash the pipelines and filter elements.

[0049] In a preferred embodiment of the present invention, a backwash valve (twelfth valve 31) is provided at the outlet end of the first branch 10 of the backwash pipeline 13. In a preferred embodiment of the present invention, the outlet end of the first branch 10 of the backwashing pipeline 13 has multiple branch lines for connecting the liquid outlet pipelines of multiple filter elements. Figure 1 As shown, a backwash waste liquid pipe is led out from the outlet pipe of the first filter element 3, and a fifteenth valve 34 is installed on the backwash waste liquid pipe. A backwash waste liquid pipe is led out from the outlet pipe of the second filter element 4, and a sixteenth valve 35 is installed on the backwash waste liquid pipe. The backwash waste liquid pipe is connected to the wastewater main pipe 14.

[0050] Each branch is equipped with a backwash valve at the inlet end to control the backwash liquid entering the outlet pipe of the filter element; specifically, a twelfth valve 31 is provided at the connection between the first branch 11 and the outlet pipe of the first filter element 3, and a thirteenth valve 32 is provided at the connection between the second branch 12 and the outlet pipe of the second filter element 4. The inlet end of the second branch 7 of the backwash pipeline 13 is equipped with a fourteenth valve 33, which is used to discharge the waste liquid from the cleaning tank and pipeline to the main waste liquid pipe.

[0051] In a preferred embodiment of the present invention, a control valve is provided on the backwash waste liquid pipe.

[0052] In a preferred embodiment of the present invention, multiple filter elements in filter 5 are connected in parallel, and multiple branch lines at the outlet end of the first branch 10 are connected in parallel. Pressure gauges 6 are installed at the inlet and outlet ends of the filter element. These gauges are used to indicate the pressure and differential pressure before and after filtration. PT01, PT02, and PDI01 together form the pressure and differential pressure indication for F101A; PT03, PT04, and PDI02 together form the pressure and differential pressure indication for F101B. A fifth valve 24 is installed on the discharge pipe between the first filter element 3 and the second filter element 4, leading to the downstream processing section.

[0053] In a preferred embodiment of the present invention, a sixth valve 25 and a seventh valve 26 are respectively installed on the cleaning water pipes of the first casting liquid storage tank 1 and the second casting liquid storage tank 2. A first valve 20 and a second valve 21 are respectively installed on the discharge pipes of the first casting liquid storage tank 1 and the second casting liquid storage tank 2, respectively, for controlling the material flow out of the first casting liquid storage tank 1 and the second casting liquid storage tank 2. The valves on the discharge pipes of the casting liquid storage tanks are downward-expanding plunger valves.

[0054] A three-way valve, third valve 22, is installed at the junction of the discharge pipeline of the first casting solution storage tank 1 and the discharge pipeline of the second casting solution storage tank 2 to control the switching of the casting solution storage tanks. After the discharge pipelines of the first casting solution storage tank 1 and the second casting solution storage tank 2 merge, the solution is pumped into the inlet pipeline of the filter 5 by the feed pump P101.

[0055] The feed pipe of filter 5 is equipped with a three-way valve fourth valve 23 at the branch node of the feed branch into the first filter element 3 and the feed branch into the second filter element 4, which is used to control the feed from the aforementioned feed pump P101 into the first filter element 3 or the second filter element 4.

[0056] A three-way valve, fifth valve 24, is installed on the discharge pipe of filter 5. This three-way valve is used to control the flow of the membrane liquid filtered by the first filter element 3 on the first branch line 11 or the membrane liquid filtered by the second filter element 4 on the second branch line 12 into the subsequent process section. When the pressure difference between the first filter element 3 and the second filter element 4 reaches the warning value, the five-way valve 24 is controlled to switch the filter element to the subsequent process section.

[0057] Other valves are preferably pneumatic ball valves.

[0058] In one embodiment, the casting liquid pipeline from the bottom outlet of the casting liquid storage tank to the subsequent section is a steam-jacketed pipe or a steam-insulated tracing pipe.

[0059] In a preferred embodiment of the present invention, a seventeenth valve 36 and an eighteenth valve 37 are respectively provided on the gas pipelines of the first casting liquid storage tank 1 and the second casting liquid storage tank 2, for controlling the entry of compressed air into the casting liquid storage tank.

[0060] In a preferred embodiment of the present invention, an eighth valve 27 and a ninth valve 28 are respectively provided on the co-solvent inlet pipelines of the first casting liquid storage tank 1 and the second casting liquid storage tank 2, for controlling the co-solvent entering the casting liquid storage tank.

[0061] In a preferred embodiment of the present invention, a valve is provided at the inlet end of the backwashing pipeline 13 of each casting liquid storage tank.

[0062] Example 2 This embodiment provides an online cleaning method for polyvinyl alcohol production equipment. This embodiment is a method for switching and cleaning the casting liquid storage tank when the pressure difference of filter element 5 does not reach the alarm setting value of 3MPa.

[0063] When the material discharge from the first casting solution storage tank 1 is completed, and the differential pressure PDI01 of the first filter element 3 of the filter 5 used at this time has not reached the alarm setting value of 3MPa, it is only necessary to switch the materials R101 and R102. The steps are as follows: first open the second valve 21, switch the three-way valve 22 to connect R102 to the downstream pipeline, and close the first valve 20. This completes the switching of the casting solution storage tank feeding system, and the second casting solution storage tank 2 will continue to supply material to the subsequent process section through the first filter element 3.

[0064] The number of product defects caused by gel, such as gel points, bubble points, and small holes, in the product film before the switch was detected.

[0065] After the switch is completed, the first casting liquid storage tank 1 must be cleaned immediately. The steps are as follows: (1) Open the sixth valve 25 and add sufficient pure water to R101 and then close it; (2) Open the eighth valve 27 and add diethylene glycol, a cosolvent, in proportion to the amount of pure water to R101 and then close it; (3) Open the stirrer of R101; (4) Open the jacket steam valve and condensate pipeline to raise the temperature inside the R101 tank to 160℃; (5) Stir and clean, and observe whether there is any casting liquid residue on the inner wall of the tank through a test microscope; (6) If there is no residue, open the first valve 20, the tenth valve 29, and the fourteenth valve 33, connect the wastewater discharge pipeline, and discharge the R101 cleaning wastewater to the sewage treatment device; (7) After the wastewater is discharged, close the stirrer, close the steam valve and condensate pipeline, open the seventeenth valve 36 to add compressed air to purge the tank and pipeline until no water vapor is discharged, and then close all valves (first valve 20, seventeenth valve 36, tenth valve 29, and fourteenth valve 33). At this point, the first casting solution storage tank 1 has been cleaned and is ready for use.

[0066] The co-solvent provided in this embodiment is diethylene glycol, and the ratio of co-solvent to water is 0.05%.

[0067] Example 3 This embodiment provides an online cleaning method for polyvinyl alcohol production equipment. In this embodiment, when the pressure difference of filter element 5 reaches the alarm setting value of 3MPa during the discharge process, the filter element is switched. After the discharge of the casting liquid storage tank is completed, the casting liquid storage tank is switched, and the filter element and the casting liquid storage tank are cleaned.

[0068] When the first casting liquid storage tank 1 is discharging material, the pressure difference PDI01 of the first filter element 3 of the filter 5 used has reached the alarm setting value of 3MPa. At this time, the filter element of filter 5 needs to be switched immediately. The steps are as follows: (1) Switch the fifth valve 24 of the three-way valve to close the first filter element 3 to discharge material to the next process section; (2) Switch the fourth valve 23 of the three-way valve to transport the material in R101 to the second filter element 4 through the P101 discharge pump 8. Thus, the switching of the filter element of filter 5 is completed, and the first casting liquid storage tank 1 continues to supply material to the next process section through the second filter element 4.

[0069] The number of product defects caused by gel, such as gel points, bubble points, and small holes, in the product film before the switch was detected.

[0070] After the filter element switching is completed, maintain the temperature of the first filter element 3 to prevent solidification. Once the first casting solution storage tank 1 has completely discharged material through the second filter element 4, it is necessary to switch the R101 and R102 materials. The steps are as follows: first, open the second valve 21; then, switch the three-way valve to the third valve 22 to connect R102 to the downstream pipeline; finally, close the first valve 20. This completes the switching of the casting solution storage tank feeding system, and the second casting solution storage tank 2 will continuously supply material to the subsequent stages through the second filter element 4.

[0071] After the switch is completed, the first casting solution storage tank 1 needs to be cleaned immediately. After cleaning, the F101A is backwashed with the cleaning wastewater. The steps are as follows: (1) Open the sixth valve 25 to add enough pure water to R101 and then close it; (2) Open the eighth valve 27 to add the corresponding proportion of pure water and co-solvent triethylene glycol to R101 and then close it; (3) Turn on the stirrer of R101; (4) Open the jacket steam valve and condensate pipeline to raise the temperature inside R101 to 110℃; (5) Stir and clean, and observe the inner wall of the tank for casting solution residue through a test microscope; (6) If there is no residue, open the seventeenth valve 36 to add compressed air, pressurize R101 to 0.6MPa and then close it. Then open valves 20, 29, 31, and 34 to connect the wastewater backwash F101A discharge pipeline. Use R101 to clean the wastewater backwash F101A and discharge the wastewater to the sewage treatment device. (7) After the wastewater discharge is completed, turn off the agitator, close the steam valve and condensate pipeline, open valve 36 to add compressed air to purge the tank, filter element and pipeline until no water vapor is discharged, and then close all valves (valve 20, 29, 31, and 34). At this point, the first casting liquid storage tank 1 and the first filter element 3 have been cleaned and are ready for use.

[0072] The cosolvent provided in this embodiment is triethylene glycol, and the ratio of cosolvent to water is 5%.

[0073] Example 4 This embodiment provides an online cleaning method for polyvinyl alcohol production equipment. In this embodiment, when the pressure difference of filter element 5 reaches the alarm setting value of 3MPa during the discharge process, the filter element is switched. After the discharge of the casting liquid storage tank is completed, the casting liquid storage tank is switched, and the filter element and the casting liquid storage tank are cleaned.

[0074] When the first casting liquid storage tank 1 is discharging material, the pressure difference PDI01 of the first filter element 3 of the filter 5 used has reached the alarm setting value of 3MPa. At this time, the filter element of filter 5 needs to be switched immediately. The steps are as follows: (1) Switch the fifth valve 24 of the three-way valve to close the first filter element 3 to discharge material to the next process section; (2) Switch the fourth valve 23 of the three-way valve to transport the material in R101 to the second filter element 4 through the P101 discharge pump 8. Thus, the switching of the filter element of filter 5 is completed, and the first casting liquid storage tank 1 continues to supply material to the next process section through the second filter element 4.

[0075] The number of product defects caused by gel, such as gel points, bubble points, and small holes, in the product film before the switch was detected.

[0076] After the filter element switching is completed, maintain the temperature of the first filter element 3 to prevent solidification. Once the first casting solution storage tank 1 has completely discharged material through the second filter element 4, it is necessary to switch the R101 and R102 materials. The steps are as follows: first, open the second valve 21; then, switch the three-way valve to the third valve 22 to connect R102 to the downstream pipeline; finally, close the first valve 20. This completes the switching of the casting solution storage tank feeding system, and the second casting solution storage tank 2 will continuously supply material to the subsequent stages through the second filter element 4.

[0077] After the switch is completed, the first casting solution storage tank 1 needs to be cleaned immediately. After cleaning, the F101A is backwashed with the cleaning wastewater. The steps are as follows: (1) Open the sixth valve 25 and add enough pure water to R101 and then close it; (2) Open the eighth valve 27 and add the corresponding proportion of pure water and cosolvent glycerin to R101 and then close it; (3) Turn on the stirrer of R101; (4) Open the jacket steam valve and condensate pipeline to raise the temperature inside R101 to 130℃; (5) Stir and clean, and observe the inner wall of the tank for casting solution residue through the test microscope; (6) If there is no residue, open the seventeenth valve 36 to add compressed air, pressurize R101 to 0.6MPa and then close it. Open valves 20, 29, 31, and 34 to connect the wastewater backwash F101A discharge pipeline. Use R101 to clean the wastewater backwash F101A and discharge the wastewater to the sewage treatment device. (7) After the wastewater discharge is completed, turn off the agitator, close the steam valve and condensate pipeline, open valve 36 to add compressed air to purge the tank, filter element and pipeline until no water vapor is discharged, and then close all valves (valve 20, 29, 31, and 34). At this point, the first casting liquid storage tank 1 and the first filter element 3 have been cleaned and are ready for use.

[0078] The cosolvent provided in this embodiment is glycerol, and the ratio of cosolvent to water is 1%.

[0079] Comparative Example 1 Compared with Example 3, the only difference is that... Figure 2 The system shown is used to clean the casting solution storage tank. Using professional disassembly tools, the first filter element 3 is immediately removed and cleaned.

[0080] Comparative Example 2 Compared with Example 3, the only difference is that... Figure 2 The system shown is used to clean the casting solution storage tank. Using professional disassembly tools, the first filter element 3 is immediately removed and cleaned.

[0081] When the first casting liquid storage tank 1 is discharging material, the pressure difference PDI01 of the first filter element 3 of the filter 5 used has reached the alarm setting value of 6MPa. At this time, the filter element of filter 5 is switched immediately. The steps are as follows: (1) Switch the fifth valve 24 of the three-way valve to close the first filter element 3 to the subsequent process; (2) Switch the fourth valve 23 of the three-way valve to transport the material in the first casting liquid storage tank 1 to the second filter element 4 through the discharge pump 8 of P101. Thus, the switching of the filter element of filter 5 is completed, and the first casting liquid storage tank 1 continues to supply material to the subsequent process through the second filter element 4.

[0082] The number of product defects caused by gel, such as gel points, bubble points, and small holes, in the product film before the switch was detected.

[0083] After the filter cartridge is switched, maintain the temperature of the first filter cartridge 3 to prevent solidification. Use professional disassembly tools to immediately remove the first filter cartridge 3, place the filter disc in a deionized water bath and boil it at high temperature, then clean it with ultrasonic assistance.

[0084] Experimental Example 1 The quantity and type of defects in the PVA products prepared in Examples 2-4 and Comparative Examples 1-2 were detected, as were the tank cleaning temperature and the time required for tank agitation and cleaning.

[0085] The results are shown in the table below:

[0086] Comparing Comparative Example 1 and Comparative Example 2, the filter switching pressure of Comparative Example 2 is lower than that of Comparative Example 1, and the number of defects in the final downstream membrane product is significantly lower than that of Comparative Example 1.

[0087] Compared with Comparative Examples 1 and 2, Example 2 showed that the filter cartridge switching pressure was lower than that of Comparative Examples 1 and 2, and the final quantity of downstream membrane products was significantly lower than that of Comparative Examples 1 and 2. In Example 1, after adding the co-solvent, the tank stirring and cleaning time was significantly shorter than that of Comparative Examples 1 and 2.

[0088] The experimental results of Examples 2-4 show that different co-solvents have a significant impact on the tank cleaning temperature and cleaning time, but the tanks can be cleaned in all cases. Increasing the amount of co-solvent added helps to shorten the cleaning time and improve work efficiency.

[0089] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An online cleaning system for polyvinyl alcohol production equipment, characterized in that, It includes: Main inlet pipe: used to connect to an external purified water source; The main water inlet pipe is connected to the cleaning water pipe of the casting solution storage tank; Compressed gas main pipe: used to connect to external compressed gas; the compressed gas main pipe is connected to the compressed gas pipeline of the casting liquid storage tank; Cosolvent main pipe: used to connect external cosolvents; the cosolvent main pipe connects to the cosolvent inlet pipe of the casting solution storage tank; Filter: Includes at least two filter elements; And the main wastewater pipe; The casting solution storage tank is connected to the feed pipe of the filter via a discharge pipe, and the filter has a discharge pipe; The casting solution storage tank also has a backwashing pipeline. The inlet end of the backwashing pipeline is connected to the outlet pipeline of the casting solution storage tank. The outlet end of the backwashing pipeline has a first branch and a second branch. The first branch is connected to the outlet pipeline of at least one filter element of the filter. A backwashing waste liquid pipe is led out from the inlet pipe of the filter and is connected to the wastewater main pipe. The second branch is connected to the wastewater main pipe, or the second branch is connected to the wastewater main pipe and the outlet pipeline of at least one filter element of the filter.

2. The online cleaning system for polyvinyl alcohol production equipment according to claim 1, characterized in that, The outlet ends of the first and second branches of the backwash pipeline are equipped with backwash valves. Preferably, the outlet end of the second branch of the backwashing pipeline has one branch for connecting to the liquid outlet pipeline of the filter element, and another branch for connecting to the main wastewater pipeline; the branch for connecting to the liquid outlet pipeline of the filter element is equipped with a backwashing valve at the inlet end to control the backwashing liquid to enter the liquid outlet pipeline of the filter element. The first branch of the backwashing pipeline leads out the backwashing waste liquid pipe from the outlet pipeline of the filter element and connects to the main wastewater pipe; a valve is provided at the inlet end of the first branch of the backwashing pipeline; Preferably, the outlet end of the first branch of the backwash pipeline has multiple branch lines for connecting the liquid outlet pipelines of multiple filter elements, and each branch line leads one or more backwash liquid waste pipes from the liquid outlet pipeline of the filter element; the backwash liquid waste pipes are connected to the wastewater main pipe; Each branch is equipped with a backwash valve at the inlet end to control the backwash liquid from entering the outlet pipe of the filter element; A valve is installed at the inlet end of the second branch of the backwash pipeline.

3. The online cleaning system for polyvinyl alcohol production equipment according to claim 2, characterized in that, A control valve is installed on the backwash waste liquid pipe.

4. The online cleaning system for polyvinyl alcohol production equipment according to claim 2, characterized in that, Multiple filter elements in the filter are connected in parallel, and multiple branch lines at the outlet end of the first branch are connected in parallel; Pressure gauges are installed at the inlet and outlet ends of the filter element.

5. The online cleaning system for polyvinyl alcohol production equipment according to claim 1, characterized in that, A valve is installed on the cleaning water pipe of the casting solution storage tank, and a valve is installed on the discharge pipe of the casting solution storage tank. Preferably, the valve on the discharge pipeline of the casting liquid storage tank is a bottom-expanding plunger valve; A three-way valve is installed at the connection between the discharge pipe of the casting liquid storage tank and the inlet pipe of the filter, and a three-way valve is installed on the discharge pipe of the filter.

6. The online cleaning system for polyvinyl alcohol production equipment according to claim 1, characterized in that, Valves are installed on the gas pipeline of the casting solution storage tank.

7. The online cleaning system for polyvinyl alcohol production equipment according to claim 1, characterized in that, A valve is installed on the cosolvent feed line.

8. The online cleaning system for polyvinyl alcohol production equipment according to claim 1, characterized in that, Each of the casting solution storage tanks is equipped with a valve at the inlet end of the backwashing pipeline.

9. A method for online cleaning of polyvinyl alcohol production equipment based on the online cleaning system for polyvinyl alcohol production equipment according to any one of claims 1-8, characterized in that, It includes the following steps: When material discharge from any casting solution storage tank is completed and the filter element pressure difference has not reached the preset value, the feeding tank of the casting solution storage tank is switched; then water is added to the casting solution storage tank after discharge from the main water inlet pipe; cosolvent is added to the casting solution storage tank through the cosolvent feed pipe from the main cosolvent pipe; then stirring is performed to raise the temperature of the casting solution storage tank to the preset temperature; after stirring and cleaning, the cleaning wastewater is discharged to the wastewater main pipe through the discharge pipe and the second branch of the backwash pipe; then the valve of the compressed gas pipe of the casting solution storage tank is opened to allow external compressed gas to enter the casting solution storage tank through the compressed gas main pipe and compressed gas pipe to purge the casting solution storage tank and pipeline; When the filter element pressure difference reaches a preset value during the material discharge process in any casting liquid storage tank, the filter element is switched to another standby filter element; the discharge of the original filter element to the subsequent process is shut off. After the filter element is switched, maintain the temperature of the filter element; after the material discharge from the casting liquid storage tank is completed, switch the feeding tank of the casting liquid storage tank. Then, the casting solution storage tank after discharge is cleaned, and the filter element whose pressure difference reaches the preset value is backwashed after cleaning. The process includes the following steps: adding water to the casting solution storage tank after discharge, and adding co-solvent to the casting solution storage tank through the co-solvent inlet pipe from the co-solvent main pipe; then stirring to raise the temperature of the casting solution storage tank to the preset temperature; after stirring and cleaning, opening the valves of the compressed gas pipeline, the first branch of the backwash pipeline, and the backwash waste liquid pipeline of the casting solution storage tank; allowing external compressed gas to enter the casting solution storage tank through the compressed gas main pipe and compressed gas pipeline, using the cleaning wastewater in the casting solution storage tank to backwash the filter element, and discharging the wastewater through the first branch to the wastewater main pipe; After the wastewater is discharged, the casting solution storage tank and pipelines are purged again with compressed gas.

10. The method for online cleaning of polyvinyl alcohol production equipment according to claim 9, characterized in that, The co-solvent is selected from one or more of diethylene glycol, triethylene glycol, and glycerin, and the amount of co-solvent added is 0.05%-5% of the amount of pure water added to the cleaning tank; the temperature inside the casting solution storage tank during stirring and cleaning is 110-160℃.

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