Polyacrylonitrile solution filtering system and online cleaning method thereof

Abstract

The invention provides a polyacrylonitrile solution filtering system and an online cleaning method thereof, and relates to the technical field of polyacrylonitrile-based carbon fiber production, the polyacrylonitrile solution filtering system comprises a first filter and a second filter; the first filter and the second filter are connected in parallel between the feeding pump and the booster pump to form a first flow path through which the polyacrylonitrile solution enters the booster pump from the feeding pump through the first filter and a second flow path through which the polyacrylonitrile solution enters the booster pump from the feeding pump through the second filter. The two filters are used for filtering a polyacrylonitrile solution behind the feeding pump at the same time, and when one filter needs to be cleaned, the filtering function of the filter is closed for cleaning, so that the situation that gel is generated due to material accumulation at a switching valve and a shutdown filter valve can be avoided; and gel at a switching valve and a shut-down filter valve is difficult to clean. And meanwhile, the problem of fault shutdown or pipeline material leakage caused by pressure relief or overpressure of the feeding pipe due to filter switching can be avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of polyacrylonitrile-based carbon fiber production, and particularly relates to a polyacrylonitrile solution filtering system and an online cleaning method thereof. Background Art

[0002] Polyacrylonitrile fiber is the prerequisite for the preparation of high-performance carbon fiber. Polyacrylonitrile fiber is a polyacrylonitrile solution that is transported to a metering pump through a delivery pipeline under the action of a delivery pump. After filtering and metering, it is ejected from a spinneret into a coagulation bath, and coagulated into primary fibers under the action of double diffusion. After washing, hot water drawing, oiling, drying and densification, steam drawing and other processes, it is finally rolled up to prepare polyacrylonitrile fiber. Among them, gels, impurities, etc. can be removed by filtering to ensure the uniformity and spinnability of the polyacrylonitrile solution, and to ensure the production stability of the polyacrylonitrile fiber preparation process and the high quality of the polyacrylonitrile fiber. The existing filtration process mainly includes primary filtration and secondary filtration. The filtration methods include a single filter and a spare filter. The filters include plate and frame filtration, disc filtration, etc. In actual production, it is necessary to regularly replace the filter cloth or filter disc according to the polyacrylonitrile solution and production operation to ensure the filtration effect.

[0003] When using a single filter to replace the filter cloth or clean the filter disc, the plant usually needs to be stopped, resulting in a waste of polyacrylonitrile solution and affecting the production schedule. For this reason, the relevant technology proposes a one-backup and one-use filtering method. For example, on the basis of the existing polymerization stock solution supply system, at least one controllably connected auxiliary flow path and stock liquid tank for filter switching are added. For the stock liquid to be transported in the switched flow path, after the pressure of the switched flow path is adjusted to the target pressure, the first stock liquid tank is switched to the switched flow path to supply liquid to the subsequent metering pump. During this process, pressure fluctuations will not affect the running flow path, thereby ensuring the performance of the polyacrylonitrile fiber.

[0004] For the one-backup-one-use filtering method, when the filter in use needs to be cleaned, the filter must be stopped and switched to the backup filter. However, the following problems exist during the switching process: (1) The switching valve is in a closed state for a long time, and material is easily accumulated at the switching valve (i.e., the polyacrylonitrile solution does not flow for a long time) and gel is generated, resulting in the switching valve not opening smoothly or even difficult to open during switching, which makes it easier for material to accumulate and generate gel. At the same time, the gel generated at the switching valve is difficult to clean thoroughly, thereby affecting the stable operation of the production of polyacrylonitrile fiber (i.e., precursor) and the product quality. (2) When switching, it is easy to cause pressure relief or overpressure in the feed pipe, resulting in a malfunction and shutdown or leakage in the pipeline. Summary of the invention

[0005] Therefore, the present invention provides a polyacrylonitrile solution filtering system and an online cleaning method thereof, which can solve the technical problems in the prior art that gel is easily generated at the switching valve and is difficult to clean.

[0006] In order to solve the above problems, the present invention provides a polyacrylonitrile solution filtering system, comprising a first filter and a second filter; the first filter and the second filter are connected in parallel between a feed pump and a booster pump, forming a first flow path for the polyacrylonitrile solution to enter the booster pump from the feed pump through the first filter, and a second flow path for the polyacrylonitrile solution to enter the booster pump from the feed pump through the second filter;

[0007] The first flow path includes a first feed valve and a first filter outlet valve; wherein the first feed valve is arranged upstream of the first filter; the first filter outlet valve is arranged downstream of the first filter; a first waste liquid treatment component and a first cleaning component are arranged between the first feed valve and the first filter outlet valve;

[0008] The second flow path includes a second supply valve and a second filter outlet valve; wherein the second supply valve is arranged upstream of the second filter; the second filter outlet valve is arranged downstream of the second filter; and a second waste liquid treatment component and a second cleaning component are arranged between the second supply valve and the second filter outlet valve.

[0009] Further, the first waste liquid treatment component includes a first air inlet pipe; one end of the first air inlet pipe is connected to the first flow path, and the other end of the first air inlet pipe is used to introduce nitrogen; preferably, the first air inlet pipe is located downstream of the first filter;

[0010] Preferably, the first waste liquid treatment component also includes a first air return pipe, one end of which is connected to the first flow path, and the other end of the first air return pipe is used to discharge nitrogen; preferably, the first air return pipe is located upstream of the first filter.

[0011] Further, the first cleaning component includes a first liquid inlet pipe; one end of the first liquid inlet pipe is connected to the first flow path, and the other end of the first liquid inlet pipe is used to pass a cleaning agent; preferably, the cleaning agent is dimethyl sulfoxide; preferably, the first liquid inlet pipe is located upstream of the first filter;

[0012] Preferably, the first cleaning component also includes a first liquid return pipe, one end of which is connected to the first flow path, and the other end of which is used to discharge the cleaning agent; preferably, the first liquid return pipe is located downstream of the first filter.

[0013] Further, the second waste liquid treatment component includes a second air inlet pipe; one end of the second air inlet pipe is connected to the second flow path, and the other end of the second air inlet pipe is used to introduce nitrogen; preferably, the second air inlet pipe is located downstream of the second filter;

[0014] Preferably, the second waste liquid treatment component also includes a second air return pipe, one end of which is connected to the second flow path, and the other end of the second air return pipe is used to discharge nitrogen; preferably, the second air return pipe is located upstream of the second filter.

[0015] Further, the second cleaning component includes a second liquid inlet pipe; one end of the second liquid inlet pipe is connected to the second flow path, and the other end of the second liquid inlet pipe is used to pass a cleaning agent; preferably, the cleaning agent is dimethyl sulfoxide; preferably, the second liquid inlet pipe is located upstream of the second filter;

[0016] Preferably, the second cleaning assembly further comprises a second liquid return pipe, one end of which is connected to the second flow path, and the other end of which is used to discharge the cleaning agent; preferably, the second liquid return pipe is located downstream of the second filter.

[0017] Further, a first discharge valve is provided at a position close to the first supply valve on the first flow path, and the first discharge valve is located downstream of the first supply valve; and / or

[0018] A second discharge valve is provided on the second flow path at a position close to the second supply valve, and the second discharge valve is located downstream of the second supply valve.

[0019] Further, a first drain valve is provided at a position close to the first filter outlet valve on the first flow path, and the first drain valve is located upstream of the first filter outlet valve; and / or

[0020] A second drain valve is provided on the second flow path at a position close to the second filter outlet valve, and the second drain valve is located upstream of the second filter outlet valve.

[0021] On the other hand, the present invention provides an online cleaning method for the polyacrylonitrile solution filtration system described in any one of the above items, comprising:

[0022] Turn off the filtering function of the first filter, and clean the first filter and the first flow path online; after the first filter and the first flow path are cleaned, replace the filtering component of the first filter; and then turn on the filtering function of the first filter;

[0023] Turn off the filtering function of the second filter, and clean the second filter and the second flow path online; after the second filter and the second flow path are cleaned, replace the filtering component of the second filter; then turn on the filtering function of the second filter.

[0024] Further, the step of shutting down the filtering function of the first filter includes: when the filtering pressure difference of the first filter meets the first setting condition, closing the first feed valve and the first filter outlet valve to shut down the filtering function of the first filter; preferably, the first setting condition is: initial pressure difference < filtering pressure difference ≤ critical pressure difference; and / or

[0025] The step of shutting down the filtering function of the second filter comprises: when the filtering pressure difference of the second filter meets the second setting condition, closing the second supply valve and the second filtering outlet valve to shut down the filtering function of the second filter; preferably, the second setting condition is: initial pressure difference < filtering pressure difference ≤ critical pressure difference; and / or

[0026] The step of online cleaning the first filter and the first flow path comprises:

[0027] Step 11) controlling the operation of the first waste liquid treatment component to drain the waste polyacrylonitrile solution in the first flow path and the first filter;

[0028] Step 12) controlling the first cleaning component to operate to clean the first flow path and the first filter;

[0029] Step 13) Repeat steps 11) and 12) until the waste liquid discharged from the first flow path is a colorless liquid, and the first flow path is emptied; and / or

[0030] The step of online cleaning the second filter and the second flow path comprises:

[0031] Step 21) controlling the operation of the second waste liquid treatment component to drain the waste polyacrylonitrile solution in the second flow path and the second filter;

[0032] Step 22) controlling the second cleaning component to operate to clean the second flow path and the second filter;

[0033] Step 23) Repeat steps 21) and 22) until the waste liquid discharged from the second flow path is a colorless liquid, and the second flow path is emptied.

[0034] Further, when the first waste liquid treatment component includes a first air inlet pipe, the step 11) includes: controlling the first air inlet pipe to introduce nitrogen into the first flow path to discharge the waste polyacrylonitrile solution in the first flow path and the first filter; until there is no waste polyacrylonitrile solution in the first flow path, stop introducing nitrogen; and / or

[0035] When the first cleaning component includes a first liquid inlet pipe, the step 12) includes: controlling the first liquid inlet pipe to introduce a cleaning agent into the first flow path until the cleaning agent is discharged from the first flow path, controlling the first flow path to be cut off so that the cleaning agent soaks the first flow path and the first filter, and after the soaking time is ≥5h, discharging the waste liquid; and / or

[0036] When the second waste liquid treatment component includes a second air inlet pipe, the step 21) includes: controlling the second air inlet pipe to introduce nitrogen into the second flow path to discharge the waste polyacrylonitrile solution in the second flow path and the second filter; stopping introducing nitrogen until there is no waste polyacrylonitrile solution in the second flow path; and / or

[0037] When the second cleaning component includes a second liquid inlet pipe, the step 22) includes: controlling the second liquid inlet pipe to introduce a cleaning agent into the second flow path until the cleaning agent is discharged from the second flow path, controlling the second flow path to be cut off so that the cleaning agent soaks the second flow path and the second filter, and after the soaking time is ≥5h, discharging the waste liquid; and / or

[0038] When the first flow path is provided with a first discharge valve and a first emptying valve, after replacing the filter assembly of the first filter, the method further includes:

[0039] Opening the first discharge valve and the first emptying valve, and filling the first flow path with the polyacrylonitrile solution through the metering pump and the first discharge valve until the polyacrylonitrile solution discharged from the first emptying valve is free of bubbles and gels, and has uniform viscosity and color; and / or

[0040] When a second discharge valve and a second emptying valve are provided on the second flow path, after replacing the filter assembly of the second filter, the method further includes:

[0041] The second discharge valve and the second emptying valve are opened, and the polyacrylonitrile solution is charged into the second flow path through the metering pump and the second discharge valve until the polyacrylonitrile solution discharged from the second emptying valve is free of bubbles and gels, and has uniform viscosity and color.

[0042] The polyacrylonitrile solution filtering system and online cleaning method provided by the present invention have the following beneficial effects:

[0043] 1. The present invention provides a polyacrylonitrile solution filtering system, comprising a first filter and a second filter; the first filter and the second filter are connected in parallel between a feed pump and a booster pump, forming a first flow path for the polyacrylonitrile solution to enter the booster pump from the feed pump through the first filter, and a second flow path for the polyacrylonitrile solution to enter the booster pump from the feed pump through the second filter; the first flow path and the second flow path are operated simultaneously; based on the above filtering system, the polyacrylonitrile solution after the feed pump is filtered by two filters at the same time, when it is necessary to clean one of the filters, the filtering function of the filter can be turned off through its corresponding feed valve and filter outlet valve, and then the waste polyacrylonitrile solution in the filter and its corresponding flow path can be emptied through its corresponding waste liquid treatment component, and then the filter and its corresponding flow path can be cleaned through the corresponding cleaning component of the filter; then the other filter and its corresponding flow path are cleaned online according to the above method; the polyacrylonitrile solution filtering system of the present application does not need to use a switching valve, so the problem of easy accumulation of material at the switching valve to produce gel and the difficulty of cleaning the gel at the switching valve can be avoided; at the same time, the problem of failure parking or pipeline leakage caused by pressure relief or overpressure of the feed pipe caused by switching the filter can be avoided.

[0044] 2. Furthermore, the waste liquid treatment component of the present invention includes a corresponding air inlet pipe; the air inlet pipe is used to introduce nitrogen; the cleaning component includes a corresponding liquid inlet pipe; the liquid inlet pipe is used to introduce dimethyl sulfoxide; nitrogen is introduced through the air inlet pipe to empty the waste polyacrylonitrile solution in the corresponding flow path and filter, which can avoid the residual polyacrylonitrile from forming gel after the filter is stopped, thereby avoiding increasing the difficulty of cleaning; dimethyl sulfoxide is then introduced through the liquid inlet pipe, and the flow path and filter are soaked with dimethyl sulfoxide. After a period of time, the waste liquid is discharged and the cleaning is completed.

[0045] 3. On the other hand, the present invention provides an online cleaning method for the above-mentioned polyacrylonitrile solution filtration system, which turns off the filtering function of the first filter and performs online cleaning on the first filter and the first flow path; after the first filter and the first flow path are cleaned, the filtering component of the first filter is replaced; then the filtering function of the first filter is turned on; then the filtering function of the second filter is turned off, and the second filter and the second flow path are cleaned online; after the second filter and the second flow path are cleaned, the filtering component of the second filter is replaced; then the filtering function of the second filter is turned on; based on the above-mentioned online cleaning method, the waste polyacrylonitrile solution is discharged through the waste liquid treatment component corresponding to the filter, and then cleaned through the cleaning component, and then the filtering component is replaced, and the filling is switched to complete the online cleaning and switching of the filtration system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0047] Figure 1 This is a schematic diagram of a polyacrylonitrile solution filtration system for the present application;

[0048] The accompanying drawings are marked as follows:

[0049] 1-feeding pipeline, 21-first air return pipe, 22-second air return pipe, 23-first air inlet pipe, 24-second air inlet pipe, 31-first liquid inlet pipe, 32-second liquid inlet pipe, 33-first liquid return pipe, 34-second liquid return pipe, 4-feeding pump, 51-first filter, 52-second filter, 6-boosting pump, 7-metering pump, 8-spinning assembly, P1-first feeding valve, P2-first filter outlet valve, P3-second feeding valve, P4-second filter outlet valve, N1-first nitrogen inlet valve, N2-second nitrogen inlet valve, F1-first discharge valve, F2-first emptying valve, F3-second discharge valve, F4-second emptying valve, M1-first sulfoxide inlet valve, M2-second sulfoxide inlet valve. DETAILED DESCRIPTION

[0050] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0051] In response to the problems existing in the one-backup-one-use filtering method mentioned in the background technology, the present application provides a polyacrylonitrile solution filtering system and an online cleaning method thereof, which completes the online cleaning and switching of the filtering system through nitrogen discharge, sulfoxide immersion, replacement of filter components, and filling switching, and can avoid malfunction shutdown or pipeline leakage caused by pressure relief or overpressure in the feed pipe caused by switching the filter, thereby achieving thorough cleaning of the filter and avoiding residual old material or gel. After switching, the feed liquid is free of bubbles and gel, and the pressure fluctuation during the switching process is small, which does not affect the fiber quality and stable production operation.

[0052] The present invention is described as follows by way of embodiments below:

[0053] Example 1

[0054] On the one hand, if Figure 1As shown, this embodiment provides a polyacrylonitrile solution filtering system, which includes a first filter 51 and a second filter 52. The first filter 51 and the second filter 52 are connected in parallel between the feed pump 4 and the booster pump 6 to form a first flow path for the polyacrylonitrile solution to enter the booster pump 6 from the feed pump 4 through the first filter 51, and a second flow path for the polyacrylonitrile solution to enter the booster pump 6 from the feed pump 4 through the second filter 52; the first flow path and the second flow path operate simultaneously, that is, during normal operation, the first filter 51 and the second filter 52 operate simultaneously to filter the polyacrylonitrile solution;

[0055] The first flow path includes a first supply valve P1 and a first filter outlet valve P2; wherein the first supply valve P1 is arranged upstream of the first filter 51; the first filter outlet valve P2 is arranged downstream of the first filter 51; a first waste liquid treatment component and a first cleaning component are arranged between the first supply valve P1 and the first filter outlet valve P2; the second flow path includes a second supply valve P3 and a second filter outlet valve P4; wherein the second supply valve P3 is arranged upstream of the second filter 52; the second filter outlet valve P4 is arranged downstream of the second filter 52; a second waste liquid treatment component and a second cleaning component are arranged between the second supply valve P3 and the second filter outlet valve P4.

[0056] The polyacrylonitrile solution filtering system provided in this embodiment, when in use, the polyacrylonitrile solution passes through the feed pump 4 on the feed pipeline 1 through the first filter 51 and enters the boosting pump 6, and at the same time passes through the feed pump 4 through the second filter 52 and enters the boosting pump 6, and after passing through the boosting pump 6, the polyacrylonitrile solution enters the spinneret assembly 8 through the metering pump 7; wherein, the two filters are operated simultaneously to filter the polyacrylonitrile solution; when it is necessary to perform online cleaning on one of the filters, the filtering function of the filter is turned off by closing its corresponding feed valve and filter outlet valve (at this time, the other filter is running to filter the polyacrylonitrile solution), and then the filter and the corresponding flow path in the filter are promptly cleaned through the corresponding waste liquid treatment component. The waste polyacrylonitrile solution is discharged to avoid the formation of gel; the filter and its corresponding flow path are cleaned through the cleaning component corresponding to the filter; after cleaning, the filter component of the filter is replaced, and the filter function is turned on after filling; then another filter and its corresponding flow path are cleaned online according to the above method; the polyacrylonitrile solution filtration system of this embodiment does not need to use a switching valve, so it can avoid the problem of material accumulation and gel at the switching valve and the valve corresponding to the out-of-service filter, and the problem of gel at the switching valve and the valve of the out-of-service filter being difficult to clean and the switching valve being stuck and unable to switch normally; at the same time, it can avoid the problem of fault shutdown or pipeline leakage caused by pressure relief or overpressure in the feed pipe caused by switching the filter.

[0057] Preferably, in order to avoid the generation of bubbles when conveying the polyacrylonitrile solution, the feed pipeline located downstream of the filter is generally set at a higher height than the feed pipeline located upstream of the filter.

[0058] Example 2

[0059] Preferably, this embodiment provides a polyacrylonitrile solution filtration system, compared with embodiment 1, Figure 1 As shown, this embodiment further designs the waste liquid treatment component and the cleaning component as follows:

[0060] The first waste liquid treatment component includes a first air inlet pipe 23; one end of the first air inlet pipe 23 is connected to the first flow path, and the other end of the first air inlet pipe 23 is used to introduce nitrogen; the first air inlet pipe 23 is located downstream of the first filter 51; the first cleaning component includes a first liquid inlet pipe 31; one end of the first liquid inlet pipe 31 is connected to the first flow path, and the other end of the first liquid inlet pipe 31 is used to introduce a cleaning agent (preferably dimethyl sulfoxide); the first liquid inlet pipe 31 is located upstream of the first filter 51.

[0061] In addition, the second waste liquid treatment component includes a second air inlet pipe 24; one end of the second air inlet pipe 24 is connected to the second flow path, and the other end of the second air inlet pipe is used to introduce nitrogen; the second air inlet pipe 24 is located downstream of the second filter 52; the second cleaning component includes a second liquid inlet pipe 32; one end of the second liquid inlet pipe 32 is connected to the second flow path, and the other end of the second liquid inlet pipe 32 is used to introduce a cleaning agent (preferably dimethyl sulfoxide); the second liquid inlet pipe 32 is located upstream of the second filter 52.

[0062] Here, the air inlet pipe for introducing nitrogen is arranged downstream of the corresponding filter so as to quickly fill it with nitrogen and blow it in the reverse direction to ensure that the waste polyacrylonitrile solution can be discharged in time and completely; and the liquid inlet pipe for introducing the cleaning agent is arranged upstream of the corresponding filter. Preferably, the cleaning agent is filled into the bottom of the filter and discharged from the downstream of the corresponding filter or the upper part of the filter, or sulfoxide can be discharged from the valve F2 from the downstream of the filter to the upper part, which indicates that the filter and the front and rear pipelines are full of sulfoxide, ensuring the sulfoxide soaking effect, thoroughly cleaning the filter and pipeline, and achieving dead-angle cleaning.

[0063] Example 3

[0064] Preferably, this embodiment provides a polyacrylonitrile solution filtration system, compared with the above embodiment, Figure 1 As shown, this embodiment further designs the waste liquid treatment component and the cleaning component as follows:

[0065] The first waste liquid treatment component also includes a first return air pipe 21, one end of which is connected to the first flow path, and the other end of the first return air pipe 21 is used to discharge nitrogen; the first return air pipe 21 is located upstream of the first filter 51; the first cleaning component also includes a first liquid return pipe 33, one end of which is connected to the first flow path, and the other end of the first liquid return pipe 33 is used to discharge the cleaning agent (preferably dimethyl sulfoxide); the first liquid return pipe 33 is located downstream of the first filter 51.

[0066] The second waste liquid treatment component also includes a second return air pipe 22, one end of which is connected to the second flow path, and the other end of the second return air pipe 22 is used to discharge nitrogen; the second return air pipe 22 is located upstream of the second filter 52; the second cleaning component also includes a second liquid return pipe 34, one end of which is connected to the second flow path, and the other end of the second liquid return pipe 34 is used to discharge the cleaning agent (preferably dimethyl sulfoxide); the second liquid return pipe 34 is located downstream of the second filter 52.

[0067] Example 4

[0068] Preferably, this embodiment provides a polyacrylonitrile solution filtration system, compared with the above embodiment, Figure 1 As shown, this embodiment is further designed as follows:

[0069] A first discharge valve F1 is provided at a position close to the first supply valve P1 on the first flow path, and the first discharge valve F1 is located downstream of the first supply valve P1; a second discharge valve F3 is provided at a position close to the second supply valve P3 on the second flow path, and the second discharge valve F3 is located downstream of the second supply valve P3. Here, nitrogen or waste polyacrylonitrile solution or cleaning agent solution after cleaning can be discharged through the discharge valve.

[0070] In addition, a first drain valve F2 is provided at a position close to the first filter outlet valve P2 on the first flow path, and the first drain valve F2 is located upstream of the first filter outlet valve P2; a second drain valve F4 is provided at a position close to the second filter outlet valve P4 on the second flow path, and the second drain valve F4 is located upstream of the second filter outlet valve P4. Here, when the drain valve discharges the cleaning agent or polyacrylonitrile solution, it proves that the pipeline is full of the cleaning agent or polyacrylonitrile solution, which can ensure that the immersion or filling is complete.

[0071] In the present invention, a first supply valve P1, a first discharge valve F1, a first return air pipe 21, a first liquid inlet pipe 31, a first filter 51, a first liquid return pipe 33, a first air inlet pipe 23, a first emptying valve F2 and a first filter outlet valve P2 are sequentially arranged on the first flow path downstream of the feed pump 4; a second supply valve P3, a second discharge valve F3, a second return air pipe 22, a second liquid inlet pipe 32, a second filter 52, a second liquid return pipe 34, a second air inlet pipe 24, a second emptying valve F4 and a second filter outlet valve P4 are sequentially arranged on the second flow path downstream of the feed pump 4.

[0072] Among them, based on the above settings, the openings of the first discharge valve F1 and the second discharge valve F3 are set downward, and the openings of the first drain valve F2 and the second drain valve F4 are set upward, which can ensure that the nitrogen gas completely discharges the waste polyacrylonitrile solution, the cleaning agent (dimethyl sulfoxide) is quickly filled during the immersion process, and the filling and cleaning processes do not affect the stability of the feed and production operation.

[0073] Example 5

[0074] On the other hand, this embodiment provides an online cleaning method for a polyacrylonitrile solution filtration system. Preferably, the polyacrylonitrile solution filtration system is the polyacrylonitrile solution filtration system described in any one of Embodiments 1-4.

[0075] When the filtration pressure difference of the first filter 51 satisfies: initial pressure difference < filtration pressure difference ≤ critical pressure difference, close the first supply valve P1 and the first filtration outlet valve P2 to close the filtration function of the first filter 51; then perform online cleaning according to the following steps:

[0076] Step 11) Open the nitrogen inlet valve N1 and the first discharge valve F1 on the first inlet pipe 23, introduce nitrogen into the first flow path and the first filter 51, and adjust the nitrogen pressure to 1-4 kg until no waste liquid (waste polyacrylonitrile solution) is discharged from the first discharge valve F1, and then close the nitrogen inlet valve N1 and the first discharge valve F1;

[0077] Step 12) Open the cleaning agent inlet valve M1 and the first drain valve F2 on the first liquid inlet pipe 31, and introduce the cleaning agent into the first flow path and the first filter 51 until waste liquid is discharged from the first drain valve F2, and then close the cleaning agent inlet valve M1 and the first drain valve F2 (i.e., control the first flow path to be cut off); allow the cleaning agent to soak the second flow path and the first filter 51, and after the soaking time is ≥5h, drain the waste liquid;

[0078] Step 13) Repeat steps 11) and 12) 1-3 times until the waste liquid discharged from the first flow path is a colorless liquid, then clean it, and then empty the first flow path and the first filter 51;

[0079] After the first filter 51 and the first flow path are cleaned and the first flow path and the first filter 51 are emptied, the filter assembly of the first filter is replaced (the filter assembly can be a filter cloth or a filter disc, etc.); after the replacement is completed, ensure that other valves on the first flow path are closed, connect the first discharge valve F1 to the feed pipe after the metering pump through a connecting pipeline (which can be a metal pipe), then open the first discharge valve F1 and the first emptying valve F2, and fill the first flow path with polyacrylonitrile solution through the metering pump and the first discharge valve F1 (i.e., fill), until the polyacrylonitrile solution discharged from the first emptying valve F2 is free of bubbles and gels, and its viscosity and color are uniform, stop filling, that is, close the metering pump 7, the first discharge valve F1 and the first emptying valve F2; wherein, because the filling process uses the feed pipe after the metering pump to feed, and the filter system is filled with no bubbles and no gel flowing out before being put into the system, the stability of the feeding system will not be affected throughout the process;

[0080] Finally, slowly open the first feed valve P1 and the first filter outlet valve P2, that is, start the filtering function of the first filter 51; during the opening process, the feed pressure fluctuation is ≤0.5 kg.

[0081] When the filtration pressure difference of the second filter 52 satisfies: initial pressure difference < filtration pressure difference ≤ critical pressure difference, close the second supply valve P3 and the second filtration outlet valve P4 to close the filtration function of the second filter 52; then perform online cleaning according to the above method, specifically, including the following steps:

[0082] Step 21) Open the nitrogen inlet valve and the second discharge valve F3 on the second inlet pipe 24, introduce nitrogen into the second flow path and the second filter 52, and adjust the nitrogen pressure to 1-4 kg until no waste liquid (waste polyacrylonitrile solution) is discharged from the second discharge valve F3, and then close the nitrogen inlet valve and the second discharge valve F3;

[0083] Step 22) Open the cleaning agent inlet valve M2 and the second drain valve F4 on the second liquid inlet pipe 32, and introduce the cleaning agent into the second flow path and the second filter 52 until waste liquid is discharged from the second drain valve F4, and then close the cleaning agent inlet valve M1 and the second drain valve F4 (i.e., control the second flow path to be cut off); allow the cleaning agent to soak the second flow path and the second filter 52, and after the soaking time is ≥5h, drain the waste liquid;

[0084] Step 23) Repeat steps 21) and 22) 1-3 times until the waste liquid discharged from the second flow path is a colorless liquid, then clean it, and then empty the second flow path and the second filter 52;

[0085] After the second filter 52 and the second flow path are cleaned and the second flow path and the second filter 52 are emptied, the filter assembly of the second filter 52 is replaced (the filter assembly can be a filter cloth or a filter disc, etc.); after the replacement is completed, ensure that other valves on the second flow path are closed, connect the second discharge valve F3 to the feed pipe after the metering pump through a connecting pipeline (which can be a metal pipe), and then open the second discharge valve F3 and the second emptying valve F4, and fill the second flow path with polyacrylonitrile solution through the metering pump and the second discharge valve F3 (i.e., fill), until the polyacrylonitrile solution discharged from the second emptying valve F4 is free of bubbles and gels, and its viscosity and color are uniform, stop filling, that is, close the metering pump 7, the second discharge valve F3 and the second emptying valve F4; wherein, because the filling process uses the feed pipe after the metering pump to feed, and the filter system is filled with no bubbles and no gel flowing out before being put into the system, the stability of the feeding system will not be affected throughout the process;

[0086] Finally, slowly open the second feed valve P3 and the second filter outlet valve P4, that is, start the filtering function of the second filter 52; during the opening process, the feed pressure fluctuation is ≤0.5 kg.

[0087] Filling can avoid pipeline pressure relief when the filter is put into use. After filling, the filter and the corresponding flow path are completely filled with polyacrylonitrile solution. When the filter is filled, the valves before and after the filter are opened, and the feed pressure will not fluctuate greatly. In addition, after filling until there are no bubbles and the viscosity and color of the polyacrylonitrile solution are consistent (uniform), it can be put into filtration. The stable operation will not be affected by bubbles, different viscosities, and the presence of gel. Bubbles will cause broken wires, uneven viscosity will affect the quality stability of polyacrylonitrile fibers, and the presence of gel will cause broken wires, broken ends, and roller entanglement.

[0088] Among them, the filtration pressure difference refers to the difference between the pressure after the current filtration and the pressure before the filtration; the initial pressure difference refers to the initial filtration pressure difference of the filter after the filter assembly (disc or filter cloth, filter element, etc.) is newly replaced; the critical pressure difference refers to the pressure difference of the filtration system will increase as the filtration gel or impurities increase after the filtration system runs for a period of time after the filter assembly is replaced. The critical pressure difference refers to the deterioration of the filtration effect, the gel / impurities cannot be effectively filtered, and are brought into the feed pipeline and spinneret assembly, resulting in broken wires or clogging of the spinneret, affecting stable operation. The critical pressure difference is related to the process, polymer liquid, filtration selection, etc. Generally, a pressure gauge is set on the pipeline immediately before and after the filter. The pressure gauge at the feed end of the filter is used to measure the pressure before the filter, and the pressure gauge at the filter outlet is used to measure the pressure after the filtration. The initial pressure difference is the pressure difference before and after the filtration just after the filter assembly is replaced (that is, when the filter assembly is in a relatively clean state), the filtration pressure difference is the pressure difference before and after the filtration (that is, the current pressure difference), and the critical pressure difference is the pressure difference before and after the filtration when the filter assembly is dirty and cannot play a filtering role (that is, the pressure difference that affects stable operation).

[0089] Experimental Examples

[0090] This experimental example is mainly to investigate the polyacrylonitrile solution filtration system described in the above embodiment of the present invention (i.e., Figure 1 The polyacrylonitrile solution filtration system) is cleaned online as follows:

[0091] The initial pressure difference of the first filter 51 is measured to be 0.2MPa, the filtering pressure difference is 0.9MPa, and the critical pressure difference is 1.0MPa, that is, the filtering pressure difference of the first filter 51 satisfies: when the initial pressure difference 0.2MPa<filtering pressure difference 0.9MPa≤critical pressure difference 1.0MPa, close the first feed valve P1 and the first filter outlet valve P2 to close the filtering function of the first filter 51; then perform online cleaning according to the following steps:

[0092] Step 11) Open the nitrogen inlet valve N1 and the first discharge valve F1 on the first inlet pipe 23, introduce nitrogen into the first flow path and the first filter 51, and adjust the nitrogen pressure to 3 kg until no waste liquid (waste polyacrylonitrile solution) is discharged from the first discharge valve F1, and close the nitrogen inlet valve N1 and the first discharge valve F1;

[0093] Step 12) Open the dimethyl sulfoxide inlet valve M1 and the first drain valve F2 on the first liquid inlet pipe 31, and introduce dimethyl sulfoxide into the first flow path and the first filter 51 until waste liquid is discharged from the first drain valve F2, and then close the dimethyl sulfoxide inlet valve M1 and the first drain valve F2 (i.e., control the first flow path to be cut off); allow dimethyl sulfoxide to soak the second flow path and the first filter 51, and after soaking for 10 hours, drain the waste liquid;

[0094] Step 13) Repeat steps 11) and 12) 3 times until the waste liquid discharged from the first flow path is a colorless liquid, then clean it, and then empty the first flow path and the first filter 51;

[0095] After the first filter 51 and the first flow path are cleaned and the first flow path and the first filter 51 are emptied, the filter assembly of the first filter (the filter assembly is a filter cloth) is replaced; after the replacement is completed, ensure that other valves on the first flow path are closed, connect the first discharge valve F1 to the feed pipe after the metering pump through a connecting pipeline (which can be a metal pipe), then open the first discharge valve F1 and the first emptying valve F2, and fill the first flow path with polyacrylonitrile solution through the metering pump and the first discharge valve F1 until the polyacrylonitrile solution discharged from the first emptying valve F2 is free of bubbles and gels, and its viscosity and color are uniform, stop filling, that is, close the metering pump 7, the first discharge valve F1 and the first emptying valve F2; wherein, because the filling process uses the feed pipe after the metering pump to feed, and the filter system is filled with no bubbles and no gel flowing out before being put into the system, the stability of the feed system before the metering pump will not be affected throughout the process;

[0096] Finally, the first feed valve P1 and the first filter outlet valve P2 are slowly opened, that is, the filtering function of the first filter 51 is turned on; during the opening process, the feed pressure fluctuates by 0.2 kg.

[0097] The initial pressure difference of the second filter 52 is measured to be 0.1 MPa, the filtering pressure difference is 0.95 MPa, and the critical pressure difference is 1.1 MPa. That is, when the filtering pressure difference of the second filter 52 satisfies: initial pressure difference 0.1 MPa<filtering pressure difference 0.95 MPa≤critical pressure difference 1.1 MPa, close the second feed valve P3 and the second filter outlet valve P4 to close the filtering function of the second filter 52; then perform online cleaning according to the above method, specifically, including the following steps:

[0098] Step 21) Open the nitrogen inlet valve and the second discharge valve F3 on the second inlet pipe 24, introduce nitrogen into the second flow path and the second filter 52, and adjust the nitrogen pressure to 3 kg until no waste liquid (waste polyacrylonitrile solution) is discharged from the second discharge valve F3, and then close the nitrogen inlet valve and the second discharge valve F3;

[0099] Step 22) Open the dimethyl sulfoxide inlet valve M2 and the second drain valve F4 on the second liquid inlet pipe 32, and introduce dimethyl sulfoxide into the second flow path and the second filter 52 until waste liquid is discharged from the second drain valve F4, and close the dimethyl sulfoxide inlet valve M1 and the second drain valve F4 (i.e., control the second flow path to be cut off); allow dimethyl sulfoxide to soak the second flow path and the second filter 52, and after soaking for 24 hours, drain the waste liquid;

[0100] Step 23) Repeat steps 21) and 22) twice until the waste liquid discharged from the second flow path is a colorless liquid, then clean it, and then empty the second flow path and the second filter 52;

[0101] After the second filter 52 and the second flow path are cleaned and the second flow path and the second filter 52 are emptied, the filter assembly of the second filter 52 (the filter assembly is a filter disc) is replaced; after the replacement is completed, ensure that other valves on the second flow path are closed, connect the second discharge valve F3 to the feed pipe after the metering pump through a connecting pipeline (which can be a metal pipe), and then open the second discharge valve F3 and the second emptying valve F4, and fill the second flow path with polyacrylonitrile solution through the metering pump and the second discharge valve F3 until the polyacrylonitrile solution discharged from the second emptying valve F4 is free of bubbles and gels, and its viscosity and color are uniform, stop filling, that is, close the metering pump 7, the second discharge valve F3 and the second emptying valve F4; wherein, because the filling process uses the feed pipe after the metering pump to feed, and the filter system is filled with no bubbles and no gel flowing out before being put into the system, the stability of the feed system before the metering pump will not be affected throughout the process;

[0102] Finally, the second feed valve P3 and the second filter outlet valve P4 are slowly opened, that is, the filtering function of the second filter 52 is turned on; during the opening process, the feed pressure fluctuates by 0.1 kg.

[0103] It is easy for those skilled in the art to understand that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention. These improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A polyacrylonitrile solution filtration system, characterized in that: The invention comprises a first filter (51) and a second filter (52); the first filter (51) and the second filter (52) are connected in parallel between a feed pump (4) and a booster pump (6), so as to form a first flow path for a polyacrylonitrile solution to flow from the feed pump (4) through the first filter (51) into the booster pump (6), and a second flow path for a polyacrylonitrile solution to flow from the feed pump (4) through the second filter (52) into the booster pump (6); The first flow path comprises a first supply valve (P1) and a first filter outlet valve (P2); wherein the first supply valve (P1) is arranged upstream of the first filter (51); the first filter outlet valve (P2) is arranged downstream of the first filter (51); a first waste liquid treatment component and a first cleaning component are arranged between the first supply valve (P1) and the first filter outlet valve (P2); The second flow path includes a second supply valve (P3) and a second filter outlet valve (P4); wherein the second supply valve (P3) is arranged upstream of the second filter (52); the second filter outlet valve (P4) is arranged downstream of the second filter (52); and a second waste liquid treatment component and a second cleaning component are arranged between the second supply valve (P3) and the second filter outlet valve (P4).

2. The polyacrylonitrile solution filtration system according to claim 1, characterized in that: The first waste liquid treatment component comprises a first air inlet pipe (23); one end of the first air inlet pipe (23) is connected to the first flow path, and the other end of the first air inlet pipe (23) is used to introduce nitrogen; preferably, the first air inlet pipe (23) is located downstream of the first filter (51); Preferably, the first waste liquid treatment component further comprises a first air return pipe (21), one end of the first air return pipe (21) is connected to the first flow path, and the other end of the first air return pipe (21) is used to discharge nitrogen; preferably, the first air return pipe (21) is located upstream of the first filter (51).

3. The polyacrylonitrile solution filtration system according to claim 1, characterized in that: The first cleaning component comprises a first liquid inlet pipe (31); one end of the first liquid inlet pipe (31) is connected to the first flow path, and the other end of the first liquid inlet pipe (31) is used to introduce a cleaning agent; preferably, the cleaning agent is dimethyl sulfoxide; preferably, the first liquid inlet pipe (31) is located upstream of the first filter (51); Preferably, the first cleaning component further comprises a first liquid return pipe (33), one end of the first liquid return pipe (33) is connected to the first flow path, and the other end of the first liquid return pipe (33) is used to discharge the cleaning agent; preferably, the first liquid return pipe (33) is located downstream of the first filter (51).

4. The polyacrylonitrile solution filtration system according to claim 1, characterized in that: The second waste liquid treatment component comprises a second air inlet pipe (24); one end of the second air inlet pipe (24) is connected to the second flow path, and the other end of the second air inlet pipe (24) is used to introduce nitrogen; preferably, the second air inlet pipe (24) is located downstream of the second filter (52); Preferably, the second waste liquid treatment component also includes a second air return pipe (22), one end of the second air return pipe (22) is connected to the second flow path, and the other end of the second air return pipe (22) is used to discharge nitrogen; preferably, the second air return pipe (22) is located upstream of the second filter (52).

5. The polyacrylonitrile solution filtration system according to claim 1, characterized in that: The second cleaning component comprises a second liquid inlet pipe (32); one end of the second liquid inlet pipe (32) is connected to the second flow path, and the other end of the second liquid inlet pipe (32) is used to introduce a cleaning agent; preferably, the cleaning agent is dimethyl sulfoxide; preferably, the second liquid inlet pipe (32) is located upstream of the second filter (52); Preferably, the second cleaning component further comprises a second liquid return pipe (34), one end of the second liquid return pipe (34) is connected to the second flow path, and the other end of the second liquid return pipe (34) is used to discharge the cleaning agent; preferably, the second liquid return pipe (34) is located downstream of the second filter (52).

6. The polyacrylonitrile solution filtration system according to any one of claims 1 to 5, characterized in that: A first discharge valve (F1) is provided on the first flow path at a position close to the first supply valve (P1), and the first discharge valve (F1) is located downstream of the first supply valve (P1); and / or A second discharge valve (F3) is provided on the second flow path at a position close to the second supply valve (P3), and the second discharge valve (F3) is located downstream of the second supply valve (P3).

7. The polyacrylonitrile solution filtration system according to claim 6, characterized in that: A first drain valve (F2) is provided on the first flow path at a position close to the first filter outlet valve (P2), and the first drain valve (F2) is located upstream of the first filter outlet valve (P2); and / or A second drain valve (F4) is provided at a position close to the second filter outlet valve (P4) on the second flow path, and the second drain valve (F4) is located upstream of the second filter outlet valve (P4).

8. An online cleaning method for a polyacrylonitrile solution filtration system according to any one of claims 1 to 7, characterized in that: include: Turning off the filtering function of the first filter (51), and cleaning the first filter (51) and the first flow path online; after the first filter (51) and the first flow path are cleaned, replacing the filtering component of the first filter (51); and then turning on the filtering function of the first filter (51); The filtering function of the second filter (52) is turned off, and the second filter (52) and the second flow path are cleaned online; after the second filter (52) and the second flow path are cleaned, the filtering component of the second filter (52) is replaced; and then the filtering function of the second filter (52) is turned on.

9. The online cleaning method of the polyacrylonitrile solution filtration system according to claim 8, characterized in that: The step of shutting down the filtering function of the first filter (51) comprises: when the filtering pressure difference of the first filter (51) satisfies a first set condition, closing the first supply valve (P1) and the first filtering outlet valve (P2) to shut down the filtering function of the first filter (51); preferably, the first set condition is: initial pressure difference < filtering pressure difference ≤ critical pressure difference; and / or The step of shutting down the filtering function of the second filter (52) comprises: when the filtering pressure difference of the second filter (52) satisfies a second set condition, closing the second supply valve (P3) and the second filtering outlet valve (P4) to shut down the filtering function of the second filter (52); preferably, the second set condition is: initial pressure difference < filtering pressure difference ≤ critical pressure difference; and / or The step of online cleaning the first filter (51) and the first flow path comprises: Step 11) controlling the operation of the first waste liquid treatment component to drain the waste polyacrylonitrile solution in the first flow path and the first filter; Step 12) controlling the first cleaning component to operate to clean the first flow path and the first filter; Step 13) Repeat steps 11) and 12) until the waste liquid discharged from the first flow path is a colorless liquid, and the first flow path is emptied; and / or The step of online cleaning the second filter (52) and the second flow path comprises: Step 21) controlling the operation of the second waste liquid treatment component to drain the waste polyacrylonitrile solution in the second flow path and the second filter; Step 22) controlling the second cleaning component to operate to clean the second flow path and the second filter; Step 23) Repeat steps 21) and 22) until the waste liquid discharged from the second flow path is a colorless liquid, and the second flow path is emptied.

10. The online cleaning method of the polyacrylonitrile solution filtration system according to claim 9, characterized in that: When the first waste liquid treatment component includes a first air inlet pipe (23), the step 11) includes: controlling the first air inlet pipe (23) to introduce nitrogen into the first flow path to discharge the waste polyacrylonitrile solution in the first flow path and the first filter (51); stopping the introduction of nitrogen until there is no waste polyacrylonitrile solution in the first flow path; and / or When the first cleaning component includes a first liquid inlet pipe (31), the step 12) includes: controlling the first liquid inlet pipe (31) to introduce a cleaning agent into the first flow path until the cleaning agent is discharged from the first flow path, controlling the first flow path to be cut off so that the cleaning agent soaks the first flow path and the first filter, and after the soaking time is ≥5 hours, discharging the waste liquid; and / or When the second waste liquid treatment component includes a second air inlet pipe (24), the step 21) includes: controlling the second air inlet pipe (24) to introduce nitrogen into the second flow path to discharge the waste polyacrylonitrile solution in the second flow path and the second filter (52); stopping the introduction of nitrogen until there is no waste polyacrylonitrile solution in the second flow path; and / or When the second cleaning component includes a second liquid inlet pipe (32), the step 22) includes: controlling the second liquid inlet pipe (32) to introduce a cleaning agent into the second flow path until the cleaning agent is discharged from the second flow path, controlling the second flow path to be cut off so that the cleaning agent soaks the second flow path and the second filter, and after the soaking time is ≥5 hours, discharging the waste liquid; and / or When the first flow path is provided with a first discharge valve (F1) and a first emptying valve (F2), after replacing the filter assembly of the first filter (51), the method further comprises: Open the first discharge valve (F1) and the first emptying valve (F2), and fill the first flow path with polyacrylonitrile solution through the metering pump, the feed pipeline after the metering pump and the first discharge valve (F1), until the polyacrylonitrile solution discharged from the first emptying valve (F2) is free of bubbles and gels, and has uniform viscosity and color; and / or When the second flow path is provided with a second discharge valve (F3) and a second emptying valve (F4), after replacing the filter assembly of the second filter (52), the method further comprises: The second discharge valve (F3) and the second emptying valve (F4) are opened, and the polyacrylonitrile solution is charged into the second flow path through the metering pump, the feed pipeline after the metering pump and the second discharge valve (F3), until the polyacrylonitrile solution discharged from the second emptying valve (F4) is free of bubbles and gels, and its viscosity and color are uniform.

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