Polyacrylonitrile polymerization stock solution supply system and filter online switching method thereof

Abstract

The application provides a polyacrylonitrile polymerization stock solution supply system and a filter online switching method thereof, wherein the system comprises a first stock solution tank, a first conveying pump, a metering pump, a first filter and a second filter connected in parallel between a first three-way switching valve and a second three-way switching valve, and the polyacrylonitrile polymerization stock solution supply system further comprises an auxiliary flow path for filter switching, the auxiliary flow path for filter switching comprises a second stock solution tank and a second conveying pump in communication with the second stock solution tank, the outlet end of the second conveying pump is controllably communicated with at least one of a first flow path and a second flow path, and the communication point of the outlet end of the second conveying pump with the first flow path and / or the second flow path is located on the liquid inlet side of the first filter and the second filter. In the application, the pressure of the post-switching flow path is adjusted to the target pressure before the first stock solution tank is switched to the post-switching flow path to supply liquid to the subsequent metering pump, so that the pressure fluctuation at the inlet of the metering pump is more controllable, and the pressure value adjustment is more convenient.

Description

Technical Field

[0001] This invention belongs to the field of polyacrylonitrile polymerization feedstock filtration technology, specifically relating to a polyacrylonitrile polymerization feedstock supply system and its online filter switching method. Background Technology

[0002] Polyacrylonitrile-based carbon fiber is an inorganic fiber material prepared by high-temperature treatment using polyacrylonitrile-based precursor (i.e., polyacrylonitrile fiber) as a precursor. It has been widely used in aerospace, national defense construction, rail transportation, new energy, civil engineering and other fields.

[0003] The stability of polyacrylonitrile (PA) fibers is crucial to the quality of PA-based carbon fiber products. This stability includes changes in fiber structure and properties at individual spinning points over time, differences between different spinnerets at a single spinning point, and variations between different spinning points. Therefore, filtering the polymerization solution (i.e., the PA polymer solution), especially high-viscosity polymerization solutions, is essential before spinning. Filtration removes gel particles and impurities, ensuring the uniformity and spinnability of the polymerization solution and preventing uneven fiber structure and fluctuations in fiber quality. In industrial production, due to relatively poor uniformity within the same batch of polymerization solution, residues from different batches, or prolonged storage time, the pressure difference before and after the filter gradually increases during polymerization solution filtration. When the pressure difference increases to a certain extent, the filtration effect gradually deteriorates over time, requiring timely replacement of the filter element or filter sheet to maintain filtration efficiency.

[0004] The existing methods for filtering polymer raw materials mainly include single-filter filtration and one-on-one-standby-filter filtration. When a single filter needs to replace the filter element, the production line needs to be shut down, resulting in waste of polymer raw materials and affecting the production schedule, which further increases the production cost. Moreover, the workload of disassembling and assembling the filter element is large, and the polymer raw materials are easy to come into contact with air and form new gels. Therefore, in order to save production costs, many companies adopt the one-on-one-standby filtration method. However, there are many problems in the online switching process of the filter, mainly in the following aspects: (1) When the filter is switched online, the pressure fluctuation before the metering pump is large, and the pressure fluctuation range is 0.3MPa~0.5MPa, which cannot meet the requirements for the preparation of high-performance polyacrylonitrile-based carbon fibers; in addition, the high-precision metering pump Large inlet pressure fluctuations make the inlet pressure of the metering pump unstable. If the inlet pressure of the metering pump is too low, the polymer raw material cannot be properly sucked in, affecting the working effect of the pump. If the inlet pressure of the metering pump is too high, it will increase the equipment load and reduce the equipment life. (2) During the online switching process, the valve needs to be opened slowly and the pressure change after the filter should be monitored in time to avoid large pressure fluctuations. This can easily cause misoperation and the operation is cumbersome, making it impossible to achieve online switching with low pressure fluctuations. (3) When switching the filter, dead zones are easily generated, which makes it impossible to discharge the old polymer raw material. This causes the old polymer raw material to enter the spinneret through the metering pump, causing the spinneret to be blocked and affecting normal production.

[0005] In the polyacrylonitrile fiber spinning process, the primary filtration sequence of the polymerization solution is as follows: the polymerization solution first passes through a booster pump, then enters a filter, and finally enters a metering pump for subsequent processes. The polymerization solution used for polyacrylonitrile fiber has unique characteristics such as high viscosity, high molecular weight, and high solid content. Not only must the filtration effect be ensured, but the filtered polymerization solution must also have a certain pressure before entering the metering pump, with a pressure value ≥0.5MPa, to guarantee the inlet pressure of the metering pump, maintain the normal operation of the equipment, and ensure a stable delivery of the polymerization solution. Furthermore, polyacrylonitrile fiber is the foundation for preparing high-performance polyacrylonitrile-based carbon fiber. The uniformity of the linear density, mechanical properties, and microstructure of polyacrylonitrile fiber is crucial. This requires the metering pump to accurately measure, stably transmit, and uniformly supply the solution. The metering pump needs to uniformly supply an equal amount of polymerization solution to the spinneret per unit time. Therefore, high-performance polyacrylonitrile-based carbon fiber requires minimal pressure fluctuation before entering the metering pump, with the pressure fluctuation value controlled within ±0.03MPa. If the pressure fluctuation range is large, it will result in poor uniformity of the linear density, mechanical properties, microstructure and other properties of polyacrylonitrile fibers, and large degree of dispersion within batch, between batches and over long distances. This will not meet the requirements for the preparation of high-performance polyacrylonitrile-based carbon fibers, and may even affect the normal production of fibers. Summary of the Invention

[0006] Therefore, this invention provides a polyacrylonitrile polymerization dosage supply system and its online filter switching method, which can solve the technical problem that in the prior art, when using a standby filter in the polymerization dosage supply system, the pressure fluctuation control operation before the metering pump is difficult during the switching of the standby filter, which is prone to misoperation and thus leads to large pressure fluctuations. This results in poor uniformity of polyacrylonitrile fiber properties such as linear density, mechanical properties, and microstructure, as well as large intra-batch, inter-batch, and long-range dispersion, which cannot meet the requirements for the preparation of high-performance polyacrylonitrile-based carbon fibers and may even affect the normal production of fibers.

[0007] To address the aforementioned problems, this invention provides a polyacrylonitrile polymerization dosage supply system, comprising: a first dosage tank for holding polyacrylonitrile polymerization dosage; a first delivery pump, its inlet end connected to the first dosage tank and its outlet end connected to a first three-way switching valve; a metering pump, its outlet end connected to a spinneret and its inlet end connected to a second three-way switching valve; a first filter and a second filter, connected in parallel between the first three-way switching valve and the second three-way switching valve, to form a first flow path from the first delivery pump through the first filter into the metering pump, and a second flow path from the first delivery pump through the second filter into the metering pump. The polyacrylonitrile polymerization dosage supply system further includes an auxiliary flow path for filter switching, the auxiliary flow path for filter switching comprising:

[0008] The second raw material tank and the second transfer pump connected thereto, wherein the outlet end of the second transfer pump is controllably connected to at least one of the first flow path and the second flow path, and the connection point between the outlet end of the second transfer pump and the first flow path and / or the second flow path is located on the liquid inlet side of the first filter and the second filter.

[0009] In some implementations...

[0010] A first vent valve is provided in the first flow path near the second three-way switching valve, and / or a second vent valve is provided in the second flow path near the second three-way switching valve.

[0011] In some implementations...

[0012] The outlet end of the second delivery pump is connected to the first flow path near the first three-way switching valve via a first on / off valve; and / or, the outlet end of the second delivery pump is connected to the second flow path near the second three-way switching valve via a second on / off valve.

[0013] In some embodiments, the polyacrylonitrile polymerization solution supply system further includes a filter flushing path, the filter flushing path comprising:

[0014] The rinsing solvent tank and a third delivery pump connected thereto are provided. The outlet end of the third delivery pump is controllably connected to either the first flow path or the second flow path. A third vent valve and a fourth vent valve are respectively provided on the first flow path and the second flow path. The connection point between the third delivery pump and the first flow path is the first connection point. The first connection point and the third vent valve are respectively located on the inlet and outlet sides of the first filter. The connection point between the third delivery pump and the second flow path is the second connection point. The second connection point and the fourth vent valve are respectively located on the inlet and outlet sides of the second filter.

[0015] In some implementations...

[0016] The first connection point is located on the raw liquid outlet side of the first filter, and the second connection point is located on the raw liquid outlet side of the second filter; and / or,

[0017] The solvent tank for rinsing is equipped with a heater capable of heating the solvent inside.

[0018] In some implementations...

[0019] A third on / off valve is provided between the first connection point and the third delivery pump, and a fourth on / off valve is provided between the second connection point and the third delivery pump.

[0020] In some implementations...

[0021] The first filter is equipped with a first pressure gauge to detect the real-time pressure of the raw liquid in the first filter; the second filter is equipped with a second pressure gauge to detect the real-time pressure of the raw liquid in the second filter; and / or, both the first three-way switching valve and the second three-way switching valve are T-type three-way valves.

[0022] This invention also provides an online filter switching method, using the aforementioned polyacrylonitrile polymerization stock supply system, comprising:

[0023] Obtain the pressure difference between the inlet and outlet of the second filter in use. When the pressure difference between the inlet and outlet of the second filter exceeds a first preset value, control the auxiliary flow path of the filter to connect with the first flow path, and control the second delivery pump to operate to deliver the polymerized raw material in the second raw material tank to the first filter.

[0024] The system acquires a first real-time pressure value P1 in the first filter and a second real-time pressure value P2 in the second filter. When P1-P2≤P, it controls the auxiliary flow path for filter switching to be cut off from the first flow path. It also controls the first three-way switching valve and the second three-way switching valve to switch so that the polyacrylonitrile polymerization raw material supply system supplies liquid to the metering pump simultaneously from the first flow path and the second flow path. After the real-time pressures in the first filter and the second filter are equal, it controls the first three-way switching valve and the second three-way switching valve to switch so that the polyacrylonitrile polymerization raw material supply system supplies liquid to the metering pump from the first flow path. Here, P is a set pressure difference and P1>P2.

[0025] In some embodiments, when a first vent valve is included, after the auxiliary flow path for filter switching is connected to the first flow path, the first vent valve is controlled to open and closed after fresh polymer stock is discharged from the first vent valve and no bubbles remain; and / or,

[0026] Let P ≤ 0.02 MPa.

[0027] In some embodiments, when a filter flushing flow path is included, after the polyacrylonitrile polymerization solution supply system switches from the second flow path to the first flow path, the filter flushing flow path is controlled to connect with the second flow path, and the third delivery pump is controlled to operate, while the fourth vent valve is controlled to open to flush the second filter online.

[0028] The present invention provides a polyacrylonitrile polymerization solution supply system and its online filter switching method, which has the following beneficial effects:

[0029] An auxiliary flow path for filter switching is added to the existing polymer feedstock supply system, which can be controllably connected to at least one of the first or second flow paths. When one of the first or second filters needs replacement or cleaning, the supply flow path is switched to the other. Before switching the feedstock flow path, the feedstock is supplied to the corresponding flow path via a second feedstock tank and a second delivery pump (e.g., when switching from the second to the first flow path, the feedstock is first supplied to the first flow path). During this process, pressure fluctuations within the flow path supplied by the second feedstock tank (i.e., the switched flow path) will not affect the flow path supplied by the first feedstock tank (i.e., the switched flow path). The pressure fluctuations within the pre-switch flow path are mitigated. After the pressure in the post-switch flow path is adjusted to the target pressure, the first raw material tank is switched to the post-switch flow path to supply liquid to the subsequent metering pump. This makes the pressure fluctuations at the metering pump inlet more controllable and the pressure adjustment more convenient. It effectively avoids the large pressure fluctuations caused by the difficulty in controlling pressure fluctuations when switching filters in the existing technology, which leads to insufficient subsequent production. This improves the uniformity of the linear density, mechanical properties, and microstructure of polyacrylonitrile fibers. The intra-batch dispersion, inter-batch dispersion, and long-range dispersion are all effectively reduced, meeting the requirements for the preparation of high-performance polyacrylonitrile-based carbon fibers and ensuring the normal production of fibers. Attached Figure Description

[0030] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0031] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0032] Figure 1 This is a schematic diagram of the system principle of the polyacrylonitrile polymerization raw material supply system according to an embodiment of the present invention.

[0033] The reference numerals in the attached figures are as follows:

[0034] 1. First raw material tank; 11. Rinse solvent tank; 121. Third on / off valve; 122. Fourth on / off valve; 131. Third vent valve; 132. Fourth vent valve; 14. Heater; 2. Second raw material tank; 31. Second transfer pump; 32. First transfer pump; 33. Third transfer pump; 41. First three-way switching valve; 42. Second three-way switching valve; 51. First on / off valve; 52. Second on / off valve; 61. First pressure gauge; 62. Second pressure gauge; 71. First filter; 72. Second filter; 81. First vent valve;

[0035] 82. Second vent valve; 9. Metering pump; 10. Spinneret; 100. Bellows. Detailed Implementation

[0036] 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 following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0038] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0039] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0040] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0041] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0042] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0043] See Figure 1As shown in the embodiment of the present invention, a polyacrylonitrile polymerization dosing supply system is provided, comprising: a first dosing tank 1 for holding polyacrylonitrile polymerization dosing; a first delivery pump 32, the inlet end of which is connected to the first dosing tank 1 and the outlet end of which is connected to a first three-way switching valve 41; a metering pump 9, the outlet end of which is connected to a spinneret 10 and the inlet end of which is connected to a second three-way switching valve 42; a first filter 71 and a second filter 72, connected in parallel between the first three-way switching valve 41 and the second three-way switching valve 42, to form a first flow path in which the polymerization dosing enters the metering pump 9 from the first delivery pump 32 via the first filter 71, and a second flow path in which the polymerization dosing enters the metering pump 9 from the first delivery pump 32 via the second filter 72. It is understood that, in normal application, the aforementioned first and second flow paths... Only one flow path is used, while the other is used as a backup flow path. That is, assuming that the first flow path is in use, the first filter 71 in it performs the filtration function, while the second filter 72 in the second flow path does not contain the polymerization raw material. It is only used to filter the polymerization raw material sent from the first raw material tank 1 after the pressure difference between the inlet and outlet of the first filter 71 in the first flow path is too large and the filtration performance decreases. The polyacrylonitrile polymerization raw material supply system also includes an auxiliary flow path for filter switching. The auxiliary flow path for filter switching includes: a second raw material tank 2 and a second transfer pump 31 connected to it. The outlet end of the second transfer pump 31 is controllably connected to at least one of the first flow path and the second flow path, and the connection point between the outlet end of the second transfer pump 31 and the first flow path and / or the second flow path is located on the liquid inlet side of the first filter 71 and the second filter 72.

[0044] In this technical solution, an auxiliary flow path for filter switching is added to the existing polymer feedstock supply system. This auxiliary flow path can be controllably connected to at least one of the first or second flow paths. When one of the first filter 71 or the second filter 72 needs to be replaced or cleaned, the feedstock flow path is switched to the other. Before the feedstock flow path is switched, the feedstock is supplied to the corresponding flow path (e.g., when switching from the second flow path to the first flow path, the feedstock is supplied to the first flow path) through the second feedstock tank 2 and the second delivery pump 31. During this process, the pressure fluctuations in the flow path supplied by the second feedstock tank 2 (i.e., the flow path after switching) will not affect the flow path supplied by the first feedstock tank 1 (i.e., the flow path before switching). Pressure fluctuations within the flow path are mitigated. After switching, the pressure in the flow path is adjusted to the target pressure (e.g., 0.01 MPa higher than the original flow path) before switching the first raw material tank 1 to the flow path to supply liquid to the subsequent metering pump 9. This makes the pressure fluctuations at the inlet of the metering pump 9 more controllable and the pressure adjustment more convenient. It effectively avoids the large pressure fluctuations caused by the difficulty in controlling pressure fluctuations when switching filters in the prior art, which leads to insufficient subsequent production. This improves the uniformity of polyacrylonitrile fiber properties such as linear density, mechanical properties, and microstructure. The degree of dispersion within batches, between batches, and long-range dispersion are all effectively reduced, meeting the requirements for the preparation of high-performance polyacrylonitrile-based carbon fibers and ensuring normal fiber production.

[0045] In some embodiments, a first vent valve 81 is provided near the second three-way switching valve 42 in the first flow path, and / or a second vent valve 82 is provided near the second three-way switching valve 42 in the second flow path. The aforementioned first vent valve 81 and second vent valve 82 can be commercially available electromagnetic on / off valves or manually operated ball valves.

[0046] In this technical solution, when the aforementioned filter switching auxiliary flow path is connected to the corresponding first flow path or second flow path, the first vent valve 81 on the first flow path or the second vent valve 82 on the second flow path can be controlled to be in the conducting state, thereby venting the air in the corresponding flow path and further reducing the pressure fluctuation during flow path switching.

[0047] In one specific embodiment, the outlet end of the second delivery pump 31 is connected to the first flow path near the first three-way switching valve 41 via a first on-off valve 51; and / or, the outlet end of the second delivery pump 31 is connected to the second flow path near the second three-way switching valve 42 via a second on-off valve 52. Both the aforementioned first on-off valve 51 and second on-off valve 52 can be implemented using commercially available electromagnetic on-off valves or manual on-off ball valves, enabling control over whether the second delivery pump 31 pumps the polymer raw material from the second raw material tank 2 into the first flow path or the second flow path. Specifically, when the first filter 71 is clogged, the second on-off valve 52 is opened and the first on-off valve 51 is closed; conversely, when the second filter 72 is clogged, the first on-off valve 51 is opened and the second on-off valve 52 is closed.

[0048] In some embodiments, the polyacrylonitrile polymerization solution supply system further includes a filter flushing path, the filter flushing path comprising:

[0049] The rinsing solvent tank 11 and a third transfer pump 33 connected thereto are provided. The outlet end of the third transfer pump 33 is controllably connected to either the first flow path or the second flow path. A third vent valve 131 and a fourth vent valve 132 are respectively installed on the first and second flow paths. The connection point between the third transfer pump 33 and the first flow path is the first connection point, and the first connection point and the third vent valve 131 are located on the inlet and outlet sides of the first filter 71, respectively. The connection point between the third transfer pump 33 and the second flow path is the second connection point, and the second connection point and the fourth vent valve 132 are located on the inlet and outlet sides of the second filter 72, respectively. The aforementioned rinsing solvent tank 11 contains solvents such as dimethyl sulfoxide solution or sodium hydroxide solution, which can dissolve polyacrylonitrile gel.

[0050] In this technical solution, by adding the aforementioned filter flushing flow path, the filter can be flushed online after becoming clogged without needing to be removed from the liquid supply system, greatly improving work efficiency and reducing labor intensity. The solution after filter flushing is discharged from the system through the aforementioned third drain valve 131 or fourth drain valve 132.

[0051] In a preferred embodiment, the first connection point is located on the raw liquid outlet side of the first filter 71, and the second connection point is located on the raw liquid outlet side of the second filter 72. That is, the third vent valve 131 and the fourth vent valve 132 are located on the raw liquid inlet side of the first filter 71 and the second filter 72, respectively.

[0052] In this technical solution, the filter flushing flow path can be reversed to the filter, that is, the flow direction of the solvent is opposite to the flow direction of the polymerization solution. This can thoroughly remove soluble gel in the filter while also flushing out insoluble solid particulate impurities in the reverse phase, thereby improving the cleanliness of the filter.

[0053] In another preferred embodiment, the solvent tank 11 for rinsing is provided with a heater 14 that can heat the solvent inside. The heater 14 can be, for example, an electric heating wire device that can heat the solvent to 60-90°C to ensure its rinsing effect on the gel.

[0054] Specifically, a third on / off valve 121 is provided between the first connection point and the third delivery pump 33, and a fourth on / off valve 122 is provided between the second connection point and the third delivery pump 33. The connection between the solvent and the corresponding filter is realized by controlling the opening and closing of the aforementioned third on / off valve 121 and fourth on / off valve 122, which is convenient and flexible.

[0055] In some implementations...

[0056] The first filter 71 is equipped with a first pressure gauge 61 for detecting the real-time pressure of the raw liquid in the first filter 71; the second filter 72 is equipped with a second pressure gauge 62 for detecting the real-time pressure of the raw liquid in the second filter 72. The ranges of the first pressure gauge 61 and the second pressure gauge 62 are generally selected to be the same. In specific operation, both should be set to be within the operator's field of vision at the same time so that the operator can observe the readings of the two pressure gauges at the same time and achieve precise control of the pressure difference between them.

[0057] Both the first three-way switching valve 41 and the second three-way switching valve 42 are T-type three-way valves, which are mature commercially available components and have the function of simultaneous connection of three ports. This enables the first flow path and the second flow path to supply liquid to the metering pump 9 simultaneously during the online switching process of the filter, thereby achieving the purpose of equalizing the pressure of the raw liquid in the first flow path and the second flow path.

[0058] See also Figure 1 As shown, corrugated pipes 100 are installed between some pipelines, which can effectively reduce the alignment requirements of the pipelines and improve their seismic resistance.

[0059] According to an embodiment of the present invention, an online filter switching method is also provided, which uses the above-described polyacrylonitrile polymerization stock supply system, comprising:

[0060] The pressure difference between the inlet and outlet of the second filter 72 in use is obtained (generally, it can be obtained by two pressure sensors respectively set at the inlet and outlet of the filter). When the pressure difference between the inlet and outlet of the filter exceeds the first preset value (which can be reasonably set according to specific operating requirements), the auxiliary flow path for switching the filter is connected to the first flow path, and the second delivery pump 31 is controlled to operate to deliver the polymerized raw material in the second raw material tank 2 to the first filter 71.

[0061] The system acquires the first real-time pressure value P1 in the first filter 71 and the second real-time pressure value P2 in the second filter 72. When P1-P2≤Pset, it controls the auxiliary flow path for filter switching to be cut off from the first flow path, and controls the first three-way switching valve 41 and the second three-way switching valve 42 to switch the polyacrylonitrile polymerization raw material supply system to supply liquid to the metering pump 9 simultaneously from the first flow path and the second flow path. After the real-time pressures in the first filter 71 and the second filter 72 are equal, it controls the first three-way switching valve 41 and the second three-way switching valve 42 to switch the polyacrylonitrile polymerization raw material supply system to supply liquid to the metering pump 9 from the first flow path, thereby completing the online switching of the second filter 72 to the first filter 71. Here, Pset is the set pressure difference and P1>P2. For the polyacrylonitrile polymerization raw material, the corresponding Pset is ≤0.02MPa to ensure that the pressure fluctuation before the metering pump 9 meets the requirement of not exceeding ±0.03MPa.

[0062] The aforementioned control of the auxiliary flow path for filter switching to be cut off from the first flow path specifically includes controlling the first on / off valve 51 connected to the first flow path to be in a cut-off closed state, and simultaneously controlling the second delivery pump 31 to stop operating.

[0063] In this technical solution, before switching the raw liquid flow path, the raw liquid is first supplied to the corresponding flow path (for example, when switching from the second flow path to the first flow path, the raw liquid is first supplied to the first flow path) through the second raw liquid tank 2 and the second delivery pump 31. During this process, the pressure fluctuation in the flow path supplied by the raw liquid from the second raw liquid tank 2 (i.e., the flow path after switching) will not affect the pressure fluctuation in the flow path supplied by the raw liquid from the first raw liquid tank 1 (i.e., the flow path before switching). After the pressure of the flow path after switching is adjusted to the target pressure (e.g., 0.01 MPa higher than the flow path before switching), the first raw liquid tank 31 is then switched to the first raw liquid tank 31. 1. Switching to the flow path after switching supplies liquid to the subsequent metering pump 9, thereby making the pressure fluctuation at the inlet of metering pump 9 more controllable and the pressure value adjustment more convenient. This effectively avoids the large pressure fluctuations caused by the difficulty in controlling pressure fluctuations when switching filters in the prior art, which leads to insufficient subsequent production. This improves the uniformity of the linear density, mechanical properties, and microstructure of polyacrylonitrile fibers, and effectively reduces the degree of dispersion within batches, between batches, and over long distances, meeting the requirements for the preparation of high-performance polyacrylonitrile-based carbon fibers and ensuring the normal production of fibers.

[0064] It should be noted that in this technical solution, before switching the liquid supply route from the second flow path to the first flow path, the pressure in the first flow path is made slightly higher than the pressure in the second flow path. Then, the first and second flow paths are used simultaneously to supply liquid to the metering pump 9. Since the pressure in the first flow path is slightly higher than the pressure in the second flow path, the raw liquid in the first flow path will flow to the second flow path side, thereby forming a pressure equalization process of the raw liquid in both flow paths. After the pressure is equalized (that is, when the pressure gauges of the two filters show equal values), the aforementioned first three-way switching valve 41 and second three-way switching valve 42 are controlled to allow the first flow path to be used alone to supply liquid to the metering pump 9, resulting in smaller pressure fluctuations before the metering pump 9.

[0065] In some embodiments, when a first vent valve 81 is included, after the auxiliary flow path for filter switching is connected to the first flow path, the first vent valve 81 is controlled to open and closed after the fresh polymer stock solution (i.e., the polymer stock solution from the second stock solution tank 2) discharged from the first vent valve 81 is free of bubbles, thereby ensuring that the pressure difference fluctuation at the inlet of the metering pump 9 is as small as possible after switching from the second flow path to the first flow path for liquid supply.

[0066] In some embodiments, when a filter flushing flow path is included, after the polyacrylonitrile polymerization solution supply system switches from the second flow path to the first flow path, the filter flushing flow path is controlled to connect with the second flow path, and the third delivery pump 33 is controlled to operate. At the same time, the fourth vent valve 132 is controlled to open to flush the second filter 72 online. It is understood that the outlet of the aforementioned fourth vent valve 132 should be equipped with a corresponding waste liquid container or waste liquid discharge pipe.

[0067] In this technical solution, the filter can be flushed online after it becomes clogged without having to be removed from the liquid supply system, which greatly improves work efficiency and reduces labor intensity.

[0068] The above description is merely 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 principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method for online filter switching, characterized in that, The polymerization of polyacrylonitrile is carried out using a polyacrylonitrile polymerization stock supply system, which includes: a first stock tank (1) for holding polyacrylonitrile polymerization stock; a first transfer pump (32) whose inlet end is connected to the first stock tank (1) and whose outlet end is connected to a first three-way switching valve (41); a metering pump (9) whose outlet end is connected to a spinneret (10) and whose inlet end is connected to a second three-way switching valve (42); a first filter (71) and a second filter (72) connected in parallel between the first three-way switching valve (41) and the second three-way switching valve (42) to form a polymerization stock supplied by the first transfer pump (32) through the first filter (10) and the second filter (10). 71) The first flow path into the metering pump (9) and the second flow path into the metering pump (9) via the first transfer pump (32) and the second filter (72) also include an auxiliary flow path for filter switching. The auxiliary flow path for filter switching includes: a second raw material tank (2) and a second transfer pump (31) connected thereto. The outlet end of the second transfer pump (31) is controllably connected to at least one of the first flow path and the second flow path, and the connection point between the outlet end of the second transfer pump (31) and the first flow path and / or the second flow path is located on the inlet side of the first filter (71) and the second filter (72). The online filter switching method includes: Obtain the pressure difference between the inlet and outlet of the second filter (72) in use. When the pressure difference between the inlet and outlet of the raw liquid exceeds the first preset value, control the auxiliary flow path of the filter to connect with the first flow path, and control the second delivery pump (31) to operate to deliver the polymer raw liquid in the second raw liquid tank (2) to the first filter (71). Obtain the first real-time pressure value P1 in the first filter (71) and the second real-time pressure value P2 in the second filter (72). When P1-P2≤P, control the auxiliary flow path for filter switching to cut off from the first flow path. Control the first three-way switching valve (41) and the second three-way switching valve (42) to switch so that the polyacrylonitrile polymerization raw material supply system supplies liquid to the metering pump (9) from the first flow path and the second flow path at the same time. After the real-time pressure in the first filter (71) and the second filter (72) are equal, control the first three-way switching valve (41) and the second three-way switching valve (42) to switch so that the polyacrylonitrile polymerization raw material supply system supplies liquid to the metering pump (9) from the first flow path. Where P is the set pressure difference and P1>P2.

2. The filter online switching method according to claim 1, characterized in that, A first vent valve (81) is provided near the second three-way switching valve (42) in the first flow path, and / or a second vent valve (82) is provided near the second three-way switching valve (42) in the second flow path.

3. The filter online switching method according to claim 2, characterized in that, The outlet end of the second delivery pump (31) is connected to the first flow path near the first three-way switching valve (41) via the first on / off valve (51); and / or, the outlet end of the second delivery pump (31) is connected to the second flow path near the second three-way switching valve (42) via the second on / off valve (52).

4. The filter online switching method according to any one of claims 2 to 3, characterized in that, It also includes a filter flushing flow path, which includes: The solvent tank (11) for rinsing and the third delivery pump (33) connected thereto are provided with a third vent valve (131) and a fourth vent valve (132) respectively. The outlet end of the third delivery pump (33) is controllably connected to either the first flow path or the second flow path. The first flow path and the second flow path are respectively provided with a third vent valve (131) and a fourth vent valve (132). The connection point between the third delivery pump (33) and the first flow path is the first connection point. The first connection point and the third vent valve (131) are respectively located on the inlet and outlet sides of the first filter (71). The connection point between the third delivery pump (33) and the second flow path is the second connection point. The second connection point and the fourth vent valve (132) are respectively located on the inlet and outlet sides of the second filter (72).

5. The filter online switching method according to claim 4, characterized in that, The first connection point is located on the raw liquid outlet side of the first filter (71), and the second connection point is located on the raw liquid outlet side of the second filter (72); and / or, The solvent tank (11) for rinsing is equipped with a heater (14) that can heat the solvent inside.

6. The filter online switching method according to claim 4, characterized in that, A third on / off valve (121) is provided between the first connection point and the third delivery pump (33), and a fourth on / off valve (122) is provided between the second connection point and the third delivery pump (33).

7. The filter online switching method according to claim 4, characterized in that, After the auxiliary flow path for filter switching is connected to the first flow path, the first vent valve (81) is opened and closed after fresh polymer stock solution is discharged from the first vent valve (81) and no bubbles are present; and / or, Let P ≤ 0.02 MPa.

8. The filter online switching method according to claim 4, characterized in that, After the polyacrylonitrile polymerization raw material supply system switches from the second flow path to the first flow path, the filter flushing flow path is controlled to connect with the second flow path, and the third delivery pump (33) is controlled to operate. At the same time, the fourth vent valve (132) is controlled to open to flush the second filter (72) online.

9. The filter online switching method according to claim 1, characterized in that, The first filter (71) is equipped with a first pressure gauge (61) for detecting the real-time pressure of the raw liquid in the first filter (71); the second filter (72) is equipped with a second pressure gauge (62) for detecting the real-time pressure of the raw liquid in the second filter (72); and / or, the first three-way switching valve (41) and the second three-way switching valve (42) are both T-type three-way valves.

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