CN108556305B

CN108556305B - Filtering system

Info

Publication number: CN108556305B
Application number: CN201810338279.2A
Authority: CN
Inventors: 施建强; 姚强; 石教学; 张祥; 陈琳琳
Original assignee: Shanxi Xiaohuangfeng Intelligent Equipment Co ltd; Zhejiang Lyuyu Environmental Protection Co ltd
Current assignee: Shanxi Xiaohuangfeng Intelligent Equipment Co ltd; Zhejiang Lyuyu Environmental Protection Co ltd
Priority date: 2018-04-16
Filing date: 2018-04-16
Publication date: 2023-09-26
Anticipated expiration: 2038-04-16
Also published as: CN108556305A

Abstract

The invention discloses a filtering system, which at least comprises a first booster pump, a first filter, a second booster pump, a second filter and a control unit which are connected in sequence; the first filter is a double-column backflushing screen-changing filter; the second filter is an automatic melt backflushing filter; the control unit is respectively connected with two pressure sensors positioned at two sides of the first filter, pressure sensors positioned at two sides of the second filter, the first booster pump, the first filter, the second booster pump and the second filter. The invention also discloses an operation process of the filtering system. According to the invention, the automatic flushing of the filter screen of the second filter is realized, when the pressure difference between the melt outlet and the melt inlet of the second filter is overlarge, the back flushing process is automatically started, and the position and the moving distance of the back flushing shaft of the filter of the second filter are accurately controlled; the circuit structural design is reasonable, the pertinence of the high-temperature melt filtration is high, the filtration period is long, frequent replacement of the filter is avoided, the filtration is stable, and the filtration efficiency is high.

Description

Filtering system

Technical Field

The invention belongs to the field of filtering equipment, and particularly relates to a filtering system suitable for high-temperature melt.

Background

At present, the filtering of materials is generally carried out in a single-filter filtering mode, the pertinency is low, the filtering effect is poor, and impurities such as gel formed at high temperature in the chemical reaction process, carbonization caused by long-term heat history and the like need to be removed in the PET thermoplastic polyester production process, so that the filtering process is often involved. The original polyester has short heat history and low impurity content, the technical scheme that a candle filter is arranged before final polycondensation is adopted, the regenerated polyester is produced by taking bottle flakes, waste silk and waste textiles as raw materials, the sources and the components are complex, the impurity content is high, the components such as spinning oil, printing and dyeing auxiliary and the like in the raw materials are easy to degrade, carbonize and generate gel, and if primary filtration is adopted, the service cycle of the filter is extremely short and the filter is replaced frequently, so that the production of the regenerated polyester needs to be designed with multi-stage filtration.

On the other hand, because of high impurity content, the regenerated polyester production process mostly adopts a filter capable of being back-flushed on line, and when the filter is blocked, the filter can be back-flushed, and meanwhile, the normal conveying process is uninterrupted. However, when a conventional backflushing filter backflushes, 25% of the melt flux is used for backflushing, and only 75% of the melt can be normally transported.

Therefore, the two-stage filter is arranged, the filtering precision is sequentially improved, the filtering effect can be improved, the service life of the filter is prolonged, and the influence of backflushing on the normal melt conveying efficiency is reduced.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a filter system which has high pertinence, high filter efficiency, good filter effect and long service life.

The technical scheme adopted for solving the technical problems is as follows: a filtering system at least comprises a first booster pump, a first filter, a second booster pump, a second filter and a control unit which are connected in sequence;

the first filter is a double-column backflushing type screen-changing filter and comprises a plunger, one end of the plunger is inserted into the filter screen cavity, and the other end of the plunger is connected with the hydraulic cylinder; the plunger is communicated with the filter screen cavity, a diamond melt channel is arranged in the filter screen cavity, and a pressure sensor and a melt inlet, a pressure sensor and a melt outlet are arranged in the filter screen cavity; the filter screen cavity is provided with a back flushing channel, and the diamond melt channel and the back flushing channel form two states of being staggered and communicated with each other;

the second filter is an automatic melt backflushing filter and at least comprises a cylindrical barrel and a central control system, wherein a filter backflushing shaft, a filter disc, a filter screen and a supporting framework are arranged in the center of the barrel; the bottom of the cylinder body is provided with a melt inlet, the upper part of the cylinder body is provided with a melt outlet, and pressure sensors are arranged at the melt inlet and the melt outlet; a plurality of symmetrical transverse backflushing channels are arranged on the backflushing shaft of the filter; the supporting framework forms a plurality of S-shaped melt flow passages; the transverse recoil channels and the melt flow channels are mutually staggered and communicated one by one;

the control unit is respectively connected with two pressure sensors positioned at two sides of the first filter, pressure sensors positioned at two sides of the second filter, the first booster pump, the first filter, the second booster pump and the second filter, and when the pressure difference of the two pressure sensors at the liquid inlet and the liquid outlet of the first filter reaches a set value, the control unit regulates the first booster pump to increase the flux when detecting that the first filter is backwashed; when the pressure difference of two pressure sensors at the liquid inlet and the liquid outlet of the second filter reaches a set value, the control unit adjusts the first booster pump and the second booster pump to synchronously increase flux when detecting that the second filter is backwashed; the control unit is also used for controlling the first filter and the second filter to start the back flushing program at the same time.

The central position of the second filter is provided with the filter backflushing shaft, and the connection between a plurality of transverse backflushing channels on the filter backflushing shaft and the melt flow channel is controlled by the up-down movement of the filter backflushing shaft, so that the filter screen is automatically washed, the cleaning efficiency is high, the cleaning effect is good, the filter and the cleaning can be in seamless butt joint, and a plurality of disassembly and assembly procedures are saved; the arrangement of the central control system realizes the accurate control of the up-and-down movement of the filter backflushing shaft, is convenient for the alignment of the transverse backflushing channel and the melt flow channel, and is also convenient for controlling the up-movement distance of the filter backflushing shaft; the pressure sensors of the melt inlet and the melt outlet are arranged, so that the impurity accumulation condition on the filter screen in the filter is conveniently monitored, the back flushing of the filter screen is conveniently and timely carried out, and the orderly filtration is ensured.

The first filter can perform online recoil, the filter screen is disposable, the replacement is convenient, the use cost is low, but the filter effect is poor, the precision is low, the filter screen is not suitable for filtering under high pressure, the filter screen is easy to break down, and the filter screen is suitable for filtering inorganic impurities above 20 microns; the second filter can be back-flushed on line, the filter has long service life and high filtering precision, but the filter screen has insufficient pressure resistance, and is suitable for being used as a primary filter for regenerating high impurity-containing media such as polyester melt; the invention combines the first filter and the second filter, combines the advantages of the first filter and the second filter, effectively avoids the problems of overhigh pressure, serious degradation and increased color value caused by singly using one filter, does not have the situation that color matching is difficult to control in the subsequent dyeing process, prevents the later cleaning difficulty caused by the excessive use state of the single filter, shortens the service life, increases the normal transmission melt channel, prolongs the service life of the filter, has long filtering period, avoids frequent filter replacement, has better adaptability to high-temperature melt filtration and has high filtering precision.

Further, at least two second filters are arranged, when the filter works, the transverse backflushing channels and the melt flow channels are mutually staggered, the transverse backflushing channels are closed, the melt enters the melt flow channels through the melt inlets, passes through the filter screen downwards, and flows out of the second filters upwards; during backflushing, the central control system controls the filter backflushing shaft to move, the transverse backflushing channels are communicated with the melt flow channels one by one, the melt backflushes the filter screen, and the melt enters the filter backflushing shaft through the transverse backflushing channels and is discharged.

Further, the at least two second filters are arranged on different branches and are respectively connected with the second booster pump through multi-way valves. The arrangement of the two second filters ensures normal filtration, when one of the second filters is in a standby state, the other second filter can be started to work when one of the second filters is back washed, and continuous and stable filtration is ensured.

Further, pressure sensors are arranged at the melt inlet and the melt outlet of the second filter, when the pressure difference reaches a set value, the central control system controls the discharge valve at the bottom of the filter backflushing shaft to open and controls the filter backflushing shaft to move according to the pressure difference signal, the central control system controls the transverse backflushing channel to be communicated with the melt flow channel by setting the moving position of the filter backflushing shaft, and the central control system controls the moving distance of the filter backflushing shaft by setting the residence time.

Further, a jacket is arranged outside the cylindrical barrel, and the temperature of the jacket is 250-270 ℃. The temperature of the melt in the filter is ensured by the arrangement of the jacket, and the melt is prevented from excessively dropping in the filtering process, so that the influence on the subsequent process is avoided.

Further, a discharge pipe is arranged at the melt inlet of the second filter. The initial stage that the fuse-element flowed into the second filter, the velocity of flow and the flow of fuse-element are not very stable, open row material pipe this moment, discharge the fuse-element of anterior segment, after the supply of fuse-element reaches steady state, close row material pipe again, guide into the second filter with the fuse-element and filter, guarantee filterable stability.

Further, an exhaust port is arranged at the melt outlet of the second filter. When the melt flows into the second filter, the exhaust port is opened, air in the second filter is extruded and discharged, and after the melt is completely or nearly completely filled in the filter, the exhaust port is closed for normal filtration, so that the phenomenon that the relative pressure is excessive due to the fact that excessive air is accumulated in the second filter and the circulation of the melt in the second filter is influenced is avoided.

Further, a stroke sensor matched with the central control system and used for controlling the moving distance of the filter recoil shaft is arranged at the end part of the filter recoil shaft.

Further, the filtering precision of the first filtering device is 20-60 micrometers; the second filter device has a filtration accuracy of 20-40 microns. The gradient arrangement of different filter accuracies prolongs the service cycle of the filter and avoids frequent replacement of the filter.

Further, the ratio of the number of the transverse recoil channels to the number of the melt channels is less than or equal to 10%. Assuming that the melt flow channels are 100 groups, when only 1 transverse backflushing channel is arranged on the backflushing shaft of the filter, the backflushing shaft of the filter needs to move 100 times to complete the whole backflushing process, and the normal melt flux of the filter is 99%; if the number of the transverse backflushing channels is 4, the backflushing process is completed only by 25 times, the normal flux of the melt during backflushing is 96%, that is, the more the number of the transverse backflushing channels is, the faster the backflushing is, but the less the normal flux of the melt is, the frequent fluctuation of the melt at the outlet of the filter during the backflushing is, and the fluctuation of the melt pressure is set within 10%, so that the result of considering the flux of the melt and the backflushing efficiency is achieved, and the fluctuation of the pressure during the backflushing can be reduced.

The invention also discloses an operation process of the filtering system, which comprises the following steps:

1) Setting the pressure difference of the two side pressure sensors of the first filter to be 10-40bar, setting the pressure difference of the two side pressure sensors of the second filter to be 30-100bar, and setting the backflushing frequency value of the second filter on any branch;

2) Adjusting the first booster pump such that the inlet pressure of the first filter melt is greater than 65bar;

3) Closing a discharge valve of the second filter, opening a discharge pipe for discharging for 10-80 minutes, opening an exhaust port, and continuously filtering when the melt enters the large channel from the inlet valve at a flow rate of 0.2-2t/h and enters the melt flow channel through a liquid inlet hole on the side wall of the large channel for step-by-step filtration, and closing the exhaust port when the melt is full of the whole cylinder;

4) When the pressure difference value of the pressure sensors at the two sides of the first filter is higher than a set value, the first filter starts back flushing, the control unit adjusts the first booster pump to increase flux, and the second booster pump adjusts to maintain the pressure at the liquid outlet of the first filter unchanged, so that the first filter is in a normal filtering state;

5) When the pressure difference value of the pressure sensors at the two sides of the second filter is ultrahigh, the second filter starts back flushing, the central control system controls the discharge valve to be opened, the back flushing shaft of the filter automatically moves downwards, the transverse back flushing channels are communicated with the melt flow channels one by one, the melt backflushes the filter screen, enters the back flushing shaft of the filter through the transverse back flushing channels and is discharged, and the control unit adjusts the first booster pump and the second booster pump to synchronously increase flux;

6) When the first filter filters normally and the recoil frequency of the second filter is monitored to be higher than a set value, the control system adjusts the multi-way valve to guide the melt of the branch to the other branch, and the melt is filtered through the standby second filter.

The beneficial effects of the invention are as follows: the automatic flushing of the filter screen of the second filter is realized, when the pressure difference between the melt outlet and the melt inlet of the second filter is overlarge, a back flushing process is automatically started, and the position and the moving distance of a back flushing shaft of the filter of the second filter are accurately controlled; the circuit structural design is reasonable, and the pertinence to the filtration of high temperature fuse-element is high, and filtration cycle is long, avoids frequent change filter, and the filtration is stable, and filtration efficiency is high, and the filter effect is good.

Drawings

Fig. 1 is a schematic flow structure of the present invention.

Fig. 2 is a schematic diagram of a plunger structure of a first filter according to the present invention.

Fig. 3 is a front view of the first filter of the present invention in normal use.

Fig. 4 is a side view of the first filter of the present invention in normal use.

Fig. 5 is a top view of the first filter of the present invention in normal use.

Fig. 6 is a top view of a first filter of the present invention in a backwashed condition.

Fig. 7 is a top view of an alternative backwash of a first filter according to the present invention.

Fig. 8 is a schematic diagram showing a normal filtering state of the second filter according to the present invention.

FIG. 9 is a schematic view of the structure of a filter backflushing shaft of the second filter of the present invention.

Fig. 10 is a schematic view showing a part of the structure of the filter screen and the supporting frame of the second filter according to the present invention.

FIG. 11 is a schematic representation of the backwash state of the second filter of the present invention.

Detailed Description

In order to make the present invention better understood by those skilled in the art, the following description of the technical solutions of the present invention will be made in detail, but not all embodiments of the present invention are apparent to some embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

As shown in figure 1, the filtering system is suitable for high impurity content regenerated melt, and comprises a first booster pump 11, a pressure sensor 1, a first filter, a pressure sensor 2, a second booster pump 12, a pressure sensor 3, at least two paths of filtering branches which are connected through a multi-way valve and are all provided with second filters, a pressure sensor 4 connected to the rear end of the second filter and a control unit respectively connected with the structures, wherein the control unit can control the back flushing actions of the first filter and the second filter to be asynchronous, and the control unit is especially connected with a central control system of the second filter.

When the pressure difference between the pressure sensor 1 and the pressure sensor 2 at the two sides of the first filter reaches a set value, the first filter automatically starts back flushing, and at the moment, the control unit senses that the first filter performs back flushing, the first booster pump flux automatically increases to balance the flow reduction caused by back flushing because of the reduction of normal melt flow during back flushing, and the second booster pump automatically adjusts to maintain the pressure of the pressure sensor 2 unchanged, ensure that enough pressure is used for back flushing, and maintain the pressure stability of the subsequent working procedure.

When the pressure difference between the pressure sensor 3 and the pressure sensor 4 at two sides of the second filter reaches a set value, the second filter automatically starts back flushing, and when the control unit senses that the second filter performs back flushing, the flux of the first booster pump and the flux of the second booster pump are synchronously increased so as to offset the flux reduction during back flushing, and meanwhile, the pressure of the pressure sensor 4 is kept unchanged.

When the control unit senses that the backflushing frequency of the second filter is higher than a set value, the second filter is considered to be invalid, and the multi-way valve is automatically controlled to guide the melt to the second filter on the other standby branch. If the second filter is in a normal state, the second filter is backflushed for 10 times a day, namely, for 2.4 hours, and the backflushing frequency is changed to be 2 hours or 1.5 hours once, namely, the second filter is judged to be invalid, and specific numerical values can be set according to specific conditions.

As shown in fig. 2-7, the first filter is a double-column backflushing type screen-changing filter 2, the filtering precision is 20-60 micrometers, the filter comprises a plunger 21, a distributing plate 22, a closing slide valve, a screen-changing device cavity 26 and a hydraulic cylinder 28, two cavities which are respectively called a first cavity 211 and a second cavity 212 are symmetrically arranged on the side wall of the plunger 21, the distributing plate 22, a filter screen group 23 and a filter screen guard ring 24 are respectively arranged in the first cavity 211 and the second cavity 212, the distributing plate 22 is of a hemispherical structure, the spherical surface of the distributing plate faces the interior of the plunger 21, the filter screen group 23 is arranged on the other surface of the distributing plate, the filter screen group 23 is composed of two layers of skeleton nets 231 and two layers of fine nets 232, the two layers of fine nets 232 are sequentially arranged, the precision is 100 micrometers, the two layers of skeleton nets 231 are positioned on the left side and the right side of the fine nets 232, and the outer side of the filter screen group 23 is fixed by the filter screen guard ring 24; one end of the plunger 21 provided with a cavity is arranged in the screen changer cavity 26, and the other end is connected with a position rod 281 of the hydraulic cylinder 28; a diamond-shaped melt runner is arranged in the screen changer cavity 26 and is communicated with the cavity of the plunger 21, the melt runner penetrates through the screen changer cavity 26, one end of the melt runner is provided with a melt inlet 261, the other end of the melt runner is provided with a melt outlet 264, the melt runner is composed of a melt runner I262 and a melt runner II 263 which are symmetrically arranged, the melt runner I262 and the melt runner II 263 are symmetrically arranged by the center line of the melt inlet 261, and the tail ends of the melt runner I and the melt runner II are converged at the melt outlet 264; a closing slide valve is arranged on the screen changer cavity 26 at one side of the melt inlet 261, a back flushing port 25 is arranged on the closing slide valve, and the back flushing port 25 is communicated with the cavity of the plunger 21 through a back flushing flow passage 251; a pressure sensor is provided on the distributor plate 22, which pressure sensor is connected to the hydraulic cylinder 28 and the shut-off slide valve for the transmission of pressure signals. The plungers 21 are provided with two plungers 21a and 21b, respectively, the plunger 21b is located under the plunger 21a and symmetrically arranged by taking the central line of the screen changer cavity 26 as a symmetrical axis, each plunger 21 corresponds to one hydraulic cylinder 28, wherein the hydraulic cylinder corresponding to the plunger 21a is called a hydraulic cylinder 28a, the hydraulic cylinder corresponding to the plunger 21b is called a hydraulic cylinder 28b, each corresponding hydraulic cylinder 28 is provided with a position rod 281, and each position rod 281 corresponds to one plunger 21.

Under normal conditions, the melt enters a first melt flow channel 262 and a second melt flow channel 263 respectively from an inlet 261, is distributed by a distribution plate 22 and is filtered by a filter screen group 23, the melt is firstly subjected to rough filtration by a framework screen 231, is subjected to fine filtration by two layers of fine filter screens 232, passes through one framework screen 231, and flows out from a melt outlet 264 at the other end of the screen changer cavity 26, so that normal melt filtration and supply work is completed; as the filtration proceeds, the impurity on the filter screen group 23 gradually accumulates, the melt pressure rises along with the rising, when the pressure sensor detects that the melt pressure on the first plunger 21a reaches a set value, in this embodiment, the pressure sensor sets the pressure difference to be 10-40bar, the pressure sensor sends out the signal, the first hydraulic valve 28a pushes the first plunger 21a to move outwards through the position rod, the filter screen group 23 and other parts corresponding to the left side of the first plunger 21a are disconnected with the first melt flow channel 262 and are communicated with the back flushing flow channel 251 corresponding to the back flushing port, a small part of the melt in one end of the melt flow channel of the melt outlet 264 flows backwards, the impurity accumulated on the filter screen group 23 is carried out, when the pressure on the filter screen group 23 is lower than the set value, the first plunger 21a moves backwards under the action of the first hydraulic cylinder 28a and resets, the back flushing flow channel 251 is disconnected with the first plunger 21a, the first plunger 21a is communicated with the first melt flow channel 262, and normal melt filtration and transportation are continued; similarly, when the pressure of the filter screen group 23 on the right side of the plunger one 21a exceeds a set value, the plunger one 21a moves backward, and the right filter screen group is communicated with the backwash flow passage on the right side, so that backwash of the right filter screen group is performed.

When the back flushing can not remove impurities, the hydraulic cylinder 28 can push the plunger 21 to move outwards until the filter screen group 23 leaks out of the screen changer cavity 26, at the moment, the filter screen guard ring 24 is removed, the filter screen group 23 can be taken down, the filter screen group 23 can be recycled after deep cleaning, and the screen changing interval time is greatly prolonged; because the two plungers 21 are symmetrically arranged on two sides of the symmetry axis of the screen changer cavity 26, a screen changer mode can be adopted, and the material flow pressure is not changed, the flow speed is stable, instant current interruption and melt leakage are avoided in the screen changing and back flushing processes, so that the continuous production can be realized for a long time; in the process of automatically cleaning the filter screen at one time, the aim of cleaning the filter screen can be fulfilled, the backwash efficiency is high, production pause is avoided, the yield is increased, the energy is saved, and the production cost is saved; greatly reduces the screen changing frequency and avoids frequent screen changing.

As shown in fig. 8-11, the second filter has a filtering precision of 20-40 micrometers, and at least comprises a cylindrical hollow cylinder 5 and a central control system, wherein a filter backflushing shaft 6, a filter disc 71, a filter screen 72 and a supporting framework 73 are arranged in the cylinder 5, the center of the filter backflushing shaft 6 is a hollow discharging channel 62, and a discharging valve is arranged at the bottom of the discharging channel 62. Specifically, a hollow cylindrical large channel 53 is arranged at the central axis of the cylinder 5, a plurality of groups of liquid inlets are formed in the side wall of the large channel 53 along the height direction of the large channel, and each group of liquid inlets comprises a plurality of liquid inlets symmetrically arranged on the same horizontal plane; a filter backflushing shaft 6 is arranged in the large channel 53 in a vertically movable manner, a plurality of groups of backflushing channels are arranged on the filter backflushing shaft 6 along the height direction of the filter backflushing shaft, each group of backflushing channels comprises a plurality of transversely arranged and symmetrical transverse backflushing channels 61, and the transverse backflushing channels 61 are communicated with a discharge channel 62 in the filter backflushing shaft 6; the top of the filter recoil shaft 6 is provided with a filter disc 71, and the filter disc 71 is an annular sintered felt or mat-type net, and the outer diameter of the filter disc is matched with the inner diameter of the large channel 53 and is in sealing fit with the large channel 53.

The supporting framework 73 comprises an upper supporting net 731 and a lower supporting net 732 which are arranged in parallel up and down with the large channel 53 as a center, a fixing piece 733 used for connecting the ends of the upper supporting net 731 and the lower supporting net 732, the plurality of upper supporting nets 731 and the lower supporting net 732 are arranged to form a supporting framework 73 with the cross section of S, the filter screen 72 is arranged between the upper supporting net 731 and the lower supporting net 732, thus the filter disc 71, the filter screen 72 and the supporting framework 73 form a plurality of S-shaped melt flow channels 74, and the melt flow channels 74 are arranged in opposite communication with the liquid inlet holes. A gap 54 for the filtered liquid to flow is reserved between the outer side of the supporting framework 73 and the inner wall of the cylinder body 5.

The bottom of the cylinder 5 is provided with a melt inlet 51 with an inlet valve, the melt inlet 51 is provided with a pressure sensor 3 which senses that the feeding pressure of the melt is more than 65bar, and a discharge pipe 511 is also arranged at the melt inlet 51; the upper part of the cylinder 1 is provided with a melt outlet 52 with an outlet valve, the melt outlet 52 is also provided with a pressure sensor 4 which senses that the feeding pressure of the melt is more than 4bar, and the melt outlet 52 is also provided with an exhaust port 521.

When filtering, the transverse backflushing channels 61 and the liquid inlet holes are staggered, namely, the transverse backflushing channels 61 are propped against the inner wall of the large channel 53, so that the transverse backflushing channels 61 are in a closed state, at the moment, the melt enters the melt flow channel 74 through the melt inlet 51, flows upwards through the gap 54 between the supporting framework 73 and the inner wall of the cylinder 5 after being filtered by the filter screen 72 downwards along the arrow direction, and finally flows out of the filter from the melt outlet 52.

In order to ensure the stability of filtration, before the melt enters the filter through the melt inlet 51, the inlet valve of the melt inlet 51 is closed, a part of the melt with unstable feeding is discharged through the discharge pipe 511, and after the feeding is stable, the inlet valve is opened to allow the melt to normally enter the filter, specifically, in the embodiment, the feeding flow rate of the melt is ensured to be 0.2-2t/h; at this time, the outlet valve of the melt outlet 52 is kept in a closed state, the vent is opened, and as the melt enters, the gas in the filter is gradually exhausted through the vent until the barrel 5 is full of the melt, the vent 521 is closed, and the outlet valve is opened for normal filtration. The above actions form a protection program, which has good protection effect on the filter.

The bottom end of the filter recoil shaft 6 is provided with a travel sensor which is connected with a central control system and used for controlling the moving distance of the filter recoil shaft 6; the bottom of the cylinder 5 is provided with a locator connected with a central control system.

When the pressure difference between the two pressure sensors at the melt inlet 51 and the melt outlet 52 reaches 40bar after filtration is carried out for a period of time, a signal is sent to a central control system, the central control system receives the pressure difference signal and then controls a discharge valve to be opened, meanwhile, the filter backflushing shaft 6 moves downwards, when a transverse backflushing channel moving to the bottommost end of the filter backflushing shaft 6 is communicated with a melt flow channel at the bottommost part of the barrel 5, a positioner sends a signal to a control unit to control the filter backflushing shaft 6 to stop moving downwards, the default position is 0 point, a backflushing action is started, at the moment, the filtered melt flows downwards from the top of the barrel, the accumulated attachments on the filter screen 72 are washed downwards through a filter screen 72, the washed liquid passes through a liquid inlet of a large channel 53 from the melt flow channel 74 and is discharged from the bottom of a discharge channel 62 of the filter backflushing shaft 6 through a transverse backflushing channel 61. After the filter backflushing shaft 6 stays at the 0-point position for 10-60s, the central control system controls the filter backflushing shaft 6 to start moving upwards, the moving distance is controlled by the stroke sensor, backflushing is performed sequentially from bottom to top until backflushing of all filter screens is completed, and the discharge valve is closed. Specifically, when the support framework has 100 groups, the filter backflushing shaft is provided with 4 groups of transverse backflushing channels, and the filter backflushing shaft needs to be moved 25 times at the moment, so that a complete backflushing process is completed. In this embodiment, the ratio of the number of the transverse backflushing channels to the number of the melt channels is less than or equal to 10%, preferably 10%, so as to reduce the pressure fluctuation during backflushing, as shown in table 1, even if the normal melt channels reach more than 90% during backflushing, the pressure fluctuation is less than 10%, and the pressure fluctuation of 10% is regulated by the first booster pump and the second booster pump, so that the continuous and stable filtration is ensured.

TABLE 1 influence of the ratio of the number of Filter screens to the number of Filter backflushing shafts on the filtration

A jacket (not shown in the figure) is arranged outside the cylinder 5, and is arranged to cover the outer wall of the whole cylinder 5, and the temperature of the jacket is 260-330 ℃, so that the melt in the cylinder 5 can be ensured to have higher temperature in the filtering process.

The operation process of the filtering system comprises the following steps:

1) Setting the pressure difference value between the two side pressure sensors 1 and 2 of the first filter to be 10-40bar, setting the pressure difference between the two side pressure sensors 3 and 4 of the second filter to be 30-100bar, and setting the backflushing frequency value of the second filter on any branch to be 2-20 times per day;

4) Maintaining the outlet pressure of the second filter greater than 40bar;

5) When the pressure difference value of the pressure sensors at the two sides of the first filter is higher than a set value, the first filter starts back flushing, the control unit adjusts the first booster pump to increase flux, the second booster pump adjusts to maintain the pressure at the liquid outlet of the first filter unchanged, the pressure is maintained at 20-200bar, and the first filter is in a normal filtering state;

6) When the pressure difference value of the pressure sensors at the two sides of the second filter is ultrahigh, the second filter starts back flushing, the central control system controls the discharge valve to be opened, the back flushing shaft of the filter automatically moves downwards, a transverse back flushing channel at the lowest end of the back flushing shaft of the filter is communicated with a melt flow channel at the lowest part of the cylinder body, the melt backflushes the filter screen, and the melt enters the back flushing shaft of the filter through the transverse back flushing channel and is discharged, so that back flushing of part of the filter screen is completed; the filter backflushing shaft moves upwards until the backflushing of all filter screens is completed; simultaneously, the control unit adjusts the first booster pump and the second booster pump to synchronously increase flux;

7) When the back flushing frequency of the second filter is monitored to be higher than a set value, the control system adjusts the multi-way valve to guide the melt of the branch to the other branch, and the melt is filtered through the standby second filter;

8) Repeating the above process to complete the filtering process.

Description of experimental data

Before the melt enters the filter: the pipe diameter is 25-100mm, the pipe temperature is 290-298 ℃, the intrinsic viscosity is 0.68dl/g, the kinematic viscosity is 250-300Pa [ S ], the flow rate is 1.5-3m/min, the b value is 3, and the impurity content (calculated by ash content, 0.45%) is realized.

The melt filtrate is obtained by respectively utilizing the independent filtration of the first filter, the independent filtration of the second filter and the combined filtration of the invention.

*1 impurity content of the final product: the ash content is used for representing the impurity content of the final product, and the good and bad filtering effect is reflected. *2b value: the yellow-blue index of the polyester product reflects the degradation of the polyester due to the temperature rise.

The foregoing detailed description is provided to illustrate the present invention and not to limit the invention, and any modifications and changes made to the present invention within the spirit of the present invention and the scope of the appended claims fall within the scope of the present invention.

Claims

1. A filtering system at least comprises a first booster pump, a first filter, a second booster pump, a second filter and a control unit which are connected in sequence;

the first filter is a double-column backflushing type screen-changing filter (2) and comprises a plunger (21), one end of the plunger (21) is inserted into a filter screen cavity, and the other end of the plunger is connected with a hydraulic cylinder (28); the plunger (21) is communicated with a filter screen cavity, a diamond melt channel is arranged in the filter screen cavity, and a pressure sensor and a melt inlet (261) and a pressure sensor and a melt outlet (264) are arranged in the filter screen cavity; the filter screen cavity is provided with a back flushing channel (251), and the diamond melt channel and the back flushing channel (251) form two states which are mutually staggered and communicated;

the second filter is an automatic melt backflushing filter and at least comprises a cylindrical barrel (5) and a central control system, wherein a filter backflushing shaft (6), a filter disc (71), a filter screen (72) and a supporting framework (73) are arranged in the center of the barrel (5); the bottom of the cylinder body (5) is provided with a melt inlet (51), the upper part of the cylinder body is provided with a melt outlet (52), and pressure sensors are arranged at the melt inlet (51) and the melt outlet (52); a plurality of symmetrical transverse backflushing channels (61) are arranged on the backflushing shaft (6) of the filter; the supporting framework (73) forms a plurality of S-shaped melt flow passages (74); the transverse recoil channels (61) and the melt flow channels (74) are in a mutually staggered and one-by-one communicated state;

the control unit is respectively connected with two pressure sensors positioned at two sides of the first filter, pressure sensors positioned at two sides of the second filter, the first booster pump, the first filter, the second booster pump and the second filter, and when the pressure difference of the two pressure sensors at the liquid inlet and the liquid outlet of the first filter reaches a set value, the control unit regulates the first booster pump to increase the flux when detecting that the first filter is backwashed; when the pressure difference of two pressure sensors at the liquid inlet and the liquid outlet of the second filter reaches a set value, the control unit adjusts the first booster pump and the second booster pump to synchronously increase flux when detecting that the second filter is backwashed; the control unit is also used for controlling the first filter and the second filter to start the back flushing program at the same time;

at least two second filters are arranged, when the two second filters work, the transverse backflushing channels (61) and the melt flow channels (74) are staggered, the transverse backflushing channels (61) are closed, the melt enters the melt flow channels (74) through the melt inlet, passes through the filter screen (72) downwards, and flows out of the second filters upwards; during backflushing, the central control system controls the filter backflushing shaft (6) to move, the transverse backflushing channels (61) are communicated with the melt flow channels (74) one by one, and the melt backflushing filter screen (72) enters the filter backflushing shaft (6) through the transverse backflushing channels (61) and is discharged;

and when the pressure difference reaches a set value, a central control system controls a discharge valve at the bottom of the filter backflushing shaft (6) to open and controls the filter backflushing shaft (6) to move according to a pressure difference signal, the central control system controls the transverse backflushing channel (61) to be communicated with the melt flow channel (74) by setting the moving position of the filter backflushing shaft (6), and the central control system controls the moving distance of the filter backflushing shaft (6) by setting the residence time.

2. The filtration system of claim 1, wherein: the at least two second filters are arranged on different branches and are respectively connected with the second booster pump (12) through multi-way valves.

3. The filtration system of claim 1, wherein: the outside of the cylindrical barrel body (5) is provided with a jacket, and the temperature of the jacket is 250-270 ℃.

4. The filtration system of claim 1, wherein: a discharge pipe (511) is arranged at the melt inlet (51) of the second filter.

5. The filtration system of claim 1, wherein: an exhaust port (521) is arranged at the melt outlet (52) of the second filter.

6. The filtration system of claim 1, wherein: the filtering precision of the first filter is 20-60 micrometers; the second filter has a filtration accuracy of 20-40 microns.

7. The filtration system of claim 1, wherein: the ratio of the number of the transverse recoil channels (61) to the number of the melt channels (74) is less than or equal to 10 percent.

8. A process for operating the filtration system of claim 1, comprising the steps of:

5) When the pressure difference value of the pressure sensors at the two sides of the second filter is ultrahigh, the second filter starts back flushing, the central control system controls the discharge valve to be opened, the back flushing shaft of the filter automatically moves downwards, the transverse back flushing channels are communicated with the melt flow channels one by one, the melt back flushing filter screen (4) enters the back flushing shaft (2) of the filter through the transverse back flushing channels (21) and is discharged, and the control unit adjusts the first booster pump and the second booster pump to synchronously increase flux;