Back-wash filtering device for filtering high viscosity liquids.

0001The invention relates to a backwashable filter device for filtering a highly viscous liquid with a housing which has an inlet opening for the liquid to be filtered, a filter and an outlet opening for filtrate.

0002A number of backwashable filter devices are known in the literature. US Pat. No. 3,574,509 describes a controllable filter for filtering a liquid. The filter element consists of two concentrically perforated cylinders that hold a very fine wire mesh located between them, this structure being supported in a hollow body. A backwash arm rotates around an axis in the middle of the filter element. The backwash arm has a slot which is defined by molded parts which sealingly sweep over the inner periphery of the filter element. The residue that accumulates during filtration is flushed back through the slit in the arm.

0003A backwashable filter system is known from EP-A - 0 305 606, a wave-shaped arrangement being installed in the storage space of a filter basin in such a way that, with a partially opened sludge water flap, there is a direct outflow of the fluidized granular filter material in the sludge water outlet - and thus the loss Filter material - prevented.

0004The backwash filter according to DE-A 37 05 803 has a filter chamber in which a cylindrical filter insert is inserted, through which the medium to be filtered flows from the inside to the outside. This filter insert has an inner cage, the cylindrical wall of which has essentially horizontally extending, slot-like windows which are separated from one another by webs, and in the interior of which an axially movable slide which removes the filter residues is arranged.

0005EP-A-0 411 163 describes a filter device with continuous cleaning of the filter surface. The device contains a cylindrical housing with an inlet opening and an outlet opening. A sleeve with a filtering side surface and an internal cavity serves as the filter element. A scraper element is connected to a drive and mounted in an annular space which is formed between the inner surface of the housing and the filtering outer surface of the sleeve. The scraper element is designed in the form of at least one spiral band which encompasses the sleeve and interacts with the filter surface thereof.

0006Also known from EP-A - 0 305 575 is a backwashable filter apparatus with mechanical removal of the filter cake.

0007The object of the invention is to provide a filter device which can be fully backwashed without mechanical backwashing aids, ie that the filter residue can be removed practically completely from the filter without moving parts such as scrapers or backwashing arms. The mechanical backwashing aids mentioned are subject to wear, making it necessary to replace the relevant parts. In addition, mechanical, moving parts are prone to repair. Both lead to filter devices being disassembled or at least having to be handled inside. These operations are particularly complex when a highly viscous liquid is filtered. If this medium is also harmful to health, special safety precautions are necessary, which makes repairs even more complex.

0008The backwashable filter device according to the invention for the filtration of a highly viscous liquid has a housing which has an inlet opening for the liquid to be filtered, a filter and an outlet opening for filtrate and is characterized in that<ul id="ul0001" list-style="dash"><li>the filter with its side facing the liquid to be filtered rests on a separating body with recesses (“reject spaces”),</li><li>the separating body has inlet channels for the liquid to be filtered, the inlet channels opening into the recesses,</li><li>the separating body has a drain device for the backwashed liquid that is spatially separated from the inlet channels,</li><li>the housing has a drain for the backwashed liquid and that</li><li>the inlet opening and the drain are designed to be closable.</li></ul>

0009The separating body serves to largely separate the liquid to be filtered from the backwashed liquid. During backwashing, the residue removed from the filter ("reject") first reaches the recesses, which are referred to below as "reject spaces" due to their function and via the drainage device, which is spatially separated from the inlet ducts, to a drain that is best attached to the filter housing. Channels can also be provided as the drain device, which lead from the reject spaces through the separating body to the drain. As a drainage device, however, a system of grooves is also conceivable which extend along the surface of the separating body facing the filter and thus discharge the backwashed liquid laterally to the outside.

0010It has been shown that the filter device according to the invention is fully backwashable, that is to say that by backwashing the filtrate, the residues deposited in the filter can be lifted off the filter virtually completely and rinsed out, provided the backwashing liquid has a viscosity of at least 0.4 Pa.s . The filter device according to the invention works without moving internal parts due to the separating body. The filtration and backwashing processes are only controlled by means of pump and shut-off devices. Furthermore, no filter drive is required.

0011The filter device according to the invention is particularly suitable for the filtration of highly viscous cellulose solutions, polyacrylic solutions, polyester solutions and - since it is completely closed and can be used as a so-called "inline filter device" - for the filtration of highly viscous aggressive, abrasive and harmful solutions. The device according to the invention does not require a dynamic external seal.

0012The filter device according to the invention also allows internal flushing with chemical solvents.

0013The effect according to the invention is independent of the filter material used, so that the appropriate filter can be used for the liquid to be filtered in each case. A restriction to certain filter materials is therefore not necessary. Common filter materials are, for example, metal fiber nonwovens, sintered fabrics, combinations of metal fiber nonwovens with fabrics and plastic mesh.

0014The geometric shape of the ray spaces is also largely irrelevant for achieving the effect. However, it is clear that the shape of the reject spaces should be designed in such a way that locations with low flow velocities are avoided. At these locations, the residues raised by the filter during the backwashing process are only made more difficult by the backwashing liquid or are only partially carried away. In contrast, hemispherical, dome-like or groove-shaped ray spaces are well suited, the inlet channels advantageously opening at the deepest point of the ray spaces. The radius of the reject spaces must of course be adapted to the filter material and the pressures that occur on the filter during backwashing in order to mechanically support the filter so that it does not tear. A mechanical support is of course also to be provided on the side of the filter facing the outlet opening in order to avoid tearing or deformation of the filter due to the high pressures required for the filtration. Such a support is provided, for example, by the filtrate plate described below, which has continuous channels for the passage of the filtrate.

0015For economic reasons, the reject spaces should be small so that the residues can be flushed out with as little liquid as possible. The precisely defined reject spaces also allow a precisely adjustable reject quantity without changing the quantity.

0016A preferred embodiment of the filter device according to the invention consists in that the drain device is designed as a channel-like system with drain channels and collecting channels.

0017In this embodiment, an efficient removal of the backwashed liquid from the reject spaces is realized. The drainage channels are short channels that connect the reject spaces with the longer collection channels. The drainage channels expediently have a smaller diameter than the collecting channels. The small diameter, together with the high viscosity of the liquid, prevents it from getting into the drain or Collecting channels, residue removed from the filter, during the subsequent filtration back into the reject spaces and thus again on the filter. It is furthermore expedient to design the inlet channels tapering at their mouth into the recesses.

0018The invention also relates to a separating body for use in the filter device according to the invention, which is designed as a plate ("separating plate") and is further characterized in that<ul id="ul0002" list-style="dash"><li>the axes of the inlet channels and the collecting channels are essentially normal to one another,</li><li>the recesses are hemispherical, dome-shaped or designed as grooves,</li><li>the mouths of the inlet channels are provided at the deepest point of the recesses, and</li><li>Lead at least two drainage channels from each recess to collecting channels.</li></ul>

0019The separating plate allows all functions necessary for loading and backwashing the filter material to be carried out. It has been shown that the pressure loss in the separating plate is negligible compared to the pressure loss of the filter material.

0020A preferred embodiment of this partition plate is that the inlet channels are tapered at the mouths and that the outlet channels have a smaller diameter than the collecting channels.

0021If the reject spaces of the partition plate according to the invention are provided in the manner of grooves, it has proven to be expedient to make the grooves between 1 and 5 mm wide and to arrange them in parallel.

0022The separation plate is best equipped with 15,000 to 25,000 inlet channels and 30,000 to 40,000 outlet channels per square meter.

0023The design of the separating body as a plate opens up the possibility of arranging several filters one above the other in a housing and thus increasing the filter area.

0024Such a variant of the filter device according to the invention now consists in that<ul id="ul0003" list-style="dash"><li>two separating plates are provided, each with an adjacent filter, the separating plates facing each other with the sides carrying the filters,</li><li>and that a filtrate plate is provided between the separating plates to support the filters and to remove the filtrate.</li></ul>

0025Any plate-shaped body which has sufficient flexural strength to support the filters during the filtration process and which has channels for removing the filtrate is generally suitable as the filtrate plate. Since in the described embodiment filtrate penetrates through channels into the filtrate plate both through the top and through the bottom side, longitudinal channels (eg in the form of bores), which run parallel to the top and bottom of the filtrate plate and are connected to the channels opening from the top and bottom, pick up the filtrate and discharge it laterally. The dimensioning of the filtrate plate, ie its thickness, the number of channels, etc. can be adapted to the respective purpose.

0026In order to avoid undesired mixing of the individual liquid media, the inflow of liquid to be filtered, the outflow of filtrate and the outflow of backwashed liquid must of course be spatially separated from one another, but this can be provided in a simple manner by a person skilled in the art.

0027The separating plates can be covered on the outside by inlet plates, which likewise have channels through which the liquid to be filtered is distributed or introduced into the inlet channels of the separating plates.

0028Another advantageous embodiment of the filter device according to the invention is constructed in a sandwich-like manner from a plurality of filter units, a filter unit consisting of an inlet plate and two separating plates, each with a filter, which are separated from one another by a filtrate plate.

0029For easier cleaning of individual filter devices, it has proven to be useful not to filter with a single device but with a filter system consisting of several filter devices which are connected in parallel.

0030The invention is explained in more detail below with reference to the drawing, which shows a plate-like configuration of the separating body 5 in FIG. 1 and a simple configuration of the filter device in FIG. FIG. 3 shows the operation of a filter system which consists of two filter devices connected in parallel.

00311a is a perspective, schematic representation of the separating body 5 designed as a plate. Reference numeral 7 stands for the inlet channels through which the liquid to be filtered passes to the recesses (“reject spaces”) 6 and subsequently through the filter (not shown), is pressed. 5a denotes that side of the separating plate 5 which faces the liquid to be filtered. The ray spaces 6 are located on the underside 5b of the partition plate 5. The collecting channels 8 'run through the entire partition plate 5 parallel to each other and parallel to the top and bottom 5a and 5b. The two collecting channels 8 ″, which collect the backwashed liquid flowing out of the collecting channels 8 ′ during backwashing, do not necessarily have to extend over the entire width of the separating plate. The bottom 5b - and thus the recesses 6 - are covered by the filter (not shown). The partition plate 5 according to the invention can have further collecting channels (not shown) in its interior, which discharge backwashed liquid from the outlet channels 8 in a different direction than shown in FIG. 1b.

0032FIG. 1b again shows the partition plate according to FIG. 1a for a better understanding of the channel-like system in the interior of the partition plate, but part of which has been cut out. You can see the reject spaces 6, which are dome-shaped. The inlet channels 7 are tapered at the mouth into the reject spaces 6. The diameter of the inlet channels is preferably between 1 and 6 mm. The diameters of the discharge channels 8 and the collecting channels 8 'are preferably between 1 and 5 or between 4 and 10 mm. The liquid backwashed through the filter into the reject spaces 6 flows from the reject spaces 6 through the drainage channels 8 into the collecting channels 8 'and 8' '. The partition plate 5 shown has two collecting channels 8 ″, which are located on two opposite sides of the partition plate 5.

0033Fig. 1c shows a section of the partition plate 5 and that along the line cc of Fig. 1a. In this illustration, only the collecting channels 8 ″ can be seen from the drain device for the backwashed liquid. The collecting channels 8 'were indicated by dashed lines; the drainage channels 8 are not visible in this illustration. The axes of the inlet channels 7 and the collecting channels 8 'are indicated by x and y; in the embodiment of the separating plate shown, the axes x and y are normal to one another.

0034The size of the separating plate depends on the pressure load inside the filter. In the case of a groove-like design of the reject spaces, with a groove width of 4 mm (with a distance between adjacent grooves of 1 mm) and with a separating plate size of approximately 250 x 1000 mm (the area available for the filter), there is a free filter area of ​​approximately 0.2 m². The partition plate can also be supported by a web or by support points in the middle of the plate.

0035In the following, some typical data are given for the embodiment of the separating plate shown in FIG. 1a, which is particularly suitable in a filter device for the filtration of highly viscous, spinnable cellulose solutions (eg NMMO solutions):<tables id="tabl0001" num="0001"><img file="EP0572369A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0572369A2_D0002.tif" /></tables>

0036FIG. 2 shows a section through a filter device according to the invention in a simple embodiment, the separating plate 5 being the one described in FIG. 1. 1 denotes the housing of the device, 2 and 4 stand for the inlet and outlet opening. The filter 3 rests on the separating plate 5 on the side which has the reject spaces 6.

0037The function of the filter device shown in Fig. 2 is as follows:

0038The highly viscous liquid to be filtered is conveyed by means of a pressure booster pump 10 with the valve 11 open and with the drain line 9 closed (closure not shown) through the inlet opening 2 under pressure on the separating plate 5. The partition plate 5 is shown in FIG. 2 in section along the line cc of FIG. The liquid penetrates through the inlet channels 7 into the reject spaces 6 and is pressed through the filter 3 with the deposition of the substances to be filtered off (residue). The filtrate passes through a filtrate plate 12, which has filtrate channels 13 and supports the filter 3, to the outlet opening 4 and can be obtained there.

0039For backwashing, the valve 11 is first closed, the discharge line 9 is opened and the filtrate is pressed under pressure (pressure generation not shown) through the outlet opening 4 and the filtrate plate 12 through the filter 3, the filtered off residue being lifted off. The residue collecting in the reject spaces 6 is subsequently determined by the (not visible in FIG. 2, in FIG. Drain channels 8 (shown in FIG. 1b) are rinsed into the collecting channels 8 'and 8' 'and can be removed via the discharge line 9 of the filter device.

0040In Figure 2, only the design features of the filter device necessary for understanding the invention were shown. It goes without saying that, for example, suitable holders for the individual plates are provided in the housing and that the plates must be sealed off from one another in order to avoid undesired mixing of the individual liquids.

0041FIG. 3 shows a variant of the filter system according to the invention consisting of two filter devices A and B according to the invention connected in parallel with filters 3 of the same size. The filter devices are only shown schematically, since their mode of operation has already been explained with reference to FIGS. 1 and 2. Reference numerals A and B stand for each of the described embodiments.

0042Both filter units are initially charged with liquid to be filtered by means of the booster pump 10 when the valves 11 and 11 'are open. The valve 11 '' is open for filtration, the discharge valves 11 '' 'and 11' '' 'are closed. During the filtration, a pressure difference is built up between inlet and outlet openings 2 and 4.

0043To backwash the filter device B, the valves 11 'and 11' 'are closed and the drain valve 11' '' is opened. As a result, filtrate flows from filter device A in the opposite direction through filter device B and thereby rinses the filter 3 located in B. The filtrate loaded with residue is pressed out of the filter device B through the opened discharge line 9.

0044To backwash the filter device A, the valves 11 and 11 '' are closed and the drain valve 11 '' '' is opened. As a result, filtrate flows from filter device B in the opposite direction through filter device A and thereby flushes the filter 3 located in A. The filtrate loaded with residue is pressed out of the filter device A through the opened discharge line 9 '.

0045The filtrate delivery rate required for backwashing can be conveniently adjusted via the booster pump 10 and thus be adapted exactly to the respective conditions. By increasing the speed of the pump 10, a higher backwashing capacity can be set, whereby a better cleaning of the filter is achieved.

0046According to the invention, more filter devices can also be connected in parallel to form a filter system, as a result of which even higher backwashing performance can be achieved.