FI117273B - Filter plate, method of making the filter plate and filter apparatus - Google Patents

Description

117273

FILTER PLATE, METHOD FOR MANUFACTURING THE FILTER PLATE AND FILTER DEVICE

FIELD OF THE INVENTION

5

The invention relates to a suction filter plate for forming a cake in a filtering process. The plate can be used as an element, in particular, in a filter disk to be rotated in slurry.

BACKGROUND OF THE INVENTION

The filter disc apparatus comprises filter discs, the inside of which is connected to the radial suction lines leading to the suction device. The wafers are rotated in slurry a Italy so that the lower wafers are on the I slide. The egg 15 forms a cake on the surfaces of the discs. When the cake is rolled up from the slurry, the cake is removed. One disc consists of a plurality of sector-shaped filter plates.

. . In the Kapi Haarinen action filter disc apparatus, the filter disk becomes saturated with the disk

* * I

20 absorbent fluid. This principle is described, for example, in Fl-C-77161 (corresponding to WO-88/00742). Such devices have also been on the market (Ceramec® filters by Outokumpu Corporation, Finland).

• · ♦ · · »i · • · •. · **. Capillary filter plates can be made of a suitable ceramic or * * * 25 polymeric material. The disc usually comprises a porous support layer and •; ·; filtering surfaces on the support layer. For example, U.S. Pat. No. 4,863,656, U.S. Pat. No. 1,498,159 and WO-02/055178 disclose such plates having ceramic filter surfaces.

• I * · ♦ · «· • · • · Φ /. 30 The surface of the sludge in the basin is below the axis of rotation of the discs.

• * ·

The filter periphery is thus longer in the slurry than the inner periphery. Thus, the cake becomes ** thicker on the outer periphery assuming that the permeability of the filter media 117273 is radially uniform. The solids content of the slurry increases towards the bottom of the basin, which further increases the uneven cake formation. This effect is particularly noticeable in the case of heavy minerals such as iron ore, chromium ore and lead concentrate. 5 As a result of the formation of an uneven cake, the cake on the filter surfaces has a wedge-shaped cross-section.

In addition, the characteristics of the cake vary with thickness. In particular, the moisture content of the cake increases as the thickness increases. The uneven properties cause problems in the further stages of the process. Especially the difference in humidity can cause problems. This is important for filtering materials that are difficult to achieve.

Uneven moisture content can cause downstream problems, for example in pelleting processes. In addition, moisture can cause problems, such as freezing, during storage and transport. Many materials have a transport moisture limit. If heat drying is available, excess moisture can be removed in this way, but of course the cost will increase. Therefore, it is often necessary to use a smaller filter device. . • · · * 11 * '20 This will reduce the capacity of the appliance.

• »t Ψ 9 9 99 9 9

To solve the problem of uneven cake formation • *; v. WO-02/45815 discloses a filter plate consisting of at least «· · ··· two separate filter portions having different filtering properties.

• «• · 9 25

:. ·. SUMMARY OF THE INVENTION

··· · · · · · 99: · [A filter plate according to claim 1 has now been invented. In others • ♦ ·. * ··. The claims disclose some advantageous embodiments of the invention.

• 99 9 9 9 9 9 «9 9 9 9 • β · 3 117273

According to the invention, the permeability of the filter disk is continuously decreasing towards the outer edge. This results in a cake with a more uniform thickness and thus more uniform properties.

Preferably, the thickness of the filtering layer increases towards the outer edge of the sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are part of the written description of the invention. Other examples of the invention are illustrated in the drawings.

Fig. T shows a disk filter device viewed from the end of the rotor.

Fig. 2 is a radial cross-section of a filter plate that can be used, for example, in the apparatus of Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

.. According to the invention, the disadvantages associated with uneven cake formation can be eliminated by means of a filter plate having a continuously decreasing «« 4 '! permeability in the radial direction, i.e., permeability decreases towards the periphery. In this way, the cross sectional profile of the filter cake is corrected, and * * • v. the result is a cake of even thickness.

• 4 «1« 9 9 9 999 25 The required difference in permeability can be achieved, for example, by the following means: 4 «· 999 9: ***: - The thickness of the filter layer of the filter medium increases towards the periphery.

9 99; * [- The pore size of the filter medium filter layer decreases towards the outer periphery.

• · ·. ···. - The porosity of the filter layer in the filter medium decreases towards the periphery.

• 9 Λ 30 You can also combine these modes.

9 9 9 9 9 9 9 9 9 9 9 9 9 9 99 9 9 4 117273

The main advantage of the invention is that the properties of the cake formed in the filtration, especially the moisture, are uniform. Thus, for example, a filtration device with maximum capacity can be used. More consistent material is easier to handle further, for example by washing the cake or pelleting. 5 Even humidity is important for storage and transportation. Additionally, when the cake is uniform, the cake will load the filter plate more evenly.

When there are no discrete areas on the surface of the sheet (such as the sheet of WO-02/45815), fabrication is easier. When the filter layer is uniform 10 (i.e. non-bonded), the risk of leakage is reduced.

The principle of the invention can be used, for example, in - capillary filters - conventional vacuum disk filters 15 - pressurized disk filters - leaf filters.

Materials that can be used to provide a non-uniform filter material are, for example: • I · * 11 20 - sintered or silicate-bonded ceramic materials such as Al 2 O 3, SiC, TrO 2, • · ** V ZrO 2, corundum, etc., or combinations thereof - , such as polypropylene, polyethylene, m 9: v. polyamide, fluorine resin, etc., or combinations thereof t »! ···. sintered or molded plastic materials such as polypropylene, polyethylene, 25 polyamide, fluoroplastics, etc., or combinations thereof:. - metallic filter cloth materials such as stainless steel, titanium, nickel • · 9, etc. or combinations thereof * m 9 - sintered metallic filter materials such as stainless steel, titanium, nickel • t ·! ···. etc. or combinations thereof • # f 30 - carbon based materials such as graphite, amorphous carbon etc. or their I /! combinations.

«1« 117273 5

Preferably, the filter sheet comprises an inner layer on which the filter layer is affixed. The inner layer supports the filter layer. Preferably, a filter layer is provided on both sides of the inner layer. The inner layer is preferably porous so that the filtrate moves from the filter layer to the inner layer, from where it is collected.

The (radial) ceramic plate may, for example, have a length of 200 to 800 mm and a width of, for example, 200 to 600 mm. The thickness of the entire sheet may be, for example, 20 to 80 mm, and the thickness of the filter layer may be, for example, 0.1 to 10 mm. As the thickness of the 10 filter layers increases from the inner periphery to the outer periphery, the thickness may be, for example, 0.1 to 1 mm on the inner periphery and 0.2 to 2 mm on the outer circumference.

As the pore size of the filter medium decreases towards the periphery, the permeability decreases accordingly. The pore size may, for example, be about 1 µm on the inner ring and 0.5 to 0.8 µm on the outer ring, for example. The porosity is substantially constant.

As the porosity of the filter medium decreases toward the outer periphery, the porosity may, for example, be about 40% by volume on the inner periphery and about 30% by volume on the outer periphery.

• · i .ν '. 20 • · 9 • »

The filter web, which increases in thickness towards the outer periphery, may conveniently be * • 1 «prepared by dipping the inner layer substrate outer peripheral f ··; to the material layer forming the filter layer. Vacuum, • *: ***: Due to adhesive, electrostatic, or magnetic forces, the material forming the 25 filters adheres as a layer to the inner layer substrate; *: The surface where the substrate is purchased from the blend naturally forms a layer whose thickness increases from the top to the bottom. This treatment «S \. repeated as necessary to achieve the desired thickness. In addition, the difference in thickness between the upper edge and the lower edge can be controlled by dipping speed. : V; 30 The lower the speed of the substrate in the vertical direction, the greater the difference in * ψ; \ j thickness. After the dipping step, the filter layer is usually cured * · to form the final filter layer. The edges of the sheet are usually covered with a suitable impermeable layer, for example by glazing or coating.

A suitable ceramic filter plate for use in a capillary filtration dryer according to the invention has a microporous surface layer having a pore size of less than 5 µm, preferably 0.2-3 µηι, and this microporous surface layer is supported by the porous inner layer. The inner layer has means for removing fluid from the top layer. These means preferably comprise at least one recess. The filter plate is further provided with a fitting member 10 which is secured to the inner periphery.

In the manufacture of a ceramic filter plate, an inner layer is formed of at least one substrate. The substrate is preferably in the form of a powdered ceramic material such as alumina, silicon carbide, titanium oxide, zirconia, corundum or silica. In addition, the substrate may be metal or an alloy, polymer or graphite. In a preferred embodiment, the ceramic material is mixed with the binder and the liquid so that the resulting ceramic mixture is suitable for further processing. The ceramic alloy is first placed in the mold so that the mold is partially filled with the ceramic alloy. Then, t * # V; "20 is mounted on the surface of the ceramic mixture in the mold for at least one desired recess area. After compression, the raw material is sintered over a temperature range of 1150 - 1550 ° C. «·: ***: corresponding recesses. Alternatively, the substrate can be made from parts,

• M

·! which have been treated separately as described above. After sintering • «* *. ···, combine the parts into complete filter elements.

• · 30 • · * • «9

After the sintering step, the substrate is coated with at least one microporous layer. Preferably, the coating process is performed by dipping the substrate downward into a bath of microporous layer forming material. In this way, the desired surface layer is naturally produced, the thickness of which increases towards the periphery. Furthermore, the coating process can be carried out, for example, by spraying or by strip molding ceramic microporous layer material on the surface of the substrate, but in this case, special means are required to achieve the required radially variable permeability. The microporous layer-forming material may additionally be metal or metal alloy, polymer or graphite.

After the coating process, the substrate is sintered with microporous ceramic layer forming materials at a temperature in the range of 1150 to 1550 ° C. If an additional ceramic layer is required, the coating and sintering process are repeated. Furthermore, sintering can be carried out in one step 15 on a substrate having a plurality of microporous layers. After sintering the microporous layer, the filter element is substantially monolithic having a hierarchical structure, and the filter element is then ready for mechanical treatment. This means that the filter element is drilled if no hole or holes have been formed for the fitting part during the pre-forming step * · f 20 so that it is possible to install «· * 'on the filter plate; the fitting.

• * · «·« ·

The filter device of Figure 1 comprises a drum 1 provided with a plurality of * *! ···. with filter discs consisting of sector filter plates 2. The inside of each plate 25 is led by a radial suction tube 3. The respective plates in the various disks: the tubes are connected to a special filtration line which may be connected to • M t ····· through a distribution valve and line 4, 5 or 6 to a vacuum source as well as through line 7 to the overpressure source during the cleaning step, * 30 mm The wheels are rotated in a tank 8 to which slurry is fed through line 9. When

»9 I

I I I

the plates are subjected to vacuum, suction fluid through the plates 2, and a cake containing the # # solids and liquid is formed on the surfaces of the plates. When the plate rises from 8 117273 slurries, a negative pressure is maintained, whereby more liquid is sucked in and the cake continues to dry. Before the final drying, the washing liquid may be sprayed onto the cake, in particular to remove salts from the cake. Clean water can be used as the washing liquid. After drying, the cakes are removed by scrapers 10. The removed dry cake 11 drops through the troughs at the front of the basin onto the conveyor 12. During the removal step, the plates are briefly subjected to liquid overpressure 7 to clean the plates. The filtrate and possibly some additional liquid may be used as a cleaning agent. After the cleaning step, the plates are again subjected to vacuum and a new cake forming step begins. The various steps 10 are marked outside the periphery of the apparatus of Fig. 1 as follows: cake forming step 13, cake washing step 14, drying step 15, cake removing and plate cleaning step 16. If the cake is not washed as a filter, the drying step consists of steps 14 and 15.

15 The auxiliary pressure lines 4, 5 and 6 lead to a filtrate tank 17, in which a vacuum 18 is formed by pump 18. The filtrate is removed from the tank via line 19 by a pump 20 via a valve 24. Some of the filtrate is supplied as a washing liquid to the washing line through valve 21 and pressure control valve 23. In addition, special washer fluid may be introduced from the tank 25 to the washing line by pump 22 via valve 28.

• * * 'f;' 20 Alternatively, external water may be used for washing and pumped by · · * Y through line 30.

· «·« E · «i« «; v. The bottom of the pool 8 has a cradle-type mixer 26. The pool can be emptied i * I ···. through the bottom valve 27. There are 29 ultrasonic vibrators inside the pool. They are used from time to time for a more thorough cleaning of the plates. For ultrasonic treatment:; \ the tank is emptied and filled with the desired cleaning fluid.

· ** · «* • · •« «

The plate 2 of Figure 2 comprises a porous inner layer 31 and a microporous * * ·! · * ·. on both sides and at the edges of the inner layer of the filtering layer 32.

Λ 30 The inner layer comprises at least one radial recess 33, which starts at the inner edge of the plate. In this case, the inner edge is provided with a fitting part • · »♦« 117273 9 34 with a connector 35, but the plate can also be fitted in place without such a special part.

The thickness of the filtration layer 32 on the sides of the plate 2 increases continuously from the inner edge 36 to the outer edge 37. Thus, a cake of uniform thickness is formed on the surfaces of the plate in the filtration process.

* · • · · 1 · * 1 • · • 1 · ii · fr fr • • fr fr fr 4 «« «* • fr fr« «fr fr« fr fr «fr fr fr · fr ea • # »··· · · · * · af fr · ·« 9 «fr fr • · · fr fr fr 1 • fr 9 · fr fr1 fr fr fr fr fr fr fr fr fr a • · 1 «« a • 1

Claims (12)

A filter plate (2) comprising a filter layer (32) having a fluid permeability, the filter layer comprising an inner ring (36) and a 5 outer ring (37), characterized in that the permeability of the filter layer (32) is continuously reduced by the outer ring (36). 37) places. The filter plate (2) according to claim t, wherein: - the thickness of the filter layer (32) increases continuously with the periphery (36) towards the periphery (37), or - the pore size of the filter layer (32) decreases continuously with the periphery (37), or - the porosity of the filter layer (32) is continuously reduced towards the inner periphery (36) towards the outer periphery (37). 15 A filter plate (2) according to claim 1 or 2, comprising an inner layer (31). The filter plate (2) according to claim 3, wherein the inner layer (31) is * · *, porous. «« «* · Ft ·» • · · p The filter plate (2) according to claim 3 or 4, wherein the inner layer:. (31) both surfaces have a filter layer (32). * · • »• · The filter plate (2) according to any one of the preceding claims, wherein the filter layer (32) is made of ceramic material. «· · •« * · ··· A method of making a filter plate (2) comprising an inner layer: ***; (31) and on both sides thereof a filter layer (32) having a permeability. X 30 for liquid, wherein the filter layer comprises an inner periphery (36) and an outer periphery (37), # · * * .... characterized in that a substrate 117273 forming an inner layer (31) is produced and a filter layer is continuously adhered to the outer periphery (36). (37) towards the surface of the inner layer. The method of claim 7, wherein 5 filter layers (32) are applied to both surfaces of the inner layer (31). A method according to claim 8, wherein, in the manufacture of the filter layer (32), the outer periphery of the substrate of the shape of the inner layer (31) is dipped downward from and upwardly from the material of which the filter layer is formed. Filter device, characterized in that the device has at least one filter plate (2) comprising a filter layer (32) having a liquid permeability, the filter layer comprising an inner periphery (36) and an outer periphery (37) such that the filter layer (32) has a permeability. continuously decreasing from the inner ring (36) to the outer ring (37). Filter device according to claim 10, characterized in that at least one filter plate (2) of the device Ve is made up of an inner layer (31) and a filter layer (32) on both sides thereof, is * * the permeability of the liquid, wherein the filter layer comprises an inner peripheral (36) and a * * * * outer peripheral (37) such that a f * is formed to form the inner layer (31); substrate and attaching a filter layer whose permeability decreases continuously from the inner periphery (36) towards the outer periphery (37) to the surface of the inner layer. • I »25 A filter device according to claim 10, characterized in that the device · [[[·] is a vacuum disk filter device, a pressurized disk filter device, a silicon disc filter device or a leaf filter device. • · · • · • · ♦ • <«* * · • ψψ ♦ • · 117273