FI67180C - METHOD FOER TILLVERKNING AV MICROPOROES FILTER PLATE ANVAEND APARAT SAMT MICROPOROES FILTER PLATE - Google Patents

Description

'67180

Method for producing a microporous filter plate, the apparatus used in the method and the microporous filter plate Method for the preparation of a microporous filter plate, including apparatus for a microporous filter plate

The invention relates to a method for producing ceramic microporous filter tiles from ceramic raw material pulp using an extrusion process, in which method, after said extrusion step, the tile web or tile blanks are dried and, after drying, fired.

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The invention also relates to an extrusion device for use in the manufacture of microporous ceramic filter plates, comprising a raw material tank or similar raw material supply devices.

The invention further relates to a ceramic microporous filter plate.

Large-scale microporous tiles are required for various filtration tasks, so that in addition to the properties of the tiles, the economics of their manufacture are of considerable importance.

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The present starting point has been the method of drying a web mill such as paper, a powder such as peat, a solid such as wood, a porous material and the filter plates required in connection with the applicant's FI patent No. 61,739 (cf. U.S. Pat. No. 4,357,758). . Em. according to the method of the patent-20, the object to be dried is brought into hydraulic contact with the liquid under reduced pressure relative to the object to be dried via a fine-pore liquid-filled suction surface.

It is an object of the present invention to provide the preferred above-mentioned fine porous liquid impregnation surface. One application of the filter tiles according to the invention is precisely the drying of peat by the method according to the above-mentioned FT patent No. 61 739, in which case very large areas are required.

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2,67180 filter plates. However, the present invention is not intended to be limited only to filter plates used in connection with the method according to FI Patent No. 61,739, but the invention is generally suitable for use in connection with filtration in a wide variety of applications.

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Em. Common applications of FI patent No. 61,739 and this invention in the paper industry include sludge drying. One of the conventional filtration applications according to the invention in the paper industry is the filtration of process water with the aim of returning as much process water as possible to the circulation and thus reducing the use of raw water by up to 50%.

One area of application of the filter plates according to the invention is the purification of raw water as well as the purification and flue gas recovery of flue gases.

In each of these different applications, different size distributions of the micropore diameter of the tiles may be required, but these properties can also be controlled within the scope of the invention.

It is already known to produce filter plates by a mold casting method, 20 but this method is expensive and slow and requires various manufacturing steps "if it is desired to obtain internal cavities in the filter plates" through which a vacuum is applied to the plates.

It is also known to use an extrusion process for the production of ceramic products, but not for the production of filter tiles. This is because filter plates require a thin and wide plate shape, which shape has been impossible to extrude evenly without the inventive insight set forth below.

It is an object of the invention to provide a filter plate and a method of manufacturing the same which provides an even higher permeability to the filter plates. It is a further object to provide a method and a filter plate and a device for producing filter plates which enable the production of uniform filter plates, in particular of uniform strength, and which filter plates can advantageously also be provided with the above-mentioned 3 67180 cavities, which increase the effective surface area of filter plates.

In order to achieve the above objects and to avoid the above-mentioned disadvantages, the method according to the invention is mainly characterized in that the ratio of the length measured in the direction transverse to the direction of the extruded nozzle orifice to the nozzle width in the thickness direction L / H>

The filter plate according to the invention is mainly characterized in that said plate has internal cavities which are intended to be connected to a device for maintaining a vacuum and that the plate is plate-like and the ratio of plate width to plate thickness is L / H> 20.

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In the experiments leading to the present invention, it was surprisingly found that the extrusion method is suitable for the production of filter plates, provided that the L / H ratio is sufficiently high, according to experiments performed at least 20. If the ratio is lower, the 20 nozzle edge already disturbs clay mass flow and uniform flow to achieve, which is an absolute prerequisite for the production of stress-free intact tiles, is very difficult regardless of how the mouthpiece is shaped. As a concrete example, miniature sets of filter plates having a thickness of 8-10 mm and a width of 200 mm and 630 mm have been produced by the above principle and by the method described in more detail below.

In the following, the invention will be described in detail with reference to some embodiments of the invention shown in the figures of the accompanying drawing, to which the invention is not limited.

Figure 1 shows the microstructure of the main component of the filter material raw material according to the invention, i.e. kaolin.

Figure 2 shows the nozzle of an extrusion device according to the invention as seen from the inlet side of its extrusion material.

35 4 67180 IS ..

Figure 3 shows the same as Figure 2 seen from the opposite direction.

Figure 4 shows a section 1V-IV in Figure 5A.

Figure 5A shows an alternative section V-V in Figure 2.

Fig. 5B shows, in a manner similar to Fig. 5A, another alternative embodiment of the compression nozzle.

Figure 6A illustrates an erroneous flow profile of the material to be extruded avoided in the present invention by the compression nozzle.

Figure 6B illustrates the correct flow profile of the extrusion die according to Figure 6A, respectively.

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Figure 7 shows a preferred humidity-temperature curve of a tunnel-dryer for tiles according to the invention as a function of travel in a tunnel.

Figure 8 illustrates the combustion curve of the combustion of filter plates 20 according to the invention in an electric furnace.

Figure 9 shows a cross-section of a preferred slab according to the invention. Figure 9 is at the same time a section 1X-IX in Figure 10.

Figure 10 shows a filter device consisting of a series of filter plates according to the invention, the plates of which are connected at their open end to a special suction foot.

The main steps in the manufacture of the micro-30 porous filter plates 10 according to the invention, shown in cross-section in Figure 9, are as follows: 1. Preparation and homogenization of the raw material.

2. Slab formation by extrusion method.

3. Drying.

35 4. Burning.

5,67180

The main component of the raw material of the filter plates according to the invention is preferably kaolin, the microstructure of which is shown in Figure 1. The kaolin particles K are flat and hexagonal in shape. Due to their electrical charges (+, -), the particles K tend to form a "card-5 house structure" that is highly porous. Such a structure is formed in an aqueous suspension, and when water is removed the porous structure shrinks strongly. In order to prevent shrinkage, according to the invention, finely divided Al (OH) particles are added to the raw material, which support the kaolin structure. In the combustion step, Al (OH) 2 decomposes according to formula 10 below into Al 2 O 2 and water, resulting in higher porosity.

2 A1 (0H3> · + Al2O3 + 3 H2O ΔΗ = 300 kJ / mol Al ^ This reaction takes place at a temperature of about 300 ° C and binds a considerable amount of heat.

At the end of the firing of the slabs 10, when the sintering point of the material mixture begins to approach, the pores of the slab 10 tend to close. In this case, the pores no longer form uniform channels and this fact 20 impairs the permeability of the plate 10. In order to prevent the harmful phenomenon mentioned in the present invention, calcium carbonate (CaCO 3) is added to the raw material, which decomposes during the firing step of the tiles 10 and at high temperature (> 1200 ° C) into calcium oxide and carbon dioxide as follows: CaCO 3 + CaO + CO 2 The plasticity of the pulp is an important property in the extrusion step to be described in more detail later. Without plasticizers, the flow properties of the pulp are poor and the raw material has poor raw strength. As is known, the so-called ball-clay, but the plasticity it gives is not always sufficient. Another more advantageous alternative is to add concrete to the raw material mass for said purpose.

35 Example 1

A ceramic mass having the following composition has been developed for use in the invention: I: 6 671 80 TABLE 1 substance content by weight% 5-- kaolin 45 aluminum hydroxide 30 spherical clay 20 chalk 5 10 __

In addition to the mentioned substances, about 20% of water is mixed into the pulp.

The following table shows the properties of the different raw materials: 15 TABLE 2 substance quality manufacturer particle size 20 ------- * kaolin E ECC International> 2 and 25% | > 10 ym 25%> 53 ym 0.05% 25 aluminum OL-104 Martinswerk hydroxide spherical clay Hyplas-64 ECC International <5 ym 85% <2 ym 75% 30 <1 ym 62% <0.5 ym 52% chalk QM-25> 53 ym 0.01%> 20 ym 6% 35> 10 ym 19%> 5 μη 39% <2 ym 39% 7 67180

Figures 2-5 show an extrusion die structure for forming a continuous web of the raw material described above, which web, either as a continuous strip or cut into filter plates, is transferred to drying and then to incineration, the latter two steps being described in more detail later.

Figures 2-5 show two alternative implementations of the extrusion nozzle. According to the figures, the extrusion die 20 comprises a cylindrical body plate 21 screwed to the wall of a container (not shown) having the raw material mass described above, from which the slab web W (Figures 6A and 6B) is extruded through the nozzle slot 25 of the die 20. Figures 6A and 6B illustrate the effect of the flow profile VJ of the pulp web discharged from the die 20 on the success of the extrusion. Fig. 6A shows a case where only an equal-width plate orifice is used without the arrangements according to the present invention, where the flow velocity profile of the web to be extruded from the mass M is as shown in Fig. 6A, i.e. the velocity is lower in the edge regions than in the middle. In this case, the web either breaks or, due to speed differences, internal stresses are generated in it, which break the tiles 20 at the latest during the drying stage. According to Fig. 6B, the nozzle 20 is provided with a special lip 22; 22A, 22B described below in connection with Figs. 2-5, so that the flow profile P £ of the web to be extruded through the nozzle 20 is sufficiently uniform over the entire width of the web.

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According to Figures 2-5, the extrusion nozzle of the extrusion nozzle 20 comprises a lip piece 22 to be fixed to the body plate 21 by screws 24, in the region of which the portion 25 ”of the nozzle gap 25 is flat. The portion 25 'of the nozzle slot 25 in the region of the body plate 20 is best seen in Figures 3 and 4. The slot portion 25' is at its widest in its edge areas on the rear surface of the body plate 20 (Figure 3). In its central region, the slit 25 ’tapers at an angle (Fig. 4). The maximum width of the gap 25 'is denoted by H 2 in Fig. 4. The dimension prevails along the length L1 of the edge region of the gap 25 ', after which it tapers along the length to a uniform width 1 ^ which prevails along the length L ^ 35. In Fig. 4, the angle of convergence prevailing in the region is indicated by the reference α 2 · Correspondingly, the length of the nozzle gap 25 '+ 2x (Lj + L, 2)

The nozzle slot 25 is provided with a lip plate 26 attached to the body plate 20 on the side inlet side of the pulp 20. Of the plate 26, two different embodiments are shown in Figures 5A and 5B. As shown in Figure 5A, the plate 26A comprises a canister-like portion having elongate grooves 28 in the flow direction of the pulp and spikes 29 therebetween which provide the cavities 11 of the filter plate 10 (Figure 9). According to Fig. 5A, the leading edge 30A of the plate 26A 10 as well as the lip 22A is wider from its central region than from the edge regions, and thus the length of the lip in the mass flow direction is greatest in the middle of the nozzle gap 25 and gradually tapers toward the edges.

Thus, the lip 22A brakes more in the center of the nozzle gap 25, where the flow rate would otherwise be at its maximum as shown in Figure 6A. As shown in Figure 5B 15, the leading edge 30B of the plate 26A as well as the lip 22B is substantially arcuate. Fig. 5A shows the maximum length and the minimum corresponding length Sq of the constant plate (Hq) portion 25 "of the lip 22A. In Fig. 5B, respectively, the minimum length of the lip 22B is denoted by S 1 and the maximum length by S 1, between the lengths of which the lip length profile 30B

20 changes substantially in the form of a circular arc. In practical experiments, it has been found that the lip 22A shown in Figure 5A works best when the moisture content of the raw material mass is about 21%. The lip 22B shown in Figure 5B, on the other hand, works best when the humidity is about 19%. In this case, the dimensions of the plates made with the nozzles 20A and 20B were L = 220 mm, 25 P = 220 mm, H = 9 mm (Figs. 9 and 10).

An extrusion nozzle such as that described above is preferably capable of producing an internally unstressed web of material W 1 which is plate-like. According to the invention, the length of the nozzle slit is the ratio of the width of said slit 30 to L ^ / H ^> 20. Most preferably said ratio L ^ / H ^ is in the range 20 ... 40.

Before the extruded tiles 10 can be fired, they must be allowed to dry slowly and evenly. The drying step is best accomplished in a room 35 in which the humidity and temperature of the air are adjustable. Drying occurs more evenly at high temperatures due to the lower viscosity of the water. In this case, the humidity of the air must be high so that the surface does not dry too quickly. When the material to be dried has reached its maximum temperature, drying can take place at a lower humidity, as water now moves to the surface of the tile 10 at a higher speed. Figure 7 shows a preferred humidity-temperature curve of a tunnel dryer used in the invention as a function of tile travel.

The firing of the tiles after drying is carried out, for example, in an electric oven, the preferred burning curve (temperature / burning time) of which is shown in Figure 8.

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Figure 9 shows a preferred embodiment of a slab 10 according to the invention. According to Fig. 9, the width of the slab is denoted by L, the thickness of the slab by H and the length of the slab by P (Fig. 10). The plate 10 has cavities 11 between which the widths of the bases are preferably of the same order of magnitude as the widths of the cavities 11. The dimension of the cavities 11 in the thickness direction H is preferably about 10 ... 50%, preferably about 25 ... 35% of the thickness H. The length P of the slabs 10 is e.g. of the same order as the width L. Such a slab has advantageous properties for the uses indicated. Typically, the width of the tiles is 20 L «.200 mm ... 1000 mm and the thickness H« 5 mm ... 15 mm, preferably about 7 ... 10 mm. The tiles 10 at the lower end of said dimensional ranges are suitable for filtering various sludges, while the larger tiles 10 are suitable for use in e.g. the paper industry and peat drying.

The cavities 11 of the plate-like plate 10 shown in Figure 9 extend over substantially the entire length of the plate and between the cavities 11 there are bases 14 which are preferably substantially as wide or slightly narrower than the width of the cavities 11.

Within the scope of the invention, the shape of the tiles 10 according to the invention and their cavities 11 can vary widely and differ, for example, from that shown in Figure 9 only by way of example. The plate 10 can be e.g. corrugated. The cavities 11 may be round, polygonal, etc. In general, the dimensions, shapes and distribution of the cavities 11 and the cavities of the supports between the cavities 11 are chosen so as to give the plates 10 maximum mechanical strength in view of the high differential pressures on the outer surface of the plates 10 between.

Fig. 10 shows an example of a filter unit 30 assembled from slabs 10 according to the invention, comprising e.g. a plastic foot 20 with grooves 21 of width L in the slabs, into which the ends 13 of the slabs 10 with open cavities 11 fit with sufficient compressive strength and tightness. The opposite ends 12 of the tiles 10 are closed with glue or a suitable mass. Closing can also take place after the extrusion step by pressing the cavities 11 at one end 12 of the slabs in a special work step. Channels 22 open into the grooves 21, which in turn lead to channels 23 parallel to the plane of the foot 20. Through said channels 23, the foot 20 and the filter unit 15 30 communicate with a suction pipe 24 connected to a suction device (not shown) known per se.

When using the filter units 30 according to Fig. 10, e.g. for drying peat, the feet 20 are connected to a conveyor belt, by means of which the filter units 30 pass through a basin with a peat-water suspension. As a result of the suction effect, a layer of peat accumulates on the surface of the tiles 10, which is in hydraulic contact with water under reduced pressure, and the peat dries efficiently with the flow of said conveyor outside the sludge basin. At a suitable stage, the peat dried with special brush members and / or scrapers is removed from the surface of the tiles 10.

The fine pore radii of the microporous tiles 10 according to the invention are mainly in the range of 0.05 to 2 [mu] m, when the tiles are intended in the process according to the aforementioned FI patent No. 61,739 (cf. U.S. Patent No. 4,357,758). use.

The tiles 10 according to the invention can be manufactured with a mechanical structure such that they can withstand even the high pressures prevailing in the application, which are typically of the order of 10 bar. Em. The most important properties of the tiles used in the water suction drying according to FI patent 35 No. 61 739 are their permeability to water (w) and the discharge pressure of the micro-capillaries to air (ΔΡ). The permeability 11 67180 of the slabs 10 can be measured e.g. by providing the slab 10 with a plastic foot 20 as shown in Fig. 10 with a water space 23 connecting all the cavities 11 of the slab 10. The other ends 12 of the slab 10 are closed. The plate 10 is placed in a pool of water and water is sucked through it. The amount of water-5 V flowing through the plate 10 during t is measured and the permeability-ti can be calculated from the formula

V

W = ‘10 where A = effective area of the slab.

The above-mentioned microcapillary discharge pressure ΔΡ, which is an essential factor in water-suction drying, can be measured with the same device as the permeability. In the ΔΡ: η measurement, pressure-15 air is supplied to the plate 10 so that the pressure is gradually increased until the air begins to pass through the plate 10. The pressure prevailing in the plate when the first air bubbles are detected is the ΔΡ value of that plate 10. One example of the measured permeability of a slab prepared as described above is the value w = 0.072 mm / s with a pressure difference of 1 bar. Then the ΔΡ value of the roainit-20 tu of the slab was ΔΡ = 1.8 bar. A tile made according to the invention having these values is well suited for use in water suction drying according to FI patent No. 61,739.

The following are claims within the scope of which the various details of the invention may vary.

Claims (11)

1. A method for the production of microporous filter plates (10) from ceramic material mass using nozzle extrusion, which method is applied to the web (W (25) has a ratio of median width (Lq) and height (Hq) LoyHo> 20 in the thickness direction of the web (W W) which is measured perpendicular to the path direction of the extruded web (W gang). 10 2. A method according to claim 1, characterized in that in the process an extrusion nozzle (20) is used, which is designed in such a way that the flow velocity profile (P2) in the width direction (L) of the material web (V) to be produced is from the nozzle (20) substantially smooth. 3. A process according to claim 1 or 2, characterized in that the composition of the ceramic raw material used in the method is essentially the following: Kaolin about 45v-Z aluminum hydroxide about 30v-Z clay or the equivalent of about 20v-Z krlta or the equivalent of about 5v-Z 25 4. A process according to claim 3, characterized in that about 20 weight-Z water is also mixed in said material mass. 5. A nozzle extruder used for the purpose of milling corrosive ceramic filter plates, comprising a borehole container or equivalent feedstock, characterized in that the nozzle extruder (25) of the nozzle (25) of the nozzle (25) of the nozzle (25) of the nozzle seen perpendicular to the thread direction of the web (U U) to be produced, and that in connection with said nozzle (20) there is a particular lip construction (22; 22A; 22B), being length (S) in the web of material (W )) outflow direction is greater at the center region of the web (W ^) than in the edge regions of said web (W ^) in a way that said lip construction (22; 22A; 22B) slows more on the center region of the web (W ^) than the edge areas and in this way a substantially uniform velocity profile (P 2) of the web (W Arrangement according to claim 5, characterized in that in connection with the lip structure (22; 22A; 22B) in the middle of the mouth of the nozzle (25) there is a disc-shaped and cam-shaped disc portion (26; 26A, 26B) which has material flow-directed elongated grooves. (28) and between these cam-shaped tags (29), with which halides (11) are provided in said path, which are parallel to its outflow direction. 15 Device according to claim 5 or 6, characterized in that the mouth of the extruder nozzle has an initial portion (25 ') which tapers in the direction of flow of the pulp at appropriate angles (α α, ο ^ »0) and that after this tapered portion (25'). *) follows a planar 20 (L, H) portion (25 "), whose length (S) in the outflow direction of the pulp is also greatest (S () in the center regions of the orifice (25) and that said length (S) decreases (S ^) continuously (Fig. 5B) or stepwise (Fig. 5A) at the edges of the orifice. 8. Ceramic microporous filter plate, characterized in that said plate (10) has internal cavities (11) which are intended to be connected to a source of suppression or the like and that the plate (10) is disc-shaped and the ratio between the width (L) and thickness (H) L / H> 20. 9. A filter plate according to claim 8, characterized in that the plate has several, most preferably at least five or more parallel oblong slides (11) next to each other, between which are provided (14) and which slides extend continuously along the substantially full length of the plate (P). . 10. Ceramic plate according to claim 8 or 9, characterized in that the diameters of the fine pores in the microporous plate (10)