A rotating disc filter means

IS 2 199 248 T3

DESCRIPTION

Filter media with rotating discs.

The present invention relates to a rotary filter having several filter discs arranged on a rotor. More precisely, the filter is constructed so that the liquid mixture to be filtered is supplied by a hollow shaft of the rotor into the interior of the filter discs, each filter disc being composed of two side walls with filter media and a wall arranged around it. of the periphery, preferably also equipped with filtration means.

In filtration, the liquid passes through the filter media from the inside to the outside, whereby a filter layer composed of solid particles, a coarse phase, is formed inside the filter media. The filtration takes place with the help of a hydrostatic overpressure which is achieved because the level of the liquid of the liquid mixture inside the rotor is set higher than the level of the liquid of the filtrate outside the filter discs. Such a disc filter is described, for example, in US-A-3 163 601.

The problem with filters that have an inside-out flow direction through the filter media is that a large part of the filter layer falls off during rotation and falls back into the reservoir, or reservoir, when said layer rises above the surface of the tank of unfiltered liquid mixture. This results in a higher concentration in the inlet liquid mixture and thereby deteriorates the technical performance of the filter, that is, its capacity in various aspects, such as the hydraulic capacity, the amount of solid particles separated and / or the purity of the filtrate.

The object of the present invention is to increase the capacity of the filter. It follows that, for a given inflow, a smaller filter area is needed and therefore smaller filter sets are required.

According to the present invention, in the interior space of the filter discs there are elements that carry the filtered coarse phase, as well as obstruction or interception means that prevent said coarse phase from falling back into the inlet liquid mixture tank. . These blocking means are hereinafter called barrier elements. The filter capacity is increased by preventing the coarse phase from being filtered again and thereby occupying the filter area.

A filter according to the present invention is well suited to waste water purification, raw or raw water purification, also called return water in the paper industry, and fiber recovery in the paper industry. In the present claims 1 and 2 a rotary disk filter according to the present invention is defined.

The invention is described in more detail below and with reference to the accompanying drawings, in which:

figure 1 shows a cross section (II in figure 2) of a filter, figure 2 shows a longitudinal section (II-II in figure 1), figure 3 shows the invention in a sector of a filter disk, the Figure 4 shows an alternative embodiment of the invention, Figure 5 shows a lateral surface of a filter disc in a cross-sectional view (VV in Figure 6), Figure 6 shows, on an enlarged scale, a section (VI-VI in figure 5) of the side surface, figure 7 shows an alternative embodiment of the invention, figure 8 shows a modification of the embodiment of figure 7.

Figures 1 and 2 show a main embodiment of a disk filter. This filter comprises a filter rotor 1 located inside a filter container 2 for filtering. With the aid of drive means 5, a hollow shaft 3 on which filter discs 4 with filter media are arranged are rotated in the container. In its simplest embodiment, the filter media is composed of a filter cloth supported on a lower support layer, so that an interior space 6 is formed. The filter cloth is attached to the two faces of the filter discs and, preferably also to the outer periphery 7. The inside of the filter or filter discs communicates with the hollow shaft 3. The liquid mixture to be filtered is introduced into the hollow shaft through the inlet 8 and thus also into the interior space 6 of the filter discs. According to a known technique, means, not shown, are responsible for maintaining a substantially constant level on the shaft and within the filter discs. An advantageous arrangement for this purpose can be an automatic speed control, so that the speed increases when the level tends to rise and vice versa. The filtrate is drawn through an outlet 9. The height difference between the inlet and the outlet is a measure of the effective hydrostatic pressure. The completely filtered coarse phase is transferred, according to the invention, to a collecting container 10 inside the hollow shaft. The lower part of this stationary collecting container is inclined towards an outlet 11 of the coarse phase. The coarse phase that has not yet come loose or fallen off the filter cloth during the rotation of the filter media is washed away with the aid of spray nozzles 12 arranged on the outer sides. Part of the water spray thus passes through the filter cloth and cleans it, whereby the coarse phase falls into the collecting container 10.

Figure 3 shows in cross section a quarter sector of a filter disc 4 of an embodiment according to the invention. The inner space of the filter discs is provided with plates, here called carrier elements 13, which protrude from the hollow shaft 3. The plates extend towards the periphery and are arranged between the sides of the filter discs in an axial direction. The extension is such that a gap 14, an opening, is left next to the periphery. The purpose of this opening is that the liquid mixture can flow backwards, in the opposite direction to rotation, during the movement of the carrier elements in the liquid mixture. Another function that is possible, thanks to these separations, is the rapid extraction of air from the cells formed by the carrier elements when they are submerged back into the liquid reservoir, as well as the rapid supply of air under the carrier elements when they come out of the tank surface. The carrier elements are oriented such that they assume a substantially horizontal position during the passage of the liquid level upward out of the bath.

IS 2 199 248 T3

A slight downward inclination in the gap 14 facilitates a return flow of the liquid mixture to the reservoir in the passage of the liquid surface, but said inclination should not be so great that any phase of coarse that has been detached also slides downwards. inside the tank. The level of the liquid mixture should suitably be kept higher than the center of rotation so that an effective filtering surface area that is as large as possible can be achieved. The carrier elements 13 are thus oriented so that the inner ends thereof which are adjacent to the axis are advanced during the rotation with respect to the outer ends.

In a preferred embodiment according to the invention, between each pair of carrier elements 13, one or more shorter outer carrier elements 15 are arranged near the periphery. Whereby the number of the largest carrier elements 13 can be kept low. Furthermore, these outer carrier elements 15 are suitably arranged so that on leaving the liquid reservoir they assume a substantially horizontal position, with a slight outward inclination. For these carrier elements there must also be a gap 16 at the periphery for the discharge of the unfiltered liquid mixture and for the outlet of the air, respectively.

According to the present invention, it is not possible that a coarse phase 22 which has been released from the filtration media can fall back into the liquid mixture. This risk exists from the moment the vane leaves the liquid reservoir until the coarse phase can slide into the collecting container 10. To this end, obstruction or interception means are provided, here called barrier elements 17, so that the thick phase cannot slide off the blades during the rotation before reaching the edge of the collecting container 10. Said barrier elements can be arranged in the innermost part of the vanes and extend forward in the direction of rotation, that is, they can have an upward bend when viewed from the side where the filter disc has a direction of movement of runs upwards, in the direction of rotation or according to the inner edges of the blades. The amplitude of the angle of the elbow up must be such that the part bent upwards, the barrier element, in the rotation exceeds a horizontal position only after the edge of the collecting container has passed, after which the coarse phase may slip inside the container. Advantageously, on the outer bearing elements of the periphery this bend must also be arranged upwards, of approximately the same size as that described above.

As seen in FIG. 4, the bulk phase barrier element 22 may alternatively be a plate 18, advantageously attached to the collecting container 10, or constitute one of the walls of the container. The plate extends in a circular arc from the surface of the tank, in the direction of rotation, so that the liquid mixture rises to the edge of the collecting container along all the filter discs. Unlike the barrier elements of the carrier elements described above, this plate is a stationary barrier element 18. This barrier element must be positioned so that the inner edges of the carrier elements slide very close to the barrier element. Also according to this embodiment, the carrier elements can be constructed with the previously described barrier elements 17 as additional security against any fall into the liquid bulk phase mixture through the gap between the stationary barrier element 18 and the carrier elements. .

As is evident from Figures 5 and 6, in certain applications carrier elements 19 may be arranged on the sides of the filter discs, here called side carrier elements. Advantageously, these elements are given a radial extension which corresponds to the extension in radial direction of the filter means and can be, for example, flat bars or a grid. The dimensions of these side plates are such that they transport at least the thick phase 22, which is detached from the sides, up to a height where the subsequent interior bearing elements (13 in Figure 3) with their barrier elements have time to reach by rotation above the surface of the tank of the liquid mixture. The barrier elements 17 are therefore in charge of transporting the coarse phase to the collecting container 10, which falls on the blades 13 by subsequent rotation to this position. Said side carrier elements 19 can advantageously be arranged so that they are support elements of the filtration means, generally the filter cloth.

By creating the barrier elements, a greater flow of liquid mixture is obtained through the gap 14 (Figure 3) between the carrier element and the periphery, compared to that which would be obtained without barrier elements. This has been shown to cause certain disturbances at higher rotational speeds. The liquid mixture flowing back through gap 14 detaches the filter layer, the coarse phase, over a distance. Consequently, this reduces both the purity of the filtrate and the filtering capacity which concerns the amount of coarse phase.

This problem is solved, as seen in Figures 7 and 8, with a shield or shield member 20 radially external to the carrier element 13 towards the periphery. This shield is supposed to protect the bulk phase layer 22 outside the carrier from the liquid stream by directing the stream from the periphery. Shield 20 may be curved or may have a straight shape as shown in Figure 7. An advantageous design is an angled plate 21 (figure 8), which gives more resistance and prevents the thick phase from passing through the gap. This design thus decreases the need or the number of outer carrier elements 15. It has been shown that the combination of barrier elements with shield members on the outside of the inner carrier element 13 allows the filters to operate at a substantially rotational speed. higher. This means that, for a given inflow of the liquid mixture, the size of the filter equipment can be substantially reduced.

Various modifications can be made within the scope of the invention. In certain applications it may be advantageous, from an economic point of view, to eliminate filter media extending around the periphery of the filter discs. In these cases, neither the outer carrier elements 15 nor the shield members 20, 21 are needed.