WO1985004340A1

WO1985004340A1 - Plane filter

Info

Publication number: WO1985004340A1
Application number: PCT/FI1985/000032
Authority: WO
Inventors: Aarne ELLILÄ
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-04-02
Filing date: 1985-03-29
Publication date: 1985-10-10
Anticipated expiration: 1986-10-02
Also published as: FI69250B; FI841314A0; JPH0246243B2; FI69250C; BR8507175A; JPS61500954A

Abstract

A plane filter which comprises a filter cloth (8) which is from the periphery towards the center at a small angle in relation to the horizontal plane, means (4) for directing the water to be filtered from the periphery onto the filter cloth (8), and a spray pipe (9, 10) rotating below the filter cloth, the pipe being fitted to spray water through the filter cloth in order to detach the dirt which has adhered to it and to transport it over the lower edge of the filter cloth into a drain well (6) located in the center of the filter. In order to increase the capacity of the filter there are, placed on top of the filter colth (8), baffles which slow down the flow of the water and increase the thickness of the water layer. The baffles may be rings (11) placed on top of a circular filter cloth (8) and concentric with it, or a net (13) placed on top of the filter cloth.

Description

Plane filter

The present invention relates to a plane filter which comprises a filter cloth which is inclined from the periphery towards the center, means for directing the water being filtered from the periphery onto the filter cloth, and a spray pipe rotating below the filter cloth, the pipe being fitted to spray water through the filter cloth in order to detach the dirt adhering to the cloth and for transporting it over the lower edge of the filter cloth into a drain well situated in the center part of the filter.

I

There are two possibilities for transporting away the dirt left on the filter cloth. According to one alternative, water to be filtered is directed onto the cloth in such an amount that it flows continuously over the lower edge of the filter cloth into the drain well, at the same time transporting with it the separated dirt. According to the other alternative, the dirt is detached and transported from the filter cloth over the lower edge of the filter cloth by means of appropriately directed water sprays, without there being a great overflow of the water being filtered.

Of the alternatives presented, the former is possible only when the water to be filtered is available in a larger quantity than required by the permeability of the filter, and when the use of an excess of water can be permitted. In the filtering of the industrial process waters this is not, however, permissible, since the filtration is carried out in order to recover heat and to reduce the effluent load. For this reason, only the latter one is practicable. The flow rate of water through the filter cloth is dependent on the mesh size of the filter cloth, on the proportion of the mesh area to the total surface area of the filter cloth, and on the thickness of the water layer on top of the filter cloth. The flow of water onto the filter cloth, and thereby the thickness of the water layer on it, can be increased only to the extent that all the water has time to filter through the filter cloth without a wasted flow over the lower edge. Of course, the finer the mesh of the filter cloth, the more effective the filtration is, but at the same time water flows more slowly, throughthe filter cloth and the capacity of the filter is lower.

The object of the present invention is to provide a plane filter of the type mentioned in the beginning, the filter having, in spite of using a fine-mesh filter cloth, a capacity sufficient for practical purposes. According to the invention, this has been achieved by placing on top of the filter cloth baffles which slow down the flow of the water being filtered and increase the thickness of the water layer.

According to one embodiment of the invention, in a circular plane filter the baffles are made up of several rings concentric with and separate from the filter cloth and fitted at suitable intervals, the rings being fastened to the upper end of the filter cloth to prevent them from moving. In this case the rings are preferably a few millimeters high, and they can be located at intervals of about 5-10 cm.

According to another embodiment of the invention, the baffles are made up of a net, or two or several nets one on top of another, placed loosely on top of the filter cloth, the net or nets being fastened to the upper end of the filter cloth to prevent it/them from moving. The net is preferably woven from a thread a few millimeters thick, and a suitable mesh size may be about 2 x 2 - 10 x 10 cm. When two or several nets are used one on top of another, they have preferably different mesh sizes.

The invention is described below in greater detail with reference to the accompanying drawing. In the drawing.

Figure 1 depicts diagrammatically a vertical section acros the plane filter,

Figure 2 depicts a top view of a plane filter according to one embodiment of the invention, and

Figure 3 depicts in a similar way another embodiment.

The plane filter according to the invention comprises a vessel 1, which is preferably circular and is divided by means of ring-like partitions 2 and 3 into three compartments, i.e. an outermost annular compartment 4 for the water to be filtered, an intermediate annular compartment 5 for the filtered water, and an innermost cylindrical compartment, i.e. the drain well 6. The water to be filtered is directed from the pipe 7 into the outermost annular compartment 4. On top of the intermediate annular compartment 5 there is a filter cloth 8, which is supported in a suitable manner so that it is inclined inwards at a small angle in relation to the horizontal level. Below the filter cloth 8 there is a rotating pipe 9, from which there branch out spray pipes 10, which are fitted to spray water through the filter cloth in order to detach the dirt accumulated on it from the filtered water, and for conveying the dirt over the inner edge of the filter cloth into the drain well 6, from which it is removed together with the rinsing water via a drain pipe not depicted. The filtered water is directed from the compartment 5 via a pipe not shown, to the point of use in question.

The water to be filtered flows from the annular compartment 4 onto the filter cloth 8, the feed rate being adjusted so that all the water passes through the filter cloth before reaching the lower inner edge of the filter cloth. In order to increase the capacity of a filter equipped with a fine-mesh filter cloth, according to the invention there are baffles placed on top of the filter cloth to slow down the flow and to increase the thickness of the water layer. According to the embodiment depicted in Figure 2, these baffles comprise rings 11, concentric with the filter cloth and placed loosely on top of the filter cloth 8, the rings being made of, for example, light plastic strips 2-4 mm tnick and 2-10 mm high. Only some of the threads are shown in the figure. The rings 11 can be placed at interval of 5-50 cm, for example, and by means of threads 12 running radially at suitable intervals they are fastened to the outer edge of the filter cloth in such a way that they remain in place in spite of the flow of water. Owing to the rings, the water being filtered is dammed behind the rings in such a way that its flow rate decreases and the thickness of the water layer on top of the filter cloth increases, and consequently, water also better passes through the fine-mesh filter cloth and the capacity of the filter respectively increases. However, owing to their light weight the rings 11 do not prevent the water sprays coming from the spray pipe 9 from detaching the dirt and from conveying it towards the lower edge of the filter cloth 8 and over the edge into the drain well 6.

Figure 2 shows a very simple alternative according to the invention. In this embodiment there is a net 13 placed loosely on top of the filter cloth 8, only part of the net being shown in the figure. The net has been woven from a resilient and light thread a few millimeters, for example 2-4 mm, thick. The mesh size of the net may be, for exampl about 2 x 2 - 10 x 10 cm. The net is secured by any suitab method to the upper edge of the filter cloth 8 in such a way that it remains in place. The net 13 produces a dammin effect similar to that produced by the rings 11 described above, and therefore the capacity of the plane filter equipped with a fine-mesh filter cloth increases considerably. Practical experiments have shown that, when t mesh of the filter cloth is 65 μm, a net of this kind, having a mesh of 5 x 5 cm, approximately triples the capacity of the filter. By using two nets, one on top of the other, the mesh size of the lower net being 3 x 3 cm and the mesh size of the upper net being 6 x 6 cm, good results were obtained with a filter cloth having an even smaller mesh size, i.e. 45 ym.

Claims

—C—la—im—s

1. A plane filter comprising a filter cloth (8) which is inclined from the periphery towards the center, means (4) for directing the water to be filtered from the periphery onto the filter cloth, and a spray pipe (9, 10) rotating under the filter cloth, the pipe being fitted to spray water through the filter cloth in order to detach the dirt which has adhered to the cloth and to transport it over the lower edge of the filter cloth into a drain well (6) located in the center part of the filter, c h a r a c t e r i z e d i n that on top of the filter^' cloth there are placed baffles which slow down the flow of the water being filtered and increase the thickness of the

/ water layer.

2. A filter according to Claim 1, the filter being circular, c h a r a c t e r i z e d i n that the baffles are made up of several rings (11) , concentric with and separate from the filter cloth (8) and fitted at suitable intervals, the rings being fastened (12) to the upper end of the filter cloth to prevent them from moving.

3. A filter according to Claim 2, c h a r a c t e r i z e i n that the rings (11) are a few millimeters high.

4. A filter according to Claim 2 or 3, c h a r a c t e r i z e d i n that the rings (11) are located at intervals of about 5-50 cm.

5. A filter according to Claim 1, c h a r a c t e r i z e i n that the baffles are made up of a net (13) , or two or several nets (13) one on top of another, placed loosely on top of the filter cloth (8) , the net or the nets being fastened to the upper end of the filter cloth to prevent them from moving.

6. A filter according to Claim 5, c h a r a c t e r i z i n that the net or the nets (13) are woven from a thread a few millimeters thick.

7. A filter according to Claim 5 or 6, c h a r a c t e r i z e d i n that the mesh size of the net or nets (13) is about 2 x 2 - 10 x 10 cm.

8. A filter according to Claim 5, 6 or 7, c h a r a c t e r i z e d i n that when two or several nets are used one on top of another they have the same mesh size or different mesh sizes.