EP0809528A1

EP0809528A1 - Apparatus for filtering liquids

Info

Publication number: EP0809528A1
Application number: EP96903296A
Authority: EP
Inventors: Rune H. Frykhult
Original assignee: Ingenjorsfirman R Frykhult AB
Current assignee: Ingenjorsfirman R Frykhult AB
Priority date: 1995-02-13
Filing date: 1996-02-09
Publication date: 1997-12-03
Also published as: AU4734896A; CA2212946A1; WO1996025218A1; FI973307A0; SE9500502D0; FI973307L

Abstract

An apparatus for filtering liquids has a vat (2) in which a hollow filter body (1) having an operative horizontal extension is arranged. There is provided an inlet means which comprises a portion of the vat wall forming at least one passage (11) for the liquid to be filtered, and a deflecting means (13) positioned in the vat between said portion of the vat wall and the filter body and adapted to deflect liquid flowing into the vat through said passage, such that the liquid reaches the filter body substantially evenly distributed along said operative horizontal extension thereof.

Description

Apparatus for filtering liquids

The present invention relates to an apparatus for filtering liquids, such as fibre pulp suspension or polluted water.

A common type of such a filtering apparatus includes a vat having a wall, and a hollow filter body having an operative horizontal extension and positioned in the vat. There are inlet means for supplying the liquid to be filtered into the vat outside the filter body, coarse fraction outlet means for discharging developed coarse fraction from the apparatus, and fine fraction outlet means for discharging developed fine fraction from the interior of the hollow filter body.

In this type of filtering apparatus the inlet means conventionally includes a trough located outside the vat and extending along said operative horizontal extension of the filter body. The liguid to be filtered is initially supplied to this inlet trough and is distributed from the trough across a we r to the vat whereby the liquid is more or less evenly spread in the vat along the operative horizontal extension of the filter body. This inlet trough usually has a considerable long outer wall which is exposed to a relatively strong pressure exerted by the liquid in the trough. In consequence said long wall of the trough has to be thick enough or be provided with reinforcements to withstand the liquid pressure. Therefore, such a conventional inlet trough s relatively expensive and adds significantly to the cost of the filtering apparatus.

The conventional inlet trough also suffers from other dis¬ advantages. Firstly, the liquid to be filtered is often unevenly distributed along the operative horizontal extension of the filter body, l. e. the liquid flow toward the filter body is larger in the middle of the filter body than at the ends of the filter body. Secondly, when filtering fibre pulp suspensions fibres tend to build up sediment in the trough. Thirdly, the liquid flowing across the weir into the vat can create a lot of foam, which disturbs the filtering process. Forthly, the long inlet trough outside the vat takes up a lof of space.

An object of the present invention is to provide a filtering apparatus having a less expensive inlet means, as compared with the conventional apparatus.

Another object of the present invention is to provide a filtering apparatus which has a superior performance to the conventional apparatus in the sense that the incoming liquid is evenly distributed along the operative horizontal extension of the filter body, the build-up of sediment is counteracted, and foam creation is reduced.

Yet another obiect of the present invention is to provide a filtering apparatus which takes up less space than the conventional apparatus.

These objects are fulfilled by means of a filtering apparatus of the common type described above characterized in that the inlet means comprises a portion of the vat wall forming at least one passage for the liquid to be filtered extending from outside the vat to the interior thereof, and deflecting means positioned in the vat between said portion of the vat wall and the filter body and adapted to deflect liquid flowing into the vat through said passage, such that the liquid reaches the filter body substantially evenly distri¬ buted along said operative horizontal extension thereof. Thus, a conventional inlet trough is not necessary and can be eliminated which substantially reduces the fabrication cost of the apparatus.

According to a preferred embodiment of the invention, the deflecting means comprises a partition wall dividing the interior of the vat into a first compartment, into which said passage opens, and a second compartment, in which the filter body is situated. The partition wall makes it possible in a easy way to deflect incoming liquid upwardly or downwardly or both ways. If the liquid is to be deflected upwardly, the partition wall and the vat can define at least one upper opening situated above said passage. If the liquid is to be deflected downwardly the partition wall and the vat can define at least one lower opening situated below said passage. If desired the liquid can be deflected into two part streams, one flowing upwardly and the other flowing down¬ wardly, by providing both the upper and lower openings.

According to an embodiment of the invention, the deflecting means comprises a flow control means for controlling the liquid flow through said upper opening or said lower opening or both openings. If the flow control means controls the liquid flow through said lower opening, the velocity of the downwardly flowing liquid can be controlled so that sedimentation on the bottom of the vat is avoided.

The invention is explained below in more detail by way of example with reference to the accompanying drawings in which

Figure 1 is a side view, partly sectioned , of a prior art apparatus,

Figure 2 is a side view, partly sectioned, of an apparatus of the invention,

Figures 3 to 6 are parts of sectional views of different embodiments of the apparatus according to the invention, Figures 7 and 8 are sectional views taken along lines VII-VII and VIII-VIII, respectively, of Figure 6,

Figure 9 is part of a control valve,

Figure 10 is a modification of the control valve shown in

Figure 9, and Figures 11 to 13 are parts of sectional views of different embodiments of a control valve for the apparatus of the invention. In Fig. 1 there is shown a conventional rotary disc filtering apparatus including a plurality of coaxial hollow discs 1 having side walls of filter material, the discs 1 forming a row having an operative axial extension, and a vat 2 in which the discs 1 are arranged rotatable about a horizontal axis 3. There is inlet means for the liquid to be filtered including a trough 4 which is arranged outside the vat 2 and which extends axially along the discs 1. Liquid supplied to the trough 4 flows across a weir 5 into the vat 2. Coarse fraction developed on the side walls of the discs 1 is discharged by an outlet means 6 and fine fraction developed within the hollow discs 1 is discharged by a fine fraction outlet means 7. The discs 1 are rotated about said horizontal axis 3 by a drive motor 8. The vat 2 is provided with two outer elongated beams 9 supported by plinths 10.

Fig. 2 shows an apparatus of the invention which is similar to the conventional disc filtering apparatus of Fig 1, except that the inlet means for the liquid to be filtered is different. Thus, the inlet means of the apparatus of Fig. 2 comprises a portion of the wall of the vat 2 forming a plurality of passages extending from outside the vat 2 to the interior thereof. The passages 11 communicate with the interior of a horizontal pipe 12 through corresponding holes on the pipe 12. The inlet means furter comprises deflecting means, which in this case takes the form of a partition wall 13 positioned in the vat 2 between said portion of the vat wall and the discs 1 and adapted to deflect liquid flowing into the vat 2 through the passages 11, such that the liquid reaches the filter discs 1 substantially evenly distributed along the operative axial extension of the row of discs 1. The partition wall 13 divides the interior of the vat 2 into a first compartment 14, into which the passages 11 opens and a second compartment 15, in which the discs 1 are situated. The passages 11 are dimensioned such that the flows of liquid through the respective passage--; 11 are substantially equal. With reference to Fig. 3, the partition wall 13 and the vat 2 define an upper opening 16 situated above the passages 11 and a lower opening 17 situated below the passages 11. As a result a first part stream and a second part stream, respectively, of the liquid flowing into compartment 14 is deflected upwardly through the upper opening 16 and down¬ wardly through said lower opening 17, respectively, into compartment 15. The upper opening 16 is located such that the liquid level in compartment 15 is well above the partition wall 13, whereby creation of foam is counteracted as said first part stream of liquid flows from compartment 14 to compartment 15. Since the liquid pressure on the partition wall 13 is insignificantly stronger in compartment 14 than in compartment 15, the partition wall 13 can be made designed a wall thickness which is considerably smaller than that of the inlet trough of the conventional apparatus.

In Fig.4 there is shown an alternative embodiment in which only an upper opening 18 is provided and a partition wall 19 is designed to form an upwardly converging flow area toward a level between the passage 11 and the opening 18. From said level the flow area diverges toward the opening 18. The upwardly converging part 20 of the compartment 14a creates a liquid flow resistance resulting in an even distribution of the liquid flow along the operative axial extension of the row of discs 1. The diverging part 21 of the compartment 14a has the effect of a diffusor resluting in a regain of the liquid pressure energy that was lost in the converging part of the compartment 14a.

To achieve a desired distribution effect, the velocity of the liquid flow past the narrowest part of the compartment 14a has to be relatively high (for example 5 metre/second). When starting up the apparatus, said high velocity of the liquid flow has the consequence that liquid can be flushed up above the surface level 22 of the liquid in the vat 2. This liquid flush is eliminated by providing a guide wall 23 above the upper opening 18, the guide wall 23 suitably being designated to direct the liquid flow downwardly into the vat 2.

If there is a risk for particle sedimentation in the vat 2, a number of lower openings 24 may be provided in the partition wall 14a. In case the apparatus only has a few discs 1, only one passage 11 through the vat wall may be necessary.

Fig. 5 shows another alternative embodiment m which the partition wall 13b only defines a lower opening 25. This embodiment is preferred when a maximal downwardly directed liquid flow is required to avoid sedimentation.

In Fig. 6 there is shown an embodiment similar tc that of Fig. 3 in which an upper control valve 26 is provided to control the sizes of the liquid flows through the upper opening 16 and the lower opening 17. The control valve 26 comprises a horizontal, turnable angle bar 27 having an axial extension which corresponds to the distance between opposite wall portions of the vat 2. The angle bar 27 has two pivot arms 28 which are journal led in bearings 28a on the vat 2. The angle bar 27 is pivotable by a lever 29 which is lockable by a locking means 29a in desired positions, whereby the through flow area m the direction upwardly m the com¬ partment 14 past the angle bar 27 is adjustable.

A lower control valve 30 (Figs. 6 and 11), which m principle is designed similar to the upper control valve 26, i.e comprising an angle bar 31, pivot arms 32, bearings 33, a lever 34 and a locking means 35. Thus, upon turning of the angle bar 31 by means of the lever 34, the through flow area in the direction downwardly in the compartment 14 past the angle bar 31 is adjusted. The adjustment of the angle bar 31 affects the sizes of the upper and lower liquid flows in the compartment 14 and enables a control of the flow velocity downwardly into compartment 15. Fig. 10 shows an alternative embodiment of the angle bar. In this case the angle bar 36 comprises a number of recesses 37,38, which are passed by the liquid flow.

In Figs. 8 and 12 there is shown an elongated guide plate 39 above the upper control valve 26. (Alternatively, the guide plate 39 may be positioned below the control valve 26.) The guide plate 39 guides the liquid flow to avoid flushing above the surface 40 of the liquid in the vat 2. (In certain applications it may be suitable to supplement with the guide wall 23 shown in Fig. 4.). The liquid flowing upwardly from the compartment 14 flows further across a weir 41 and the surface 42 of the liquid in the vat 2 is situated below the weir 41 (Fig.6 ) .

To eliminate the risk of liquid flowing across the weir 41 and affecting the discs 1 such that parts of the fibre mats on the discs 1 are flushed away, guide plates 43 are provided for guiding the liquid flow to avoid hitting the discs 1. The guide plates 43, suitably having U-cross-section, are positioned above the weir 41 and has an axial extension which is larger than the breadth of a disc 1.

In case the hollow filter body takes the shape of a rotary drum, it is preferable to use the guide wall 23 shown in Fig. 4. In such a case the guide wall 23 also serves to prevent the upper liquid flow from flushing away parts of the mat of fibres on the drum.

The embodiment shown in Fig. 13 is similar to that of Figs. 6 and 12, except that the controllable through flow area is provided between the vat 2 and the angle bar 44. A further controllable flow restricting passage 45 is provided between the angle bar 44 and an axial guide wall 46 on the vat 2. (The same effect is also achievable with the embodiment according to Fig.12, in which a further flow restricting passage 47 occurs between angle bar 27 and the guide plate 39.)

As a price-worthy alternative, one of the two hollow beams 9 may also be utilized as a part of the liquid inlet means. Such an alternative is shown in Fig. 6 and comprises a hollow beam 48 which is provided with an inlet member 49 and a number of passages 50 through the wall of the vat 2. In this case the beam 48 also serves as an reinforcement of the wall of the vat 2.

Many combinations of the embodiments described above are concievable. For example the guide plate 23 may be combined with the embodiments shown in Fig. 3 and 6. In practice only one of the two control valves 26 and 30 may be used and possibly in combination with the partition wall 19. In some applications the two embodiments according to Figs. 4 and 5 may be installed in the same vat. In such a case the liquid distribution can be controlled by valves outside the vat.

In the embodiments of the invention shown in the drawings, the liquid inlet means is provided at the descending side of the discs while the outlet means for discharging developed coarse fraction is provided at the ascending side of the disc. As an alternative, both the liquid inlet means and the coarse fraction outlet means may be provided at the ascending side of the discs.

Claims

1. An apparatus for filtering liquids, such as fibre pulp suspensions or polluted water, including a vat having a wall, a hollow filter body having an operative horizontal extension and positioned in the vat, inlet means for supplying the liquid to be filtered into the vat outside the filter body, coarse fraction outlet means for discharging developed coarse fraction from the apparatus, and fine fraction outlet means for discharging developed fine fraction from the interior of the hollow filter body, characterized in that

- the inlet means comprises a portion of the vat wall forming at least one passage for the liquid to be filtered extending from outside the vat to the interior thereof, and

- deflecting means positioned in the vat between said portion of the vat wall and the filter body and adapted to deflect liquid flowing into the vat through said passage, such that the liquid reaches the filter body substantional ly evenly distributed along said operative horizontal extension thereof.

2. An apparatus according to claim 1, wherein the deflecting means comprises a partition wall dividing the interior of the vat into a first compartment, into which said passage opens, and a second compartment, in which the filter body is situated.

3. An apparatus according to claim 2, wherein the partition wall and the vat define at least one upper opening situated above said passage, whereby liquid flowing into the first compartment is deflected upwardly through said upper opening into the second compartment.

4. An apparatus according to claim 2, wherein the partition wall and the vat define at least one lower opening situated below said passage, whereby liquid flowing into the first compartment is deflected downwardly through said lower opening into the second compartment.

5. An apparatus according to claim 2, wherein the partition wall and the vat define at least one upper opening situated above said passage, and at least one lower opening situated below said passage whereby a first part stream and a second part stream, respectively, of the liquid flowing into the first compartment is deflected upwardly through said upper opening and downwardly through said lower opening, respectively, into the second compartment.

6. An apparatus according to claim 3 or 5, wherein the deflecting means comprises a flow control means for controlling the liquid flow through said upper opening.

7. An apparatus according to claim 4 or 5, wherein the deflecting means comprises a flow control means for controlling the liquid flow through said lower opening.

8. An apparatus according to claim 2, wherein the first compartment has a horizontal cross-sectional area that decreases in the vertical direction from said passage.

9. An apparatus according to claim 8, wherein the horizontal cross-sectional area of the first compartment decreases from said passage to a level above the latter, and increases in the direction upwardly from said level.

10. An apparatus according to claim 3 or 5, wherein the upper opening is positioned such that the liquid flowing from the first compartment through the upper opening is directed downwardly into the second compartment.

11. An apparatus according to claim 1, futher comprising a horisontally extending hollow support beam for supporting the apparatus on the ground, the interior of the support beam communicating with said passage, whereby liquid to be filtered is supplied to the apparatus through said hollow suppport beam.