GB2153248A - Filter press plate assembly - Google Patents

Abstract

A filter press plate and inflatable diaphragm assembly (10) is disclosed for use in a filter press comprising a horizontal stack of such assemblies together or interleaved with recess plates (12). Each assembly (10) comprises a plate (11) and a diaphragm (19). Plate (11) has a thicker peripheral portion (13). Adjacent peripheral portion (13) the diaphragm does not overlie the plate (11) but has lips (23) accommodated in recesses (25) in the plate (10). This ensures that the clamping loads applied to the stack are not borne by the diaphragms. Filtrate passing through cloth (17) runs along channels (27) in the diaphragms to transverse channels (28), which communicate with corner eyes in aligned plates (11, 12). <IMAGE>

Description

SPECIFICATION Filter press This invention relates to a filter press.

Reference is made to co-pending application No. 8231844 from which the present application is divided.

A filter press is known which comprises a plurality of plates clamped in face to face relationship with intervening filter cloths and defining between each pair of plates a filter cavity in which a cake can be built up by pumping in a slurry via apertures in the plates, the stack consisting either entirely of filter plates, in which case each plate has between the or each operative surface thereof and an adjacent one of the filter cloths a flexible liquid-impermeable diaphragm which can be expanded away from the plate by fluid pressure to compress a cake in a filter cavity, or of alternate filter plates and plain recess plates, in which case each filter plate will have a diaphragm but each plain plate will have only a filter cloth associated therewith.Such a filter press allows a filter cake of high dry solids content to be formed in considerably less time than merely by continued pumping of the slurry into the press.

Difficulties have arisen, however, due to the construction of the plates and the diaphragms.

It is an object of the present invention to provide an improved filter press.

According to the invention there is provided a filter plate/diaphragm assembly for a filter press of the type described, wherein the filter plate has a peripheral thicker portion, the diaphragm having around its peripheral edge, a a lip which is disposed in the plate at is peripheral thicker portion.

The invention will be described further, by way of example, with reference to the accompanying drawings, wherein: Fig. 1 is a longitudinal cross-sectional view showing a half of a pair of plates in a filter press, one of the plates being part of a filter plate/diaphragm assembly of the invention, the cross-section being taken on line I-I of Fig.

4; Fig. 1 a is a fragmentary view showing a diaphragm before union of its ribs with its filter plate; Fig. 1 b shows a variation; Fig. 2 illustrates an additional feature of the invention; Fig. 3 is a transverse cross-section view (line i-l in Fig. 4) through a plate of the assembly of the invention; Fig. 4 is a front elevation of a plate/diaphragm of the invention; Fig. 5 is an enlarged detail of the diaphragm; Fig. 6 is a further enlarged detail of the diaphragm; Fig. 7 is a view similar to Fig. 6 but showing a variation; Fig. 8 is a fragmentary front elevation of the assembly shown in Fig. 2; and Fig. 9 is a similar view showing a variation.

A preferred filter plate/diaphragm assembly 10 of the invention is suitable for use in a filter press of the type described which has a plurality of assemblies 10, each having a filter plate 11, of uniform thickness, arranged in alternation with a plurality of plain recess plates 12 to form a horizontal stack, each filter plate 11 having a peripheral thicker portion 13, surrounding a smoothly curved and rounded hollow 14 defined by a thinner inner portion 15 surrounding a central through-aperture 16 and being substantially enclosed within a diaphragm 19.A filter cloth 17 encloses each assembly 10 and a filter cake can be built up by pumping a slurry via the central through passage to form a cake in each working chamber 18 defined by the hollows in adjacent plates, liquid passing through the filter cloths 17 and travelling along the working surfaces of the diaphragms 19 to drainage eyes 30 (Fig. 4) in, say, the corners of the plates 11 & 1 2 aligned to form a drainage passage extending lontitudinally of the stack.

Each plate 11, 12 is rounded at the central aperture and can have between the central aperture and the thicker outer portion a plural- ity of staybosses 20, 21 composed of a pair of protrusions 20a, 20b, 21a, 21b, extending from the respective plate 11, 12 one on each side thereof and contacting protrusions staybosses of adjacent plates in the stack to steady the plates, and maintain them separate. The protrusions 21 a of staybosses 21 of plates 12 are greater in size than those of plates 11 so as to extend outside the peripheries of staybosses 20 for apurpose to be later described.

Each plate 11 has its diaphragm 19 in the form of a first part 19a covering one side thereof and united at the centre with a diaphragm part 19b on the other side to form an envelope about the plate 11 to the inside of which a fluid such as compressed air can be introduced through ports 22 in the plate 11 to "inflate" the envelope and compress a partly-formed filter cake in the chamber between the plate 11 and plate 12 to increase its solids content by expulsion of liquor.Each diaphragm 19 does not overlie the peripheral thicker portion 13 of the plate 11 or the protrusions 20a, 20b of the staybosses 20, but has lips 23, 24 at its various edge portions, which lips 23, 24 are accommodated in complementary recesses 25, 26 in the inner periphery of the thicker edge portion and in the peripheries of the protrusions 20a, 20b this enabling the protrusions 20, 21 and the edge portions 13 of the plates 11 and thereof plates 13 to sandwich only the filter cloths 1 7 between them. thus reducing compressive stress on the diaphragms 19. Nevertheless.

the clamping together of the plates 11, 1 2 is effective to seal the diaphragms 19 to the plates 11 by urging the lips 23, 24 into engagement with the recesses 25, 26, these items being shaped to facilitate sealing.

The diaphragm 19 has a plurality of grooves 27 in its surface facing the cloth 17, which grooves 27 lead liquid passing through the filter cloth 17 to a drain channel 28 in one of two transverse ribs 2a in the diaphragm 19. Channels 28 can be restrained from closure by one or more solid inserts such as an open spiral or spaced tubular members (not shown). Ribs 29 are accommodated in complementary concavities in plate 11.

To encourage sealing between the diaphragm 19 and plate 11 at the lips 23, 24 and recesses 25, 26, the lips can be a force fit in the recesses as shown in Fig. Ia. Here lip 23 is shown being urged towards recess 23 by protrusion 21b during clamping. The lip 23 is wider than recess 26 and is thus compressed upon entry into the recess 26 to ensure a good seal. As a variation the lips 23 or 24 can each have a metallic or similar hard insert such as 29 which presents an outer edge 30 which, on insertion into the recess bites into the wall thereof and resists withdrawal of the diaphragm 19.

The transverse ribs 29 can terminate in extension 31 accommodated in the plate 11 and to prevent pressurised air from travelling between the extensions 31 and the plate 11 the extensions can be reinforced by having a tubular insert therein lining a through passage and aligning with passages 32 in the plate 11 or being accommodated therein. In the latter case the passages 32 can have shoulders to prevent movement of the inserts away from the diaphragms.

As an alternative to drainage grooves 27 (Fig. 6) the diaphragm 19 can have pips 33 which define drainage paths by supporting the cloth 17 clean of the diaphragm 19.

Fig. 2 shows a third feature of the invention, wherein a plate 35 similar in all respects to plate 11 has a diaphragm 36 which is in two complementary parts 37 one on each side of the plate 35.

At the centre of the plate 35, the edge portions of the central apertures in the diaphragms parts 37 are clamped together by an annular two part clamp 38 of outwardly facing C-section, the two halves 39 having rounded edges to reduce stress in the diaphragm parts 3, at this position and being united by setscrews, bolts or like fasteners 40. The edge portions of the diaphragms parts 37 at the centre may be reinforced by having flexible but inextensible members 41, 42 moulded in during manufacture. These members can take the form of an annular member 41 from which extend radial spokes 42, of metal or textile material Fig. 8. Alternatively Fig. 9 a metal plate 43 can be used having a central annulus 44 and radially outwardly extending fingers 45. The reinforcement tends to prevent ballooning of the diaphragm into the feed channel and bursting thereof when inflated.

The filter plate/diaphragm assembly of the invention has the advantage that if a diaphragm should become damaged it is only necessary to replace a small component and the whole plate does not have to be returned to the manufacture for repair.

The invention is.of course. applicable to filter presses having plates of different shapes and to presses wherein slurry feed is by an edge or at some position(s) other than a central position.

Other combinations of features are possible within the scope of the invention. For example, the invention can apply where each filter plate has one diaphragm on one side thereof and united with the central aperture in the plate (for example by an arrangement similar to that of Figs. 2. 8 and 9), the other side of the plate having a plain recess similar to that in plate 12 in Fig. 1. In a filter using such plate 1 diaphragm assemblies all the assemblies would be identical.

As a further variation the lower portions of lips 23, 24 can be inverted V-shape in crosssection to enhance sealing. To discourage bursting of the diaphragm adjacent the central feed aperture one or more annular inextensible reinforcing members can be moulded into the rubber or extensible plastics material of the diaphragm. Ligaments of limited extensibility can connect two such annulae or connect one such annulus to an annulus in a central clamp position if provided, to limit diaphragm movement away from the filter plate and into the feed aperture and adjacent space.

Claims (10)

1. A filter plate/diaphragm assembly for a filter press of the type described, wherein the filter plate has a peripheral thicker portion, the diaphragm having around its peripheral edge, a lip which is disposed in the plate at its peripheral thicker portion.

2. An assembly as claimed in claim 1 and clamped together with a plurality of similar assemblies in face-to-face relationship so that the peripheral thicker portions of adjacent assemblies make direct contact, the recesses and lips being so arranged that the clamping of the assemblies together securely locates the diaphragms and sealingly mounts them relative to the plates.

3. An assembly as claimed in claim 1 and clamped in a filter press together with a plurality of recess plates in alternate arrangement, the recess plates having wider peripheral portions so as to overlie the edges of the diaphragms and clamp them into sealing relationship with the diaphragm plates.

4. As assembly as claimed in claim 1, wherein the shape of the body of the diaphragm is such that it is relaxed in a position intermediate a first position where it closely overlies the adjacent surface of its associated filter plate and a second position, remote from the first position, which it attains when fluid, e.g. air, is pumped into the filter plate to cause the diaphragm to compress a filter cake in a filter chamber.

5. An assembly as claimed in claim 1, wherein the surface of the diaphragm remote from its filter plate, which surface faces a filter cloth, is provided with drainage pips and/or drainage grooves to allow the flow of filtrate from the outer surface of the filter cloth.

6. An assembly as claimed in claim 1, wherein the shape of the body of the diaphragm is such that when relaxed it fills or substantially fills the space adjacent the working surface of the associated filter plate, so that a filter cake will be built up by pressure of the slurry introduced, the cake as it is built up displacing the diaphragm towards the plate.

7. A filter plate/diaphragm assembly for a filter press of the type described wherein the diaphragm has over at least a portion of its periphery a rib which normally occupies a complementary recess in the plate, the rib being provided with a longitudinal drainage channel which communicates laterally with the working surface of the diaphragm and at one or both ends communicates with a drainage eye in the filter plate.

8. An assembly as claimed in claim 7, wherein communication between the longitudinal drainage channel in the rib and the drainage eye is by a passage in one end of the rib portion which communicates with a corresponding passage in the plate which leads to the drainage eye.

9. An assembly as claimed in any preceding claim, wherein the lip and recess have parallel sides, the width of each lip being greater than the width of its associated recess so as to be compressed upon engagement therewith.

10. An assembly as claimed in any preceding claim, wherein the lip has an insert presenting a sharp, hard edge disposed to discourage separation of the diaphragm from the plate.