GB2102297A

GB2102297A - Tube pressure filter

Info

Publication number: GB2102297A
Application number: GB08122319A
Authority: GB
Inventors: John Lawrence Martin
Original assignee: Alfa Laval Ltd Great Britain
Current assignee: Alfa Laval Ltd Great Britain
Priority date: 1981-07-20
Filing date: 1981-07-20
Publication date: 1983-02-02
Also published as: DE3226915A1; JPS5834015A; GB2102297B

Abstract

The slurry inlet (22) of a tube pressure filter is formed in the inner tubular assembly (17, 18, 19) of the filter, and after introduction of slurry the inner assembly is moved upwards a short distance (Fig. 3 not shown) to an operative position in which contact of the inflatable membrane (5) against the inlet (22) is prevented by positioning of the inlet (22) within an annular shield formed by upper end ring (7) of the outer assembly, thus obviating damage to the membrane by its being pressed against the edges of the inlet (22). After the filtering and pressing, the inner assembly is moved down out of the outer assembly to discharge the cake. <IMAGE>

Description

SPECIFICATION Tube pressure filters The invention relates to tube pressure filters, of the type known for example, from British Patent Specification 907485, comprising a pair of coaxial generally tubular assemblies arranged one with the other and an elastically extensible tubular membrane arranged between the assemblies to define an inner slurry compartment bounded by the inner assembly and the membrane, and an outer pressure compartment bounded by the membrane and the outer assembly. In use, slurries are fed to the inner compartment and fluid pressure is applied to the outer compartment to cause the membrane to express liquid from the inner compartment through the inner assembly, the main part of which is constructed as an annular filter.

The membrane in such a press is secured to the outer assembly, and the inner assembly is axially displaceable relative to the outer assembly to facilitate removal of the filter cake which forms on it and for occasional maintenance of the inner assembly.

Normally, slurry to be filtered is fed to the inner compartment through a slurry inlet formed in the inner tubular assembly in the form of a narrow annular slot, which may or may not be subdivided into arcuate segments by spaced partitions.

Slurry is forced into the inner compartment whilst the press is closed prior to the application of pressure to the outer compartment to effect filtering or dewatering. In the pressure filtering state the membrane is pressed against the slurry and also against the slurry inlet, and this results in a tendency for the membrane to be damaged by partial extrusion or cutting of the membrane against the edges of the slurry inlet.

Attempts have been made to overcome this problem by engaging an elastic seal about the slurry inlet to act as a one-way valve for the admission of slurry, whilst protecting the membrane from being pressed against the orifice edges during pressure filtering, but the elastic seal itself is prone both to damage and to being unseated by large particles lodging under it.

The present invention aims at reducing or obviating these problems and resides broadly in the provision of a tube pressure filter in which the inner tube assembly is axially movable relative to the outer tube assembly from a first feed position in which the slurry inlet communicates freely with the inner compartment, to a second, operative position in which the slurry inlet is positioned within an annular shield which prevents its being contacted by the membrane.

One form of tube pressure filter in accordance with the invention is described below, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a vertical cross-section of the filter; and Figures 2 and 3 are details of the filter, on a larger scale, showing two different operative positions.

The tube pressure filter shown in Figure 1 comprises an outer tubular assembly 1 secured to a support frame, and an inner tubular assembly 3 secured to a jack 4 by which its axial position, relative to the assembly 1 is adjustable.

The annular space between the two assemblies contains an impermeable elastic membrane 5 secured by annular beads at each end to the outer assembly, the main components of which are a main tubular body 6, annular top and bottom end flanges 7, 8 and annular top and bottom hydraulic feed rings 9. The membrane is shown in close contact with the interior of the body 6, where it is held by partial vacuum, during the feeding of slurry into the space 11 formed between the membrane and the inner tubular assembly 3.

The assembly 3 comprises a main perforated tubular body 13 to the lower end of which are secured a bottom closure plate 14, bottom fairing ring 15 and bottom fairing 16.

At its upper end, the body 13 has secured to it a top fairing ring 17, a slurry feed ring 18 and top fairing 19. These components define an annular gallery for the supply of feed slurry from a main inlet (or inlets) 21 to an annular slurry feed orifice 22, as will be seen more clearly in Figures 2 and 3.

In Figure 2, the parts are in position for feeding slurry to the inner compartment 11 of the filter with which the slurry feed orifice 22 is in direct communication.

The top fairing ring 17 is dimensioned to make a close sliding fit in the bore of the end of flange 7, to which it is sealed by an O-ring seal 24 housed in an external groove in the ring 17.

When slurry feeding has been completed by fully charging the inner compartment, the jack 4 is operated to raise the inner tubular assembly to the position shown in Figure 3, in which the orifice 22 is positioned within the bore of the end flange 7, which thus constitutes an annular shield preventing contact of the membrane 5 with the edges of the orifice 22 during pressure filtering. In this phase of operation, the membrane is pressed against the fairing ring and lower portion of the tube ring, without any danger of the membrane being forced into the feed orifice and by the same token seals off the orifice from the inner compartment.

A further advantage of the specific construction illustrated is that the seal 24 moves along a smooth, uninterrupted bore, and is thus protected from damage by "nibbling" due to passing over apertures or other edges. It will be noted that the lower, inner margin of the top flanges 7 is radiused at 7A to ease passage of the seal across this region during opening and closing of the press.

In the illustrated embodiment, the relative displacement of the inner tubular assembly between the feed position of Figure 2 and the operative position of Figure 3 is of the order of 12 mm.

Opening of the press after dewatering to facilitate removal of filter cake is conventional, the inner tubular assembly being displaced downwardly some 300 mm.

It will be appreciated by those skilled in the art that the above described features are readily applicable and adapted to a bottom feed arrangement, although a top feed arrangement, as illustrated is generally to be preferred.

Claims

1. A tube pressure filter comprising a pair of coaxial generally tubular assemblies arranged one within the other and on elastically extensible tubular membrane arranged between the assemblies to define an inner, slurry compartment between itself and the inner assembly, and an outer, pressure compartment between itself and the outer assembly, the membrane being secured at its ends to the outer assembly and the inner assembly being formed near one end with a slurry inlet, and in which the inner tubular assembly is movable axially, relative to the outer assembly, between a feed position, in which the slurry inlet communicates freely with the inner compartment and a second, operative position in which the slurry inlet is positioned within an annular shield which prevents its being contacted by the membrane.

2. A filter according to claim 1, wherein the said shield is constituted by an annular member forming part of and fast with the outer assembly, the said inlet being positioned within the annular inner surface of the said member in the operative position.

3. A filter according to claim 2, wherein the slurry inlet is formed as an annular slot positioned axially inwardly of an end member of the inner assembly, the said end member having sealed, sliding engagement in the said annular member of the outer assembly.

4. A tube pressure filter substantially as herein described with reference to the accompanying drawings.