WO2008053209A1

WO2008053209A1 - Improvements in and relating to solids separators

Info

Publication number: WO2008053209A1
Application number: PCT/GB2007/004152
Authority: WO
Inventors: Neville Earnest Lange; Richard Treve Mildren
Original assignee: Richard Mozley Limited
Priority date: 2006-10-31
Filing date: 2007-10-31
Publication date: 2008-05-08
Also published as: GB2443545A; GB0721432D0; GB0621614D0

Abstract

A centrifugal particulates solids separator comprises a rotatable separator drum (23) having one end wider than the other and means for rotating said drum about its axis, slurry introducing means whereby slurry can be poured onto the inside of the slurry drum to form a slurry film (20, 21) on the inside surface (22) of the drum and thereafter said film tending to migrate towards the wider end of the drum, and radially disposed scraper blade means (1) comprising a plurality of scraper blades (5) adapted to scrape the inside surface of said drum as it rotates and to preferentially cause denser particles (20) within the slurry to migrate towards the narrower end of the drum CHARACTERISED IN THAT said scraper blades (5) have a radial thickness relative to the axis of the drum which is less than the thickness of the film of slurry (20, 21), the arrangement being such that less dense solid particles (21) and / or the liquid forming part of the original slurry is able to flow over the scraper blades (5) and out of the drum (23) from its widest end and whereby denser solid particles (20) are preferentially scraped and separated out of the drum via its narrower end.

Description

Improvements in and relating to Solids Separators

BACKGROUND OF THE INVENTION

This invention relates to apparatus for separating solids from liquids, of the type discussed in GB2190609B (the disclosure of which is incorporated herein by reference), which describes a frusto-conical separator drum which is both rotatable and caused to vibrate about its longitudinal axis such that when particle-containing slurry material is introduced into it, usually along with wash water, high density "concentrate" particles are caused to preferentially exit from the narrower end of the drum and low density "tailings" particles are caused to preferentially exit from the wider, opposite, end of the drum. To aid separation and overcome the tendency of the denser particles to either remain stationery or begin moving to the wider end of the drum a series of vanes or blades are disposed peripherally around the inside of the drum so that the denser particles are effectively swept out of the narrower end of the drum whilst the lighter particles are washed over and around the blades to exit from the wider end of the drum as it rotates.

An improvement to the foregoing concept is disclosed in US 5037373 (also incorporated herein by reference) in which the vanes or blades are adapted to bear directly against the inside surface of the separator drum so as to overcome the problem otherwise of solid particles becoming trapped between the vanes or blades and the inside surface of the drum and as a consequence causing severe abrasion, leading to extremely short service life even when the vanes or blades are made from highly wear resistant material such as silicon carbide. Although the vanes or blades described in US5037373 act as effective scapers of particulates pinned to the inside of the separator drum by the centrifugal force imparted due to the rotation of the drum it will be apparent that they also act to inhibit the flow of the less dense particles within the slurry towards the wider, open, end of the drum and therefore may impair the efficiency of the separation process because of the indiscriminate way in which such scraper blades work. SUMMARY QF THE INVENTION

The present invention is derived from the realisation that it would be preferable for the scaper blades in such separators to be able to discriminate between dense and less dense particulates contained within the slurry and/or which are pinned to the inside of the drum by centrifugal force.

According to the invention there is provided a centrifugal particulates solids separator comprising or including a rotatable separator drum having one end wider than the other and means for rotating said drum about its axis, slurry introducing means whereby slurry can be poured onto the inside of the slurry drum to form a slurry film on the inside surface of the drum and thereafter said film tending to migrate towards the wider end of the drum, and radially disposed scraper blade means comprising a plurality of scraper blades adapted to scrape the inside surface of said drum as it rotates and to preferentially cause denser particles within the slurry to migrate towards the narrower end of the drum CHARACTERISED IN THAT said scraper blades have a radial thickness relative to the axis of the drum which is less than the thickness of the film of slurry, the arrangement being such that less dense solid particles and / or the liquid forming part of the original slurry is able to flow over the scraper blades and out of the drum from its widest end and whereby denser solid particles are preferentially scraped and separated out of the drum via its narrower end.

With this arrangement, it will be apparent that the densest particulates within the slurry, which are pinned against the inside surface of the drum by centrifugal force, are preferentially scraped by the blades such that the less dense particulates and the liquid itself, which may be primarily water, are collectively better able to exit from the separator drum without being substantially impeded by the presence of the scraper blades. As such the blades effectively substantially only scrape away the radially outermost layer of particulates, comprised of generally denser particulate solids, and gradually pushes them towards the narrower end of the separator drum.

The scraper blades are preferably slightly curved to correspond with the curvature of the inside of the separator drum when secured in their angularly offset operational position relative to the rotational axis of the drum and each may conveniently take the form of an elongated bar, such as a flat bar, from which extend one of more arms by which they can be secured to respective fixing plates, the fixing plates themselves being releasably securable to respective scraper blade mounting bars arranged radially around the periphery of the inside of the separator drum such that, when so mounted, the scraper blades can touch the inside surface of the drum during rotation of the scraper blade bars relative to the inside of the drum. In a refinement to this concept, the scraper blade fixing plates are partially pivotable about their mountings on the scraper blade bars with their respective scraper blades at positions sufficiently spaced therefrom so as to allow the scraper blades to move both radially due to centrifugal force during rotation on the scraper blade mounting bars without substantially altering the angle of attack of the blades relative to the inside of the separator drum end. Accordingly, the mass and physical size of the scraper blade fixing plates may be chosen to ensure close contact between the scraper blades and the inside of the drum during operation of the separator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a conventional scraper blade mounting bar showing both a conventional scraper blade and a scraper blade according to the invention;

Figure 2 is a partial side view on "A" of Figure 1 ; Figure 3 is a partial side view on "B" of Figure 1';

Figure 4 is a side view of a scraper blade according to the invention;

Figure 5 is a plan view of a scraper blade fixing plate for use with the scraper blade of Figure 4,

Figure 6 is a schematic side view of a conventional scraper blade in operation within a separator drum, and

Figure 7 is a schematic side view of a scraper blade according to the invention in operation within a separator drum.

DETAILED DESCRIPTION OF THE INVENTION

Referring firstly to Figure 1 , a conventional centrifugal solids-liquids separator scraper blade of the type shown in US 5037373 is shown generally at 1 mounted on a conventional scraper blade mounting arm or bar 2 (of which there are typically several in total arranged circumferentially within the drum) by means of a scraper blade fixing plate 3 and associated bolts (not shown). The scraper blade mounting bar 2 is positioned so that its major axis is generally parallel to the 'rotational axis "RA" of a slightly conical separator drum (not shown) although the line of the mounting bar 2 actually follows the cone angle. The scraper blade fixing bar 2 is adapted to rotate relative to the inside of the drum in the direction arrowed, thereby incrementally moving particulates solids trapped by the scraper blade 1 along the inside of the drum towards its narrowest end and against the tendency of the particulates solids to migrate towards its widest end. As will be appreciated, in doing so, the scraper blade 1 is indiscriminate in terms of the kind of particulates solids it will scrape towards the narrower end of the separator, although it will also be understood that in general, the denser

- particles will be moved more efficiently due to the fact that they are more effectively pinned to the inside of the rotating drum by centrifugal force. Nevertheless, the scraper blade 1 will still tend to move less dense particles in the wrong direction and in order to solve this problem and in accordance with the invention a low profile scraper blade 4 is used instead, seen more clearly with reference to Figures 3 and 4, where the scraper blade 4 has a relatively shallow and, preferably slightly curved blade portion 5 from which extends a pair of fixing arms 6 having flanged studs 7 at their free ends (seen more clearly with reference to Figure 4) which are received within correspondingly shaped sockets 8 set within a scraper blade fixing plate 9 (seen more clearly with reference to Figure 5) and welded thereto.

The scraper blade fixing plate 9 is secured underneath the scraper blade support bar 2 by a pair of bolts 10, 11 which extend through a pair of apertures 12, 13 in lugs 14, 15 extending from the scraper blade fixing plate 9, the aperture 12 being elongated to allow the plate 9 and hence scraper blade 4 to pivot within the range arrowed in Figures 2 and 3 towards the inside of the separator drum, the mass of the fixing plate aiding such pivoting movement as a result of the centrifugal force exerted upon it during rotation of the assembly within the drum, usually at slightly less or slightly more than the rotational speed of the drum itself. The bolts 10, 11 extend into corresponding guide bores/slots

16, 17 of a generally L-shaped anchor member 18 such that the scraper blade support bar 2 is sandwiched between the anchor member 18 and the scraper blade support plate 9. The scraper blade fixing plate 9 is designed to pivot in two planes, the first of which can be seen by reference to Figure 2, which allows the scraper blade 5 to follow the inside surface 22, including any imperfections, of the drum 23. The second pivot plane is shown with reference to Figures 1 and 3 where the bolt 11 acts essentially as a guide pin within the bore/slot 16 for the plate 9 which pivots by the amount indicated about the bolt 10 when secured within the guide bore 17. This ensures that the profiled, slightly curved, face of the scraper blade 5 has full contact with the surface of the drum 22 along its entire length. At the same time, the "attack" angle alpha "α" as shown in Figure 1 is maintained. As such, it will be noted that, in effect, the fixing plate 9 and associated blade 4 as shown in Figure 1 is effectively "towed" behind and about the bolt 10 and associated guide bolt 11 as shown in Figure 3.

In operation, upon rotation of the scraper blade support bar 2 within the slightly conical separator drum the centrifugal force exerted upon the scraper blade 4, improved by the mass of the scraper blade support plate 9, which is typically of stainless steel, ensures that the elongated blade element 5 maintains good contact with the inside surface of the separator drum and will typically tend to preferentially scrape away only the outermost regions of slurry consisting of the densist particulates solids, with the less dense solids and liquids freely flowing over the blade portion 5 and around the arms 6 outwardly towards the wider end of the separator drum. It will also be apparent that due to the spacing between the common line of the bolt receiving apertures 12, 13 and arm 6 receiving apertures 8 in the scraper blade fixing plate 9 that the tendency of the plate 9 to pivot due to centrifugal force imparted upon it during rotation will still ensure that the blade portion 5 of the scraper blade 4 remains firmly in contact with the inside of the separator drum, thereby ensuring that solid particulates are preferentially trapped by the blade portion 5.

Figures 6 and 7 show in operation, respectively, a conventional scraper blade within a separator drum (shown partially), and a scraper blade according to the invention, whereby particulates solids are being separated. In Figure 6 it will be seen that the blade portion 19 of the conventional scraper blade 1 is collecting concentrate 20 comprised of relatively dense particulate solids, as well as tailings 21 comprised of relatively less-dense particulate solids and liquid (if any), both of which are trapped behind the blade portion 19 above the inside surface 22 of the separator drum 23. In contrast, as will be seen from Figure 7, through the use of a low-profile blade portion 5 in accordance with the invention, the concentrate particulate solids 20 are preferentially scraped from the inside surface 22 of the separator drum 23 whilst the tailings 21 can freely pass over the blade portion 5, although it will be understood that in practice not all of the concentrate 20 is collected in one go and not all of the tailings pass freely past the blade portion 5 in one go, the operation instead being incremental in nature. Nevertheless, it will be understood that with the scraper blade 4 of the invention the less dense particulate solids that may otherwise be pulled off the front, narrower, end of the drum, are less prone to be, thereby increasing the concentration of the more dense particulate solids and, effectively, increasing the purity of the concentrate 20 by the time it reaches the narrower, exit, end of the separator drum 23. In addition, behind the slurry input point within the separator it will be apparent that more of the low density tailings 22 will be less prone to be fed towards the narrow end of the drum and hence be more likely to exit the wider end, thereby improving the overall efficiency of operation.

As a further refinement to the invention the scraper blade 4 may conveniently be provided with an elastomeric coating, such as a polyurethane coating, in order to increase wear resistance, more particularly at the working face of the scraper blade 5 and also to reduce friction due to trapped particles moving along the front face of the blade 5 as it rotates relative to the inside of the drum 22.

Claims

(1) A centrifugal particulates solids separator comprising or including a rotatable separator drum (23) having one end wider than the other and means for rotating said drum about its rotational axis (RA), slurry introducing means whereby slurry can be poured onto the inside (22) of the slurry drum to form a slurry film (20, 21) on the inside surface of the drum and thereafter said film tending to migrate towards the wider end of the drum, and radially disposed scraper blade means (1 ,4) comprising a plurality of scraper blades (5) adapted to scrape the inside surface of said drum as it rotates and to preferentially cause denser particles within the slurry to migrate towards the narrower end of the drum CHARACTERISED IN THAT said scraper blades (5) have a radial thickness relative to the axis (RA) of the drum which is less than the thickness of the film of slurry, the arrangement being such that less dense solid particles (21) and / or the liquid (21) forming part of the original slurry is able to flow over the scraper blades (5) and out of the drum from its widest end and whereby denser solid particles (20) are preferentially scraped and separated out of the drum via its narrower end. (2) A separator according to Claim 1 further characterised in that the radial thickness of the scraper blades is between the actual thickness of the concentrated denser solid particles and the remaining slurry tailings.

(3) A separator according to Claim 2 further characterised in that the radial thickness of the scraper blades is between the thickness of the scraped denser solid particulate concentrate and the less dense tailings as the combined slurry is being separated.

(4) A separator according to any preceding Claim further characterised in that the scraper blades (5) are curved to correspond with the curvature of the inside (22) of the separator drum (23) when secured in their operational position.

(5) A separator according to any preceding Claim further characterised in that the scraper blades (5) each take the form of an elongated flat bar from which extend one of more arms (6) by which they can be secured to respective fixing plates (9).

(6) A separator according to Claim 5 further characterised in that the fixing plates (9) are releasably securable to respective scraper blade mounting bars (2) and are arranged radially around the periphery of the inside (22) of the separator drum (23) such that, when so mounted, the scraper blades (5) can touch the inside surface (22) of the drum during rotation of the scraper blade bars relative to the inside of the drum.

(7) A separator according to Claim 6 further characterised in that the scraper blade fixing plates (9) are partially pivotable about their mountings (10, 11) on the scraper blade bars (2) and engage with their

- respective scraper blades (5) at positions sufficiently spaced therefrom so as to allow the scraper blades to move radially due to centrifugal force during rotation of the scraper blade mounting bars without substantially altering the angle of attack of the blades relative to the inside (22) of the separator drum (23).

(8) A separator according to any one of Claims 5 to 7 further characterised in that the mass and physical size of the scraper blade fixing plates (9) is chosen to ensure close contact between the scraper blades (5) and the inside (22) of the drum (23) during operation of the separator.

(9) A scraper blade means (4) comprising a scraper blade (5) adapted to scrape the inside surface of a centrifugal particulates solids separator drum characterised in that the scraper blade (5) is curved to correspond with the curvature of the inside (22) of the separator drum (23) when secured in its operational position. (10) A scraper blade (5) adapted to form part of scraper blade means according to any preceding Claim further characterised in being formed of an elongated flat bar from which extend one or more arms (6) by which it can be secured to a respective fixing plate (9).

(11) A fixing plate for releasably securing thereto a respective scraper blade (5) according to Claim 8, the scraper blade fixing plate (9) being partially pivotable when mounted on a scraper blade mounting bar (2) so as to allow, in use, the scraper blade (5) to move radially due to centrifugal force during rotation of the scraper blade mounting bar (2) relative to a separator drum (23).

(12) A method of separating particulates solids including the steps of: providing a centrifugal particulates solids separator comprising or including a rotatable separator drum (23) having one end wider than the other and means for rotating said drum about its rotational axis (RA), slurry introducing means, and radially disposed scraper blade means (1 ,4) comprising a plurality of scraper blades (5); rotating said drum about its rotational axis (RA); and using the slurry introducing means to pour slurry onto the inside

(22) of the slurry drum to form a slurry film (20,21) on the inside surface of the drum, thereafter said film tending to migrate towards the wider end of the drum; ' in which: the plurality of scraper blades (5) scrap the inside surface of said drum as it rotates to preferentially cause denser particles within the slurry to migrate towards the narrower end of the drum; and said scraper blades (5) have a radial thickness relative to the axis (RA) of said drum which is less than the thickness of the film of slurry, the arrangement being such that less dense solid particles (21) and/or the liquid (21) forming part of the original slurry is able to flow over the scraper blades (5) and out of the drum from its widest end whereby denser solid particles (20) are preferentially scraped and separated out of said drum via its narrower end.

(13) A centrifugal particulates solids separator including scraper blade means (4) substantially as hereinbefore described with reference to Figures 2 and 3 as further partially shown in Figure 1.

(14) A scraper blade (5) substantially as hereinbefore described with reference Figures 2, 3 as further partially shown in Figure 1.

(15) A fixing plate (9) for a scraper blade (5) substantially as hereinbefore described with reference to Figures 2 and 3 as further partially shown in Figure 1.