GB2204506A

GB2204506A - Separating screens

Info

Publication number: GB2204506A
Application number: GB08811291A
Authority: GB
Inventors: Charles Edward Allsop
Original assignee: SURESCREEN Manufacturing
Current assignee: SURESCREEN Manufacturing
Priority date: 1987-05-12
Filing date: 1988-05-12
Publication date: 1988-11-16
Anticipated expiration: 2008-05-12
Also published as: NZ224560A; DE3816214A1; GB2204506B; GB8811291D0; ZA883274B

Description

IMPROVEMENTS RELATING TO SEPAR2TING SCREENS is 2204s96 THIS INVENTION

relates to apparatus for the separation of solids from liquids and solids from solids by. screening. The invention is particularly concerned with improvements in or relating to separating apparatus of the type employing a rotary screen or trommel.

A typical separating apparatus oT this type comprises a hollow drum having an outer wall with a plurality of perforations formed therein. The material to be separated is fed into the drum while it is rotated so that a fresh screening surface is continually presented to the material, thus providing a relatively efficient separating process as comparedwith static screening.

The perforationzlin the drum wall will be of a size and shape depending on the type of material being processed. Thus, in its simplest form, the perforations may be relatively large sized apertures in a plane wall for the separation of large particles, as is described in U.S. Patent specification No. 2664204, or the perforations may be of a relatively small sophist.icated design such as those formed between parallel strands of 'wedge sectioned wire wound about support rods for the separation of liquids from solids, as is described in U.S. Patent Specification No. 3961605. Although this sophisticated design produces very good screening efficiency and substantially reduces any tendency of the screen to clog, even distribution of the sluiry or material to be separated is not always achieved, thur,

1 is 2. reducing the efficiency of the screen.

Other disadvantages of these known types of rotary separating apparatus are -unique to the specific type of material to be handled. For instance, in the separation of solids from raw sewage, or in the separation of sugar juice from the bagasse, the rotary drum must be of extended length to ensure adequate separation. This gives rise to substantial strain in the unsupported walls of the extended length drum which can cause the drum to break up in use. Furthermore, the use of internal deflectors to aid separation by increasing the residence time of the material within the drum, can also cause. structural problems which reduce the life of the drum.

It is therefore an object of the present invention to provide an improvement or modification of known type rotary separating apparatus which' obviates or at least minimises the aforementioned disadvantages.

According to one aspect of' the present invention, there is provided an apparatus for separating liquids from solids and/or solids from solids, which apparatus includes a trommel, the improvement wherein a tapered sleeve is fitted to the outlet end of the trommel, said tapered sleeve having a plurality of perforations formed therein.

The function of the tapered sleeve is to iucrease the duration of separation of the input materials by a greater amount in a given unit of length, than that which k 3.

will be provided in an equal length of the trommel. That is, the material to be separated is held back for a greater. length of time in the tapered sleeve than in an equivalent length of trommel to provide a substantially greater separation efficiency. Thus, in the case of liquid-solid separation, such as in. the case of sewage treatment, an increased felting effect results with up to 20% additional moisture removal. For solid-solid separation, such as in the case of grain cleaning, effectively 100% separatlon is achievable by the use of the tapered sleeve.

Preferably, the tapered sleeVe is formed' integrally with the trommel. In such an embodiment, it will generally be welded to the trommel. However, some situations may require the tapered sleeve to be a separable component such as when highly abrasive solids are being separated and wear and tear is likely to occur in the tapered sleeve, necessitating replacement. In this instance, the tapered sleeve is fitted to the trommal by releasable securing means. A preferred form of releasable securing means comprises a locking pin means such as a nut and bolt arrangement wherein the bolt extends through apertures in flanges formed on the adjacent edges of the trommel and the tapered sleeve.

The tapered sleeve has an inlet end which preferably has the same or approximately the same dimensions and shape as the outlet and of the trommel, and an outlet end which is of substantially reduced diameter compared with. the 4.

is inlet end. Since the shape of the tapered sleeve usually conforms with the shape of the trommel, it will usually have a frusto-conical shape as the trommel will generally be cylindrical. However, non regular trommals may in certain situations be preferred and may, for instance, be polygonal in cross-section. By polygonal is meant that the trommel has four or more substantially straight sides. A preferred polygonal cross- sectional shape, is a hexagon. The tapered sleeve will therefore also generally be of matching polygonal shape in cross-section.

It is, however also envisaged that the shape of the tapered sleeve may be quite different from that of the trommel. For instance, in certain situations a polygonal sectioned tapered sleeve may be used with a cylindrical trommel, or a frustum cone shaped sleeve may be used with a trommel of polygonal eross-section. Clearly in these situations the linkage between the trommal and the tapered sleeve will need to be adapted to accommodate the differences in shape. Thus, it may be that the outlet end of the trommel and/or the inlet end of the tapered sleeve are modified in shape to permit such linkage. Alternatively, a separate linking element could be used. Such an element may be in the form of a collar with one section matching the profile of the trommel and another section matching the profile of the tapered sleeve.

The perforations in the tapered sleeve preforibly 5.

is match the perforations in the trommel. Most preferably, the perforations are formed by wrapping support rods about a plurality of wedge profile screening wires arranged in a formation which produces the corresponding tapered construction.of the sleeve. Such wire and rods are preferably rgade from stainless steel but any material suitable for a particular type of separation may equally well be used. Such materials include a wide range of metal and plastics materials such as steel, copper, metallic alloys, polyurethane, polyvinylchloride, polybutylene, and the like.

Alternatively, the perforations in the tapered sleeve may be quite different from those in the trommel. They mayt for instance, be formed by punching holes in sheet material such as sheet stainless steel or plastics material, or they may be of a different size and configuration to those in the trommel. The tapered sleeve may also be manufacturedl from an entirely different material to that of the trommel.

A particularly---preferredform of tapered sleeve is formed by wrapping support rods on the bias over a plurality of wedge profile screening wires also arranged on the bias. This gives rise to a greater scalping effect in liquid-solid separation, and therefore greater separation efficiency. Most preferably, such a tapered sleeve Is matched with a trommel in which the wedge wire and support rods are wrapped in a similar biasing fashion. In the case of a cylindrical 6.

trommel, such biasing may produce a helically wound wire.

In use, the trommel is preferably supported for rotation at a small angle with respect to the horizontal to enable the intake feed of material to be separated, to flow under the combined action of gravity and the rotational velocity of the trommel. The tapered sleeve is fitted to the opening in the trommel which is supported lowermost and the degree of tapering in the sleeve is generally chosen so that a still smaller angle is made between the bottom section of the wall of the sleeve and the horizontal, as compared with that made by the wall of the trommel. This angle may vary essentially from zero up to about 100. This reduction in-inclination between the trommel and the bottom wall of the tapered sleeve results in the material to be separated, slowing down as it passes into the tapered sleeve thereby permitting further separation to occur. It has been found that by the addition of the tapered sleeve, a substantial increase in separation efficiency is achieved.. In the case of raw sewage treatment, approximately 75% of the moisture in the feed is removed in the trommel and by addition of the tapered sleeve, up to about 85% of the moisture is removed.

A satisfactory range of angles of taper for the tapered sleeve is from 40 to 150. More broadly the range may be from 1 to 200 e.g. 2 or 30 to170.

The tapered sleeve has a particular end use application in sugar juice recovery, sewage treatment, grain cleaning, paper pulp processing.

The invention also extends to the tapered sleeve per se.

1 1 1) is Preferred embodiments of the Invention will now be desczibed with reference to the accompanying drawings, in Which Fig. 1 is a side-on perspective of a separating apparatus incorporating a tapered sleeve according to the present invention; Fig. 2 is a side-on perspective of a frusto-conical shaped sleeve according to one aspect of the present Invention; and Pig. 3 is a side-on perspective of a hexagonal profile tapered sleeve according to another aspect of the present invention.

Referring to Fig. 1, there is illustrated an apparatus for separating liquids from solids or solids from solids, comprising a rotary screening drum or trommel 10 with a tapered sleeve 20 welded thereto. The trommel comprises a conventional cylindrical barrel 11 which is constructed of a plurality of longitudinally extending weage-shaped screening wires 12 and a plurality-of support rods 13 which are wrapped around the screening wires 12 to define a plurality of screening slots 17 therewith.

The trommel is supported adjacent each end by roller assemblies 14, 15 comprising pairs of trunion wheels on each side of the trommel (only one of each of which is illustrated). At least one of the roller assemblies is driven by conventional driving means (also not illustrated) L - is 8.

so as to cause rotation of the trommel and sleeve in use. The tapered sleeve 20 is welded to the outlet end of the trommel so as to extend beyond the support rollers 15 in a cantilever fashion.

The tapered sleeve 20 is formed in the same manner as the trommel 10 with a plurality of longitudinally extending wedge-shaped screening wires 21 and a plurality of transversely extending support rods 22 wound thereabout. The tapered sleeve has a generally frusto-conical configuration.

As illustrated, the trommel is inclined with respect to the horizontal so that the longitudinal cylindrical axis of the trommel makes an angle of approximately 51 with respect to the horizontal. The bottom wall section 16 of the tapered sleeve 20 is shaped to such a degree to provide an angle of approximately 1' "ith respect to the horizontal.

The separating apparatus will also include a reservoir for collecting the lIquid separated from a liquidsolid feed intake, or for collecting the fine grain material from a solid-solid particle feed intake. The reservoir will generally be in the form of a semi-cylindrical tray with upstanding sides which is located under the trommel and tapered sleeve, with the upstanding sides of the tray extending upwardly adjacent the walls of the trommel and tapered cleeve. The reservoir may adopt any number of configurations and has not been illustrated as it does not 1 is 9. form a part of the invention.

The feed inlet to the trommel (also not illustrated) may comprise a slotted pips extending pa2t-way along the intericir of the trommel, or an arrangement which projects the material to be separated, directly against the wall of the trommel adjacent the inlet end thereof. The input may be in the same direction of rotation of the trommel or against the rotation of the trommel, or in both directions as desired. Preferably, the direction of flow of the matizial at the point of inlet is substantially the same as the direction of rotation of the tzommel.

In operation, a slurry suspension or a solid-solid mixture of different sized particles, is feed into the trommel by known feed means In the direction shown by arrow A, while the trommel 10 and attached.sleeve 20 are rotated in either a clockwise or counter-clockwise direction. up;on entry into the trommel, the material to be separated Is continuously tumbled such that the liquid or fine grained component is passed outthrough the perforations 17 in the wall thereof as the material passes down the trommel. By the time the material reaches the tapered sleeve 20, most of it has been s%parated into its components, and the forward movement of the remaining material is suddenly reduced. The material is then subjected to a relatively longer holding time within the apparatus and this permits a greater degree of separation being achievable than would be possible in 1 I# - --I- is 10.

simply an extended length trommel. The solid component of a liquid-solid feed material, or the large sized fraction of a solid-solid particulate feed material, in extracted continuously from the outlet end of the tapered sleeve.

Referring now to Fig. 2, there is illustrated a further form of tapered sleeve according to the present invention. This comprises a frustoconical shaped sleeve having an inlet end 31 and an outlet end 32. The sleeve is formed by wrapping support rods 33 in a semi-helical fashion about a plurality of wedge-shaped screening wires 34 which are also arranged in a semi-helical fashion, defining apertures 38 therebetween. Flanges 35, 36 formed of metal rings are located at each end of the sleeve. Flange 36 is formed with apertures 37 to permit fixing to a trommel by bolts or the like.

The effect of the semi-helical wrapped wire is to further retard the axial flow of the material to be separated through the tapered sleeve, thereby permitting greater dewatering or fines staparation tha:a would otherwise be poscible.

Turning now to Fig. 3, a still further tapered sleeve embodiment is illustrated. The sleeve has a hexagonal profile with an inlet end 41 and an outlet end 42. It is f.;rmed by wrapping support rods 43 transversely about a plurality of wedge-shaped screening wires 44. Slots 45 ate formed between the overlapping wires 43, 44.

4 11.

1 Each end of the tapered sleeve has a flange 46,47. Flange 47 is circular in section and includes apertures 48 for attachment to a conventional cylindrical trommel by bolts or the like.

The hexagonal profile tapered sleeve has the advantage over the frustoconical shape in that it permits more vigorous movement of the material being separatedr and also prevents caking on the interior of the sleeve.

The axial length of the tapered sleeve shown in Figure 1 is about 60% of the axial length of the trommel. More broadly the sleeve may have an axial length in the range 30 to 100% e.g. 40 to 90% or 50 to 80% of the axial length of the trommel.

Whilst the above has been given by way of illustrative example of the invention, many modifications and variations may be made thereto by persons skilled in the art without departing from the broad scope and ambit of the invention as herein set forth in the following claims.

12.

Claims

An apparatus for separating liquids from solids and/or solids from solids which apparatus includes a trommel, the improvement wherein a tapered sleeve is fitted to the outlet end of the trommel, said tapered sleeve having a plurality of perforations formed therein.
2. An apparatus as claimed in Claim I wherein the tapered sleeve is integral with the trommel.
3. An apparatus as claimed in Claim I wherein the tapered sleeve is fitted to the trommel by releasable securing means.
4. An apparatus as claimed in Claim 3 wherein the releasable securing means comprises a locking pin.
5. An apparatus as claimed in any one of the preceding claims wherein the trommel is cylindrical in shape and the tapered sleeve has a frustum shape.
6. An apparatus as claimed in any one of Claims 1-4 wherein the trommel has a polygonal cross-section and the tapered sleeve has a corresponding polygonal cross-section.
7. An apparatus as claimed in any one of the preceding Claims wherein the perforations in the tapered sleeve match the perforations in the trommel wall.
8. An apparatus ae claimed in any one of the preceding claims wherein the perforations in the tapererl sleeve are formed by wrapping support rods about a plurality Of Wedge shaped screening wires arraiged in a correspondingly tapered z 13 orientation.
9. A tapered sleeve for use in apparatus for separating liquids from solids and/or solids from solids incorporating a trommel, said tapered sleeve having a plurality of perforations formed therein.
10. A tapered sleeve as claimed in Claim 9 which has a frustum shape.
11. A tapered sleeve as claimed in Claim 9 which has a frustal polygonal e.g. pyramidal or hexagonal shape.
12. A tapered sleeve as claimed in any one of Claims 9-11 wherein the perforations are formed by wrapping support rods about a plurality of wedge-shaped screening wires arranged in a formation to produce the corresponding tapered construction of the sleeve.
13. An apparatus for separating liquids from solids and/or solid is from solids substantially as hereinbefore described with reference to the accompanying drawings.
14. A tapered sleeve for use in apparatus for separating liquids from solids and/or solids from solids incorporating a trommel, substantially as hereinbefore described with reference to the accompanying drawings.

Published 1986 at The Patent Office, State House, 66.171 High Holborn, London W01R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Maxy Cray, Kent. Con. 1187.