IE51325B1 - Apparatus for segregating pulverised material - Google Patents

Description

APPARATUS FOR SEGREGATING PULVERISED MATERIAL This invention relates to apparatus for separating pulverised material on a particle size basis.

In a known form of refuse treatment apparatus the refuse is fed into one end of a horizontally disposed rotary treatment drum which subjects the refuse to a break-down or fragmentation process, the axial length of the drum being sufficiently long that the residence time of the refuse in the drum is such that on emergence from the other end of the drum it is in a fragmented form of limited particle size and organic constituents of the refuse are uniformly dispersed. Usually the treated refuse as discharged from the rotary drum is of relatively high moisture content and is subjected to further processing by rotary screens in order to separate the treated refuse in order of particle size. Thus fines having an average particle size up to the order of 50 mm are separated from larger particles. These fines are valuable as a supplementary fuel or for production of compost or as a surface covering for land fill sites since the refuse treatment process does not destroy the bacteria in the refuse and the fines tend to break down further, after disposal or storing, by bacterial action.

In the known apparatus the drum diameter is of the order of 10 or 13 feet (3-4 meters) and the axial length is considerably greater than the diameter, for example 40-70 feet (12-20 meters).

The rotary screens which effect segregation of the treated refuse on a particle size basis are in the form of an extension to the rotary drum being of substantially the same diameter as the drum, screened material being collected by a chute arrangement which directs the collected material on to a belt conveyor, the screened material moving through the chute under the influence of gravity. Because the screened material has a relatively high moisture content it tends to adhere to the side walls of the chute resulting in blockage of the passageway through the chute. To overcome this problem the chute side walls are arranged with substantial angles of inclination and this has resulted in a compromise between axial length of the screens, width of the conveyor and distance of the conveyor beneath the screens. Furthermore, since the rotary drums and screens are located as near ground level as is possible to facilitate maintenance and to minimise cost of erection, thr chute and conveyor are usually located in a pit beneath the screens. Thus if the rotary screens are axially lengthened to increase separation efficiency whilst the chute side walls are maintained at the same angle of inclination the depth of the pit required becomes very considerable .md this is expensive to construct and additionally results in an increased length of conveyor since the discharge point from the conveyor is usually at a predetermined height, such as for example is required to load a transport vehicle.

It is an object of the present invention to provide an improved form of apparatus for segregating pulverised material which obviates or mitigates the foregoing disadvantages.

According to the present invention there is provided apparatus for segregating pulverised material on a particle size basis, comprising a rotary drum having a substantially horizontal axis of rotation at one axial end of which there is releasably mounted thereon a segregation assembly comprising inner and outer concentric screen walls, each wall being perforated, the inner screen wall having substantially larger perforations than the outer screen wall, and the end face of the assembly remote from the drum being open, a non-rotatable housing encasing the lower part of the said assembly and co-operating with helical rib members secured to the outer surface 1θ of the outer screen wall to deliver material passing through the perforations of the outer screen wall to a first collection station located at a predetermined axial position along the segregation assembly, first conveyor means co-operating with said first collection station to effect removal of material delivered thereto, said housing further defining a second collection station at said open end of said segregation assembly for receiving material axially discharged therefrom, second conveyor means co-operating with said second collection station to effect removal of material delivered thereto.

The screening surface of the outer rotary screen wall may be provided with guide means forming a continuous channel for movement of material under treatment so as to prolong the treatment period.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figures IA and IB show front and side view of known refuse treatment apparatus; Figures 2A and 2B illustrate an embodiment of the present invention in front and end views; and Figure 3 illustrates a modification of the Figure 2 embodiment.

The refuse treatment apparatus shown in Figure 1 incorporates a 30 horizontally disposed rotary drum 10 mounted on external bearings (not shown; and supporting at its free end a releasably mounted drum assembly 11 which comprises inner and outer concentric screen walls 12, 13 each being perforated, tne inner wall 12 having relatively large perforations of the order of 150 mm diameter (6 inches) and the outer wall 13 having perforations of the order of 50 mm diameter (2 inches). Walls 12 and 13 are united to form a unit which is attachable to the drum 10 so as to be rotatable therewith about a rotational axis 9. At the end 1OA of the drum 10 adjacent the assembly 11 there is an end plate incorporating an aperture adjacent the periphery of the drum 10 through which pulverised refuse is delivered to the interior of the drum assembly 11. A sliding door is fitted over this aperture in order to vary the effective aperture size so that the quantity of material delivered to the drum assembly 11 can be varied as required.

Partially surrounding the outer wall 13 is a fixed hopper device 14 arranged to collect screened material passing through wall 13, the lower portion of the hopper device 14 forming a chute 15 the side walls of which are inclined relatively steeply for the reasons previously discussed and the chute delivers collected material on to a conveyor 16 for elevation to a discharge point above ground level. The lower end of the chute 15 and the lower end of the conveyor 16 are located in a pit 17 beneath ground level.

In operation of this known apparatus pulverised refuse is delivered from drum 10 to the interior of the assembly 11 for screening thereby. Particles smaller than about 150 mm diameter pass through wall 12 for further screening by wall 13 and particles of size less than about 50 mm diameter pass through screen 13 for collection by hopper 14 and delivery on to conveyor 16. Material which fails to pass through wall 13 is driven by the rotary movement of assembly 11 to be discharged from the open end ΠΑ of assembly 11 remote from drum 10, being collected by a further conveyor 18.

Conveyor 18 also collects material which fails to pass through wall 12. Conveyor 18 is also located in pit 17 and elevates the discharged material to a discharge point above ground level.

The arrangement shown in Figure 2 is in accordance with the present invention from which it will be evident that the lower half of the screen walls 12 and 13 are surrounded by a non-rotatable housing 26 which has an aperture 27 arranged for delivering material having passed through screen wall 13 to a conveyor 16. Aperture 27 is aligned with a gap formed between rib members 29 secured to the outer surface of outer screen wall 13 and arranged in a general helical configuration to drive material passing through wall 13 and collected by housing 26 towards the aperture 27. It will be evident that the lov/er end of conveyor 16 is much closer to the rotary axis of the assembly 11 than is the case in the Figure 1 arrangement and furthermore the pit 17 within which conveyor 16 is located is much shallower. As with the arrangement in Figure 1 a second conveyor 18 is provided to collect material, axial discharge from the open end of the assembly 11 being constrained by a hopper device 14 which in this arrangement is simply in the form of a plate and access to the conveyor 18 through the housing 26 being by way of a second aperture 28 therein.

In the context of pulverised refuse treatment the fines discharged through screen 13 incorporate relatively heavy particles such as bottle tops, glass fragments, stones, nails, etc. which cause a cleaning action to occur on the internal surfaces of housing 26 and contribute towards the natural axial flow of collected material towards aperture 27. The presence of such heavy particles prevents the annular chamber between housing 26 and screen wall 13 becoming blocked with moist fines.

In the Figure 3 arrangement the inner screen wall 12 is arranged as previously but the outer screen wall 13 is provided on its inner surface with upstanding ribs 30 which form a continuous passageway over the surface of the wall 13 and extending axially from the drum 10 (see Figure 3). In this arrangement material passing through screen wall 12 is constrained by the rib formation 29 to follow a predetermined path so that the residence time of the material on the screen wall 13 is increased. The outer housing although not shown is as illustrated in Figure 2.

Claims (3)

1. Apparatus for segregating pulverised material on a particle size basis, comprising a rotary drum having a substantially horizontal axis of rotation at 5 one axial end of which there is releasably mounted thereon a segregation assembly comprising inner and outer concentric screen walls, each wall being perforated, the inner screen wall having substantially larger perforations than the outer screen wall, and the end face of the assembly remote from the drum being open, 10 a non-rotatable housing encasing the lower part of said assembly and co-operating with helical rib members secured to the outer surface of the outer screen wall to deliver material passing through the perforations of the outer screen wall to a first collection station located at a predetermined axial position along the segregation assembly, 15 first conveyor means co-operating with said first collection station to effect removal of material delivered thereto, said housing further defining a second collection station at said open end of said segregation assembly for receiving material axially discharged therefrom, second conveyor means co-operating with said second 20 collection station to effect removal of material delivered thereto.

2. Apparatus as claimed in claim 1, wherein the inner surface of the outer screen wall is provided with an upstanding rib formation forming a continuous passageway extending over substantially the entire area of said inner surface for constraining movement and prolonging residence 25 time of material under treatment.

3. Apparatus for segregating pulverised material on a particle size basis, substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings. tAns & CO.,