GB2025268A

GB2025268A - Method and Apparatus for Separating Materials

Info

Publication number: GB2025268A
Application number: GB7924629A
Authority: GB
Original assignee: TAYLOR HITEC Ltd
Current assignee: TAYLOR HITEC Ltd
Priority date: 1978-07-15
Filing date: 1979-07-16
Publication date: 1980-01-23

Abstract

Individual constituents are separated from an aggregation of materials by passing the same along a chute 30 having branches 36 into which the constituents are selectively deflected by the application of magnetic fields at the junctions between the chute 30 and its branches, by the induction of eddy currents in conductive constituents, the interaction of such eddy currents with a magnetic field generated by a coil 46 causing deflection. <IMAGE>

Description

SPECIFICATION Method and Apparatus for Separating Materials This invention concerns the separation of individual constituents from an aggregation of materials, for example, the separation of metals from non-metals or of different metals from one another.

This invention is particularly suited to the breakdown of scrap for recycling and disposal as appropriate, and more especially to the sorting of waste from nuclear power stations, wherein safety is a significant factor to be taken into account, in order to facilitate processing prior to storage or disposal. However, the invention is not intended to be confined to such applications.

In nuclear power stations, much of the waste is contaminated and cannot safely be processed without taking elaborate precautions to protect any personnel involved in the processing from radiation. Ideally, therefore, sorting of the waste should be carried out by apparatus which not only operates automatically but which in addition is capable of satisfying rigorous conditions of reliability and is designed for ease of maintenance.

It is an aim of this invention to provide such apparatus, and another aim is to provide a method for automatically separating materials without the need for using apparatus with moving parts to achieve the separation.

According to one aspect of the invention, a separator comprises a main chute having an inlet for receiving an aggregation of materials, at least one auxiliary chute branching from the main chute, and means for producing at the junction of the main chute and said at least one auxiliary chute a magnetic field arranged so as to induce in a conductive body moving along the main chute in the region of the junction eddy currents tending by reaction with the field to deflect the body into the auxiliary chute.

An advantage of such apparatus lies in the lack of any need for moving parts in that the chutes may be fixed in the desired location whilst the means for producing a magnetic field may comprise an electromagnet secured adjacent to the chutes with each coil turn being elongate and extending generally in the direction of said at least one auxiliary chute and across the main chute.

Without moving parts, a cause of wear is avoided and this promotes reliability, in the sense of durability, of the apparatus.

In use, the main chute is arranged so that the aggregation of materials falls therein under the action of gravity. Whilst it is feasible for the main chute to be inclined relative to the vertical, in one form of the invention the main chute is intended to extend vertically whilst said at least one auxiliary chute extends downwardly from its junction with the main chute making an acute angle of, for example, 450 with the main chute.

Separation of materials within the apparatus is achieved in that the force exerted on an individual body within the main chute is a function of the magnitude of the induced eddy currents, this in turn being a function of the resistivity of the material comprising the body, the body's dimensions and the magnetic field strength; the force required to deflect the body into the auxiliary chute is a function of the dimensions of the main chute, the distance the body has fallen and the mass of the body; and thus by selecting the magnetic field strength, the dimensions of the main chute and the location of the junction appropriately it is possible to a reasonably accurate extent to control the separation of a particular metal from the remaining materials assuming that the masses and dimensions of bodies of that metal do not vary too widely.The remaining materials may be other metals, for example of higher resistivity than that already separated, and/or non-conductive materials.

Additional auxiliary chutes may be provided to separate further metals if desired.

Another aspect of the invention features a method of separating materials comprising dropping an aggregation of the materials, and applying a magnetic field to the aggregation so as to induce in those materials which are conductive eddy currents tending by reaction with the field to deflect the conductive materials sideways.

The invention is described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a flow diagram of a system incorporating a separator embodying the invention; Fig. 2 is a perspective view of a portion of the separator; Fig. 3 is a plan view of the separator and other elements of the system; and Figs. 4 and 5 are diagrammatic face and side views respectively of an electromagnet of the separator illustrating the operation of the separator.

The system shown in Fig. 1 is designed for sorting waste from nuclear power stations into its constituent materials for subsequent storage or disposal. The waste in question is a mixture of magnox, stainless steel, zircaioy and graphite elements, struts of the graphite being joined to members made of the stainless steel and the zircaloy. Before separation of the constituents of the waste can take place any physical bonds between the different elements must be broken and this is achieved by passing the waste through a crusher 1 0. In the crusher 10, the graphite is broken into small particles thus being detached from the stainless steel and zircaloy, and the metal elements are at least partially flattened and compacted.

After leaving the crusher 10 the comminuted waste is dropped through a separator generally designated 1 2. The separator 12, which is described in further detail hereinafter, initially divides the magnox from the remaining waste and directs this to a compactor 14 from which the magnox is passed to a store or a disposal unit 1 6.

Similarly, the stainless steel and zircaloy are divided from the crushed graphite and are directed to a compactor 1 8 and thence to a store or a disposal unit 20. Finally, the crushed graphite drops from the separator 12 and is conveyed into a store or a disposal unit 22.

Referring now to Fig. 2, which shows a portion of the separator 12 in detail, the separator 12 comprises a main chute 30 arranged to extend vertically below the crusher 10. The chute 30 is in the form of an enclosed duct having an inlet 32 in communication with an outlet (not shown) of the crusher 10 and an outlet 34 in communication with an inlet (not shown) of the store or disposal unit 22. Branching from the main chute 30 are two auxiliary chutes 36, only one of which is illustrated in Fig. 2. The number of auxiliary chutes 36 provided is dependent upon the number of materials to be separated and may thus be one or more. However, only one need be mentioned in any detail since the arrangement of the others, if there is more than one, is similar.

Like the main chute 30, the illustrated auxiliary chute 36 comprises an enclosed duct. The auxiliary chute 36 is mounted on the main chute 30 so as to extend downwardly from an inlet 37 of the chute 36 at an acute angle, which in the present instance is 450, with the axis of the chute 30.

Both the chute 30 and the chute 36 have flat front walls 38, 40 respectively which merge into one another, and likewise flat rear walls 42, 44 arranged parallel to the walls 38, 40. Mounted on the walls 38, 40 externally of the two chutes is a first electromagnet 46, a second electrogmagnet 48 being disposed opposite the first on the walls 42, 44. The coil of each electromagnet 46, 48 is arranged so that the turns 50 are each elongate and largely extend parallel to, in overlapping relationship with, the chute 36, projecting beyond the inlet 37 of the chute 36 across the chute 30.

Whiist it is not essential for the electromagnets to overlap the inlel end of the chute 36 as well as spanning the chute 30 as shown in Fig. 2, this is preferred since it enhances the performance of the separator.

As can be seen in Fig. 3, the separator 12 and compactors 14, 18 are all housed within a concrete shield 70 to protect personnel from radiation. The shield 70 has a plug 72 permitting access to such apparatus for maintenance or repair. An electric control arrangement 74 located outside the shield is connected to the two electromagnets 46, 48 for varying the current passed through the turns 50 and thus for varying the magnetic field strength of the electromagnets.

A drive 76 for the compactors 14, 18 is also situated outside the shield 70.

Operation of the separator 12 is as follows:- When a current is passed through the turns 50 of the electromagnet 48 as indicated by the arrows I in Fig. 4, a magnetic field represented by the flux lines X in Fig. 5, which is a view taken in the direction of the arrow A in Fig. 4, is created.

Now when an electrically conductive body 80, such as an element of Magnox, falls down the chute 30 under the action of gravity in the direction of the arrow B in Fig. 4 eddy currents are induced in the body as it passes adjacent to the electromagnet 48. These eddy currents are represented by dashed loops L in Fig. 4 and react with the magnetic field to produce a force R perpendicular to the elongate portions of the turns 50. Because these portions are inclined relative to the vertical so also is the force R and thus the force R may be resolved into a vertical force -f causing deceleration of the body and a horizontal force D deflecting the body sideways.

By appropriate selection of the force D, the body 80 is deflected sideways sufficiently to propel it into the auxiliary chute 36. The magnitude of the force D required to deflect a given body into the auxiliary chute is dependent upon the mass of the body, the distance it has fallen and the dimensions of the main chute 30.

At the same time the deflection force actually exerted on a given body is dependent upon the magnitude of the eddy currents induced in that body. The eddy currents themselves are affected by the resistivity of the material of the body, generally being of greater magnitude for materials of lower resistivity than for materials of higher resistivity, by the dimensions of the body and by the magnetic field strength. Thus by arranging the electromagnets to provide a given field strength, bodies of a particular material and similar dimensions may be separated from the remaining waste as desired.

It will be appreciated that when various different materials are to be separated in turn, the order of separation will be determined according to the relative forces exerted on each in a given field so that materials of lowest resistivity, which are thus generally subject to the highest deflection forces, may in general be deflected into a respective auxiliary chute first, although where complex calculations are required to determine the deflection forces exerted, for example, by virtue of the complex structure of a particular body it may be preferable to determine the order of separation empirically.

Amongst the modifications possible to the described apparatus are the provision of an electromagnet or electromagnets which span the chute 30 but do not overlap the chute 36, although this provides less control during deflection of conductive bodies, and the replacement of a vertical main chute with one which is inclined to the vertical. Another possibility is to replace one of each pair of electromagnets with a pole piece made of mild steel. In this case, faces of the electromagnet and the pole piece may constitute wall portions of the main chute.

Claims

1. A method of separating individual constituents from an aggregation of materials, comprising the steps of arranging for said aggregation of materials to fall under gravity along a path having a vertical component sufficient to produce movement of said aggregation in said path, and applying to said aggregation a magnetic field which induces in those materials which are electrically conductive, eddy currents tending to react with said field to produce forces by which said conductive materials are deflected laterally out of said path.

2. Separator apparatus for separating individual constituentsfrom an aggregation of materials, comprising a main chute having an inlet for receiving said aggregation of materials and defining for said materials a path having a vertical component sufficient to produce movement under gravity of said materials along said path, at least one auxiliary chute branching from the main chute, and means for producing at the junction of the main chute and said auxiliary chute, a magnetic field arranged to induce in an electrically conductive body moving along the main chute in the region of the junction, eddy currents tending to react with said field to produce a force by which said body is deflected into the auxiliary chute.

3. Separator apparatus as claimed in claim 2, in which the main chute is vertical and said auxiliary chute extends downwards at an acute angle from its junction with the main chute.

4. Separator apparatus as claimed in claim 2 or claim 3, in which the means for producing a magnetic field comprise an electromagnet located adjacent to the junction of the chutes and having an energising coil of which the turns are elongate, and extend across the main chute generally in the direction of said auxiliary chute.

5. Separator apparatus as claimed in claim 4, comprising a further electromagnet located adjacent said junction on the opposite side thereof to the first-mentioned magnet.

6. Separator apparatus as claimed in claim 4 or claim 5, in which the or each electromagnet overlaps the inlet end of the auxiliary chute.

7. Separator apparatus as claimed in any one of claims 2 to 6, further comprising compactor means at the end region of each chute for receiving and compacting material fed thereo from said chute.

8. Separator apparatus as claimed in claim 7, further comprising a nuclear radiation shield housing said chute, electromagnet means and compactors, and control means and/or drive means for said electromagnet means and said compactors arranged externally of said radiation shield.

9. A method of separating individual constituents from an aggregation of materials, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. Separator apparatus for separating individual constituents from an aggregation of materials, constructed, arranged and adapted to operate substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.