EP0659487A1

EP0659487A1 - Mobile dense-medium separating apparatus

Info

Publication number: EP0659487A1
Application number: EP94309694A
Authority: EP
Inventors: Adrian Parnaby
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-12-22
Filing date: 1994-12-21
Publication date: 1995-06-28
Also published as: GB2285000A; GB9326144D0

Abstract

A mobile dense-medium separating apparatus comprises a rotatable drum (12), arranged with its axis generally horizontal and having at one end an aperture (16) through which solids and liquid may be introduced into the drum and at the other end an aperture (17) through which solids and liquid may exit the drum, means (10, 11, 21) to convey solids and liquid to and away from said drum, means (18) to rotate said drum about its longitudinal axis and means (30, 31) to enable the apparatus to be readily moved between locations.

Description

The present invention relates to apparatus for dense-medium separation such as is used for separating a dense solid from a less dense solid.
Dense-medium separation is used, for example, in the coal industry for separating high quality coal from relatively dense impurities or coal of lower quality. Separation is carried out by washing the solids mixture to be separated with a liquid medium of controlled density such as a suspension of magnetite of pre-determined concentration. The density of the liquid medium is chosen so that the lighter material of the mixture floats whilst the heavier component or components sinks. Either or both of the separated solids may be a desirable product of the process but, in the case of coal, where the density of the separating medium is typically between 1.35 and 1.45, the lighter 'floats' are the desirable high quality coal whilst the 'sinks' are low quality coal and impurities.
It is of particular advantage to provide facilities for dense-medium separation which may be moved between locations relatively easily. For example, it may be required to treat imported coal at or near the quayside to avoid the additional costs of transporting it to a treatment plant and thence to its final destination. Mobile dense-medium separation equipment is already available but has certain disadvantages arising from the fact that such equipment hitherto available uses a rotatable inclined disc for contacting the solids mixture with the separation medium. Such disc or wheel separators cannot provide efficient separation except at low throughputs of solids because the pool of liquid medium which can be used is relatively small. Consequently either the throughput must be kept low or the quality of separation judged to be acceptable must be reduced.
The present invention aims to overcome some, at least, of the disadvantages of prior mobile dense-medium separation apparatus by providing an apparatus offering a greater contact between the liquid separating medium and the solids to be separated.
According to the invention, a mobile dense-medium separating apparatus comprises a rotatable drum, arranged so that its axis is generally horizontal and having at one end an aperture through which solids and liquid may be introduced into the drum and at the other end an aperture through which solids and liquid may exit the drum, means to convey solids and liquid to and away from said drum, means to rotate said drum about its longitudinal axis and means to enable the apparatus to be readily moved between locations.
The rotatable drum may be mounted upon rollers which, upon rotation, effect rotation of the drum about its axis. Other means of rotation are also envisaged, such as a belt drive for example.
The drum preferably comprises a circumferential channel extending around approximately the centre of its length on the inner surface of the drum. The channel thus forms a continuous well around the inside of the drum. The cross-section of the channel is preferably rectangular with the top edges of the sides of the channel at the same level as and continuous with the sides of the drum, whilst the sides of the channel extend generally perpendicularly from the outer surface of the drum. The channel is preferably divided transversely along its length by a number of walls.
The inner surface of the drum on either side of the central channel is preferably divided by a continuous wall arranged around the inner surface of the drum in a spiral pattern and extending generally perpendicularly from the inner surface of the drum. The spiral wall on one side of the central channel is wound in the opposite direction to that on the other side of the central channel. Both of these walls are arranged so that, when the drum is rotated in a given direction, solids which have dropped between adjacent turns of a spiral wall are conveyed, as in an Archimedes screw, towards and into the central channel.
The means to convey solids to the drum preferably comprise belt-type conveying equipment. It is preferred that, especially for certain types of solids such as coal, the solids undergo a pretreatment before entering the drum. Such pretreatment may include sieving, washing and de-sliming, for example. The solids are then preferably flushed into the drum with the aid of some of the liquid separating medium to be employed in the separation process.
During the separation process, that is, as the solids and liquid medium are contacted together by virtue of the rotation of the drum, the fraction of solids material of greater relative density sinks to the bottom of the pool of liquid in the drum whilst the lighter fraction floats on the surface of the liquid. The "floats" are thus carried out of the barrel as the liquid medium flows out and are carried thence, preferably, by means of a moving belt conveyor. The aperture through which solids and liquid flow out of the drum is preferably larger than the aperture through which solids and liquid are admitted, so that the level of liquid may be maintained above the lowest part of the out-flow aperture, thereby ensuring that flow out of the drum occurs without recourse to pumps, etc. The "sinks" are preferably collected in a wide funnel or chute and conveyed out of the drum on a moving belt or, preferably, by flushing with more dense-medium liquid. The funnel or chute is preferably located within the barrel with its wide opening facing upwards and located beneath the central region of the barrel. Thus, as solids collect in the central channel, if present, they are carried with the rotation of the drum, preferably by means of the walls within the channel, if present, above the funnel opening, into which they fall under gravity.
The sinks and floats removed separately from the drum will usually each require to be separated from associated liquid. It is particularly preferred to carry out each such draining, and optionally rinsing, upon a vibratory screen, by means of which the separation may be conducted in a particularly compact manner. In one highly advantageous form of the invention, a single vibratory screen, with two separately partitioned sections, is used to carry out the two draining operations simultaneously.
The apparatus preferably comprises a means for recovering the dense-medium liquid used in the separation process. In the case of a magnetite - based dense-medium process, the recovery means preferably includes a magnetic separation process from which the magnetite concentrate recovered is returned to the dense-medium preparation area to be made up to a liquid medium of the required density. In this way the consumption of magnetite may be kept very small as it is recovered from the liquid-solids mixture carried over out of the drum.
The means to enable the apparatus to be readily moved preferably comprises a trailer which is adapted to receive the components of the apparatus in the positions which they occupy during normal operation of the apparatus. The components are preferably mounted upon parts of a framework of mounting members which is fixed to the bed of the trailer. Thus the trailer upon which the apparatus is situated may be towed to a location where it is desired to use the apparatus and the apparatus may be ready for use within a very short time. A supply of water and power must be provided at the location where the separation apparatus is to be used.
A preferred embodiment of the mobile dense-medium separating apparatus will now be described, by way of example only, with reference to the accompanying drawings, which are:-

Fig.1, a schematic diagram showing the processes and apparatus used in the dense-medium separation apparatus for washing coal, and
Fig.2, a perspective view of the apparatus of Fig.1.

In the illustrated apparatus, a coal feedstock is conveyed by a belt conveyor 10 on to a washing screen 11 where it is de-slimed. The washed coal mixture is then washed into the dense-medium separating drum 12 with some of the dense-medium separation liquid 19 employed in the drum. The liquid comprises a suspension of magnetite in water such that the relative density of the liquid medium is at a selected value between about 1.35 and about 1.45. The drum 12 comprises a protruding channel 13 located around the central part of the drum and dividing walls 14 and 15 which are arranged in a spiral pattern around the inner surface of the drum between each end of the drum and the central channel. The aperture 16 on the input side of the drum is smaller than the aperture 17 on the exit side of the drum so that the dense-medium liquid may flow out of the aperture 17. The drum 12 rotates about its longitudinal axis by means of rollers 18 upon which the drum is located.
When the coal mixture and liquid medium enter the rotating drum, they are contacted together by the rotation of the drum. That component of the mixture which is of lower relative density than the liquid medium floats upon the liquid medium as it flows out of the drum through aperture 17. The more dense component of the coal mixture sinks to the bottom of the drum, either into the central channel 13 or on to the wall of the drum between the turns of one of the spiral separating walls 14 and 15. These walls are arranged so that as the drum rotates, any solids which are engaged by either of the two walls 14, 15 are delivered into the central channel 13. Channel 13 is divided transversely by several separating walls 20 which carry the sunken solids around with the drum as the drum rotates. When such solids have been carried around to about the top of the path of rotation of the channel, they fall from the channel and separating walls into a chute 21 along which they are washed by another quantity of liquid medium from the pot 28.
The sunken solids, or sinks, from chute 21 and the solids which have floated out of the drum then pass on to a vibratory screen 22, which has a stainless steel wedge wire deck and is divided longitudinally, by means of a partition 33, the sinks being carried on one side of the partition and the floats on the other. The material on the screen 22 passes over a free drainage area 23 and then through an area 24 in which the solids upon the screen are washed, first with dense-medium liquid at 25 and then with fresh water at 26, before passing out of the apparatus to be collected and distributed or stored.
The dense-medium liquid which has drained from the solids is collected in tank 27 where it is made up to the correct density and then recycled to pot 28. The diluted liquid which has resulted from the washing process at 26 is concentrated in a magnetic separator 29 from which the concentrate is taken to tank 27 for make-up and then recycled to the start of the process.
The above apparatus is all mounted upon a trailer 30, shown in Fig.2 attached to a truck 31. The apparatus is mounted on the trailer in appropriate positions with the aid of mounting members 32 which support the apparatus at each location. Thus by towing the trailer 30 by means of the truck, the separation apparatus may be moved between locations easily so that it is suitable for use in situations where only a temporary separation facility is required.

Claims

A mobile dense-medium separating apparatus, characterised in that it comprises a rotatable drum (12), arranged with its axis generally horizontal and having at one end an aperture (16) through which solids and liquid may be introduced into the drum and at the other end an aperture (17) through which solids and liquid may exit the drum, means (10, 11, 21) to convey solids and liquid to and away from said drum, means (18) to rotate said drum about its horizontal axis and means (30, 31) to enable the apparatus to be readily moved between locations.
Separating apparatus according to Claim 1, characterised in that said drum (12) comprises a central channel (13) extending around approximately the centre of its length on the inner surface of the drum.
Separating apparatus according to Claim 2, characterised in that said channel (13) is of rectangular cross-section, the top edges of the sides of the channel being at the same level and continuous with the sides of the drum and the sides of the channel extending generally perpendicularly from the outer surface of the drum.
Separating apparatus according to Claim 2 or Claim 3, characterised in that said channel (13) is divided transversely along its length by a number of walls (20).
Separating apparatus according to any of Claims 2 to 4, characterised in that the inner surface of said drum (12) on each side of said channel (13) is divided by a continuous wall (14, 15) arranged around said inner surface in a spiral pattern, said wall (14, 15) extending generally perpendicularly from the inner surface of the drum.
Separating apparatus according to any of the preceding claims, characterised in that said means to convey solids to the drum comprises belt-type conveying equipment (10, 11).
Separating apparatus according to any of the preceding claims, characterised in that said means to convey solids away from the drum comprises a moving belt conveyor.
Separating apparatus according to any of the preceding claims, characterised in that the aperture (17) through which solids and liquid flow out of the drum (12) is larger than the aperture (16) through which solids and liquid enter the drum.
Separating apparatus according to any of the preceding claims characterised in that solids are collected within the drum (12) in a wide funnel or chute (21) located within the drum and conveyed out of the drum by flushing with liquid.
Separating apparatus according to any of the preceding claims characterised in that it further comprises a vibratory screen (22) whereby to separate the solids and liquid which are conveyed from the drum.
Separating apparatus according to Claim 10, characterised in that said vibratory screen comprises two separately partitioned sections whereby to separate each of two streams of solids and liquid separately and simultaneously.
Separating apparatus according to any of the preceding claims, characterised in that it further comprises a means (27) for recovering dense-medium liquid used in the separation process.
Separating apparatus according to Claim 12, characterised in that said recovery means comprises a magnetic separator (29) by which to remove magnetic material from said liquid.
Separating apparatus according to any of the preceding claims, characterised in that said rotatable drum (12) is mounted upon rollers (18) which effect rotation of the drum about its axis.
Separating apparatus according to any of the preceding claims, characterised in that said means to rotate said drum comprises a belt drive.
Separating apparatus according to any of the preceding claims, characterised in that said means to enable the apparatus to be readily moved between locations comprises a trailer (30) which is adapted to receive the components of the apparatus in the positions which they occupy during normal operation of the apparatus.
Separating apparatus according to Claim 16, characterised in that said components are mounted upon parts of a framework of mounting members (32) which is fixed to the bed of the trailer (30).