US2304352A - Separation of materials of different specific gravities - Google Patents

Description

Dec. 8 1942. F. L. GRIII=FITHSETAL ,304 2 SEPARATION OF MATERIALS OF DIFFERENT SPECIFIC GRAVITIES Filed Jan. 18, l940 INVENTORS:

ATTORNEYS.

W TNESSES: w I Franklouis firifiiihs 25a M FrederLck Charles Myer,

Patented Dec. 8, 1942 UNITED STATES PATENT OFFICE SEPARATION OF MATERIALS OF DIFFERENT SPECIFIC GRAVITIES deceased Application January 18, 1940, Serial No. 314,422 In Great Britain January 6, 1939 3 Claims.

This invention relates to improvements in the methods and apparatus for the separation of materials of different specific gravities, and in particular to the separation of coal from its impurities, by the Chance method described in British Patent No. 119,038 and U. S. Patent No. 1,224,138, granted May 1, 1917that is to say, the method in which the materials are introduced into a liquid mass or separation medium comprising a suspension of sand in a liquid (which is generally water, and is hereinafter so designated), which is so arranged that its effective density is great enough to cause some materials, such as coal, to float, while others, such as slates (hereinafter re ferred to as refuse") sink. There may, of course, be a layer of water on top of the liquid mass, to minimize loss of sand with the floats.

In U. S. Patent No. 1,392,400, which relates to the Chance method of separation, it has been proposed to provide, in the liquid mass in the separating vessel or chamber, horizontal zones or strata of difi'erent specific gravity or density, whereby in addition to the light material or "floats" and the heavy material or "sinks," intermediate products in the nature of middlings" may be obtained, these middlings" being extracted continuously by means of a screw conveyor leading the middlings" to an elevator whereby it is carried above the level of the liquid in the separating chamber, to be thereafter suitably screened or otherwise treated separately. In U. S. Patent No. 1,545,636, also relating to the Chance method, it has been proposed to intermittently withdraw intermediate products mixed with sand by means of a gate in the side of a cal complications and wear, and that it cannot be applied conveniently to a separating vessel of circular horizontal sectionalthough the screw conveyor within the chamber may serve a useful purpose in assisting agitation of the liquid mass to maintain the sand in suspension.

An object of the present invention is to provide an improved method and apparatus for carrying out the Chance process which is not subject to these disadvantages.

According to the present invention, the separating vessel or chamber that contains the separation medium or liquid mass (comprising a su.s pension of sand or the like in a liquid) is pro vided with mechanical or other agitating means and with hydraulic jets which not only serve to maintain the sand or the like in suspension in the liquid, but also provide a plurality of zones of difierent specific gravities in the liquid mass. Discharge or outlet means in the region of at least one such zone below the uppermost one are arranged so that in operation middlings floating in or on this zone of relatively high specific gravity (as compared with the liquid mass above) are discharged through said outlet by said agitating means, and are lifted in a discharge duct or ducts communicating with said outlet to a suitable level for discharging said middlings." The hydraulic jets may be arranged to assist in directing the middlings into the outlet; or other water jets or suitable means may be provided for this purpose. Hydraulic jets (i. e., sand and water or water jets) and/ or mechanical means may be provided in the duct or ducts for lifting the middliugs; and, preferably, an adjustable weir is provided at the top of the discharg duct(s)or at least one of such ductsfor varying the head of the liquid mass in the duct or ducts.

The separating vessel or chamber may be of any suitable shape or form, and may be of circular horizontal section. In the form of apparatus hereinafter described, a mechanical agitator is arranged to rotate about a vertical axis in the liquid mass, and the discharge or outlet means comprises one or more tangential outlets communicating with the discharge duct or ducts and suitably arranged relative to the direction of rotation of the agitator (i. e., opening out through the peripheral vessel wall in the direction of rotation produced at this intermediate level of the liquid mass), so that the middlings, which are directed by the agitator to the wall of the separating chamber, are discharged into the said duct or ductsfor removal and subsequent treatment. In other words, the agitator may be made to not merely agitate the liquid and keep the sand in; suspension, but also to rotate the mass at the intermediate level at suilicient velocity to cen-, trifuge to its periphery the intermediate material floating in this zone, while the heavier material is allowed to sink through said zone. As already mentioned, sand and water jets, or water jets, and/or mechanical means may be introduced into the said duct or ducts to assist in lifting the "middlings.

That the heavy material should thus sink right through the zone below the top one-instead of mostly or largely discharging at its peripheral outlet, along with the middlings, by centrifugal action-is explained (1) by the fact that in falling through the top zone where the specific gravity of the fluid mass is the lowest, the heavy material acquires much greater velocity than does the (lighter) middlings; and (2) by the fact that at the zone whose specific gravity corresponds to that of the middlings, the middlings necessarily lose all their velocity, whereas that of the heavy material is maintained or even augmented. Accordingly, the accumulated momentum of the falling heavy material carries it very quickly past the middlings outlet, before the centrifugal force there can deflect it materially.

The middlings" thus separated both from the coal, which remains floating at the top of the separating vessel, and from the refuse, which is withdrawn at the bottom of the separating chamber, may pass from said discharge duct or ducts on to the desanding and drainage screen used for the floats, suitable barriers being provided on the screen for maintaining the separation of the materialsor, of course, they may be desanded and drained on a separate screen.

One arrangement of apparatus for carrying out the Chance process in accordance with the invention will now be described by way of example with reference to the three figures of the accompanying drawing, in which Figure 1 shows a part longitudinal section; Figure 2 shows a plan of the apparatus; and Figure 3 shows a part longitudinal section of apparatus having mechanical means for lifting the middlings" in the duct.

Referring now to Figures 1 and 2 of the drawing, the separating chamber comprises a vessel I of inverted conical shape having a cylindrical top portion 2 which is provided with the usual overflow weir 3 through which pass the floats. A discharge chamber 4 is provided at the bottom of the vessel, for discharging the refuse from the vessel. At a suitable position or level intermediate between the weir 3 and the discharge chamber 4, and preferably (as shown) in the conical portion of the vessel I, there is arranged a tangential outlet 5 communicating with an upward directed pipe 6 which terminates above a chute 1 leading to the main desanding and draining screen 8 for the floats from the weir 3-the said screen 8 being divided by a partition 9 so that the floats" and the middlings" are discharged from said screen separately.

Water is introduced through jets I4 in the side of the vessel l at three different planes or levels, two below and one above the said tangential outlet 5. The quantities of water introduced at these planes are so arranged or determined that the density of the liquid mass in the vessel becomes progressively (but not necessarily uniformly) greater from top to bottom. Thus for example it may be arranged that the density in the zone above the top plane is about 1.45, while in the intermediate zone between said top plane and the next lower plane it is about 1.75, and in the zone below the bottom plane the density is greater than 1.75.

Rotation of the liquid mass is effected to a great extent by an agitator comprising a shaft I0 and stirring arms ll, mounted to rotate about a vertical axis, and the agitator is arranged so that materials sinking through the liquid mass are directed to the side of the vessel. The arms on the agitator are positioned so that the "middlings (that is to say, those materials which are of a specific gravity intermediate between the "low or coal gravity and the high or refuse gravity) are directed into the tangential outlet 5 and up the pipe or duct 6 attached thereto, In the outlet 5 and the pipe 6, a number of suitably directed sand and water or water jets l2 are provided to assist in conveying and raising the middlings to the chute l which directs them on to the screen 8. At the termination of the pipe 8, an overflow weir I3 is arranged, and is provided with suitable means of adjustment so that the hydraulic head of material and liquid in the pipe 6 can be balanced against the corresponding head of material and liquid in the vessel l above the outlet 5. As shown, the vertically movable weir I3 is attached to slotted guide bars l6, one at least of which may be clamped to a side wall of the weir-box by a clamp-bolt arrangement ll. The balanced conditions thus obtained substantially prevent the liquid mass in the vessel I from flowing out of the outlet 5, so that the upward currents of agitation are maintained, and the sand is kept in suspension to form the zones of varying specific gravity.

Mechanical means for lifting the middlings may be provided in the pipe 6, in addition to or in place of the sand and water or water jets l2. The mechanical means may comprise an elevator l5 in the pipe 6, as shown in Figure 3 of the drawing.

While the invention is particularly designed for the cleaning of coal, it may be applied to the separation of other materials which are separable by the Chance process, and the word coal" used herein is intended to include such materials. The term liquid mass we desire to be understood to include any mixture of comminuted solids and liquids which when properly agitated will approach the properties and fluidity of a liquid; the term water" is intended to mean any liquid suitable for making a liquid mass of the described type; and the term sand" is intended to designate any comminuted solid insoluble or substantially insoluble in the liquid used and suitable for making a liquid mass of the described type.

Having thus described our invention, we claim: 1. An improved process of separating heavy. intermediate and lighter materials by means of a liquid mass of sand or the like maintained in suspension in and by an upfiow of liquid, which comprises supplying upflowing liquid to the liquid mass at various levels so as to maintain therein stratified zones of various different densities, in the upper and intermediate of which zones the lighter and intermediate materials respectively float and are thus arrested and segregated, while the heavier material sinks through; discharging the lighter material at the top of the liquid; rotating the mass in the zone of intermediate density at sufficient velocity to centrifuge to its periphery the intermediate material arrested in the zone as aforesaid; continuously expelling the centrifuged intermediate material from the periphery of said intermediate zone; and subjecting the expelled intermediate material to fluid current action to lift it through a segregated portion of the liquid mass outside the field of rotation for discharge at the level of the liquid in said segregated portion.

2. Apparatus for the separation of heavy, intermediate and lighter materials by means of a liquid mass of sand or the like maintained in suspension by an agitated upflow of liquid, in which mass the lighter of the materials which is to be separated floats at the top while the rest sinks lower in the mass, said apparatus comprising a separating vessel having a discharge for the lighter material at its top, a discharge for the heavier material at its lower region, and an outlet for the intermediate material at an intermediate point; an open conduit in constant communication at its bottom with the vessel and leading upward from the outlet substantially to the level of the top of the vessel; means for supplying upfiowing liquid to the mass at various levels, so as to maintain the liquid mass in the vessel in stratified zones of various different densities; agitating means for maintaining the sand in suspension in the liquid in said zones and for rotating the mass in the zone of intermediate density at sufficient velocity to centrifuge to its periphery intermediate material sinking to this zone and remaining there, while the heavier material sinks therethrough, and for causing centrifugal expulsion of the intermediate material through said outlet and into said conduit; and fluid current means operative to elevate the intermediate material in said conduit for dis charge from the top thereof.

3. Apparatus for the separation of heavy, in-

iermediate and lighter materials by means of a liquid mass of sand or the like maintained in suspension by an agitated upfiow of liquid, in which mass the lighter of the materials which is to be separated floats at the top while the rest sinks lower in the mass, said apparatus comprising a separating vessel having a discharge for the lighter material at its top, a discharge for the heavier material at its lower region, and an outlet for the intermediate material at an intermediate point; an open conduit in constant communication at its bottom with the vessel and leading upward from the outlet substantially to the level of the top of the vessel; means for supplying upfiowing liquid to the mass at various levels. so as to maintain the liquid mass in the vessel in stratified zones of various diiTerent densities; agitating means for maintaining the sand in suspension in the liquid in said zones and for rotating the mass in the zone of intermediate density at suflicient velocity to centriiuge to its periphery intermediate material sinking to this zone and remaining there, while the heavier material sinks therethrough, and for causing centrifugal expulsion of the intermediate material through said outlet and into said conduit; and jet means at various points along the conduit operative to elevate the intermediate material in said conduit for discharge from the top thereof.

FRANK LOUIS GRIFFITHS. FREDERICK CHARLES MEYER.

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