US2141451A - Apparatus for the pneumatic separation of materials of different specific gravities and sizes - Google Patents

Description

2,141,451 APPARATUS FOR THE PNEUMATIC SEPARATION OF MATERIALS Dec. 27, 1938. F. F. RIDLEY OF DIFFERENT SPECIFIC GRAVITIES AND SIZES ZYSheetS-Sheet 1 Filed June 1, 1936 2,141,451 APPARATUS FOR THE PNEUMATIC SEPARATION OF= MATERIALS Dec. 27, 1938. F. F. RIDLEY OF DIFFERENT SPECIFIC GRAVITIES AND SIZES 2 sheets -she t 2 Filed June 1, 1936 Patented Dec. 27, 1938 UNITED STATE 3 PAT EN'T OFFICE APPARATUS FOR THE PNEUMATIC? SEPA- RATION or MATERIALS OF DIFFERENT! sPEomIc GRAWIT-IES- AND SIZES/ Frank Frost Ridley, Rutland Park, Shefl'ield,

England, assi'gnor to Colliery Engineering Limit'ed, Yorkshire, England, a British joint-stock company Application June 1, 1936, Serial No. 82,998 InGreat Britain June- 5, 1935 6 Claims. (01. 209-44) This invention comprises improvements in apparatus for the'pn'euma'tic' separation ofmaterials ofdifferent specific gravities and sizes, such' 10 of separating such materials according to Patent No. 1,843,405 issued to George Raw on February 2,.1932, which relates to the use of static pneumatic pressure to achieve stratification between materials of different densities, but without regard to the sizes of the particles. This latter process is of particular usefulness in the treatment of fines, because it eliminatespre-sizing, which is especially difficult andtroublesome in the finer sizes.

The separate pneumatic treatment of very fine sizes, as compared with the'larger material such as up to 1" or 2",. has presented difficulties mainly owing to the muchslower rate of stratification and the greater sensitiven'ess of the bed of. materials to the pneumatic conditions applied to it. The slower rate of I stratification of fine materials makes it desirabletooperateon a relatively thin bed of materials and' also to provide a considerable length of table over which the materials have to pass and thus a considerable period of treatment, inorder to ensure efficient purification. However, the greater sensitiveness of the bed whenworki'ng with thin beds of fine materials, for example beds from 1" to 2" thick, imposes conditions of delicacy requiring accurate control in order to maintain, during the full period of stratification, the proper condition of balance and fluidity which is necessary 'forstratification in the bed ofmaterials. 40 As aresult, it is found that there are practical limits to the length and areaof bed which can be separately maintained in the properand uniform condition required for stratification. If it is attempted to work with too great'an area, it is found that, owing to inevitable variations in character of the materials, one part: of the bed may be liable toburstunder the influence of the pneumatic pressure and destroy stratification which has already taken place.

In dry cleaning tables, the stratification'of the materials and the separation of the layers one from another usually proceed concurrently and, in many cases, certain quantities'of' the coal or other less dense material are discharged progressively. as they become freed of the denser It is also of particular utility in carrying out the process material or impurities, whilethe latter, such as concentrated shale or stone, progresses to the end of the table. However, with fine materials, owing to the slower stratification, this does not provide the best opportunities of completely puri- 5v fying the coal. It is better to arrange for the coal or the like to pass over asnearly as possible the whole length of the table before discharge, thus subjecting it to-the cleaning influence for the maximum'period. 10-

In some dry coal cleaning tables,- attempts have been made to secure the advantage of this long treatment byemploying variousmeans for extracting the stratified shales through the deck or table surface and allowing the coal to passon 15 to the end, but difficulties have usually been associated with these discharge means. In the first place, it has been'found that the fluid condition of a bedof' fine materials-on a long table ordeck causes it to assume different thicknesses. This 20 disturbance of the conditions of the bed upsets the stratificationso that it is diflicult to obtain effective discharge of theshale. In the second place; if' the lower stratum bedischarged' directly from a slot device disposed transversely of- 25 the table, a large area will be provided suflicient for the undesired discharge of coal with shale. In additionpneumaticpressureis-liable to escape violently through the slot instead of going through the bed: If, in order to avoid these de- 30 fects, the slot be connected'with a shale chute having intermittently operated means for discharging shale, the bed isdisturbed by the intermittent action ofsuch means.- Alternately if the escape ofair is avoided by disposing the slot 35 in animpervious part of the table the portion of the bed in the neighbourhood of the slot is unsupported by pneumatic pressure and the bed will notice maintained in the desired fluid condition.

Finally, means fo'rshaving off :the' lower stratum 40,

anddischa'rgingit througha slot are liable'to-disadvantages owing to the fact that the shaleoccu pies'only a" relatively thin" layergand the irregular shape of the particles-produces an ill-defined line of demarcation between thestrata 45 The principal object of the present invention is to provide an iii'iprov'ed construction: for the efficient separation of fine materials on a" long table, while avoiding: undesirable fluctuations" in thickness of the bed and providing for the dis- 50 charge of the bottom: layer in such a manner as toprevent undue disturbance of the fluidconditions-ofthe-bed; I I V According-to this invention atable on deck dis-- posed over an air box: is dividedlnto a=number of 55 stratifying ones by transverse slopes or steps, and

discharge of the lower stratum of materials is effected in a restrained manner, so as not to disturb the fluid conditions of the bed, by sieves, in the table disposed at the forward end of the zones. The division of the table by the slopes enables zones of predetermined area to be provided for ensuring proper control of the stratification conditions and for avoiding irregularities in the bed; Thus the table is divided into a number of zones or areas of a size not too large for proper control of the conditions, and before any irregularity is able to occur the stratification in one zone is completed, a part of the shale is discharged and the bed is re-formed for further treatment in the next zone. The coal is thereby subjected to a prolonged treatment in the succeeding zones and the shale is discharged without I disturbing the conditions in the bed. In the ab. sence of the slopes, the fluidity of the bed would cause it to run away at some points and build up at others; The re-formation of the bed in succeeding zones avoids this disadvantage.

The sieves are adapted for an effective discharge of the shale while preserving the uniform fluid conditions. The pneumatic pressure is able to pass through such sieves at all times owing to the disposition of the table over a single air box. The sieves are suitably provided by narrow transverse portions having perforations considerably larger than those in the deck and slightly larger than. the size-of the, largest particles treated. These sieves enable the shale to be discharged in a restrained manner without in any waydisturbing the conditions of the bed, the effect being to allow the lower surface ofithe shale layer to be discharged, in contradistinction to the discharge of the whole of a lower layer as in the case of an uncontrolled slot discharge.

In order to enable the invention to be readily understood reference will be made to the accompanying drawings, illustrating by Way of example, different constructions of apparatus for carrying the invention into effect, in-which draw:

1ngst Figure 1 is a side elevation with parts in section of one construction of apparatus in which the table is provided with sieves for discharge of the shale.

Figure 2 is a plan of Figure 1, with the dust hooding over the table removed.

Figure 3 is a section, to an enlarged scale, on the line III-III, Figure 2. V. Figure 4 is a section, to an enlarged scale, on the line IV-IV, Figure 2.

Figure 5 is a diagrammatic view construction.

of a modified Figure 6 is a plan view of the forward end of a modified construction of table, and V V Figure '7 is a central longitudinalsection of Figure 6. f

Referring to Figures 1 to 4, the apparatus comprises a rectangular table a of trough form with a perforate deck I), and upstanding sides 0 to maintain a given thickness of. bed. The deck is divided into a number of stratifying zones or cells A, B, C, arranged at .difierent relative levels,

each one being lower than the one preceding it. The forward end of one zone is connected with the rearward end of the next zone by an im- 1 through; the remaining sieves.

connected to any suitable conventional vibrating mechanism to give'a small throw at high periodicity. The table is slightly declined from the feed end a to the discharge end a to secure progression of the materials by gravitational flow. Other vibrating mechanisms can be applied as alternatives, and if they provide a component which causes forward progression of the materials, the forward declination of the table will naturally be decreased. Pneumatic pressure is supplied by a fan 71. through the duct 1' and pulsator 7 to the air box It. Aflexible connection k is provided between the table and the air box. Dust hooding 1 maybe provided over the table, any suitable means being employed for separating or settling the dust. The manner of supplying the pneumatic pressure isdescribed and shown in patents issued to George Raw: No. 1,730,947, dated October, 1929; No. 1,811,026, datedJune 23, 1931; and N0. 1,843,405, dated February 2, 1932. V

In operation, the raw materials such as coal fed tothe table at a flows in the manner of a liquid, under the influence of vibration and pneumatic pressure, the shale or the like gradually stratifying at the bottom of the bed. At the end of the'firstzone A, a certain amount of Stratified shale has collected at the bottom of the bed, and this riddles through the sieve e. The partially cleaned coal or the like flows down the imperforate slope d and issubjected to further stratifying action in the next zone B, further shale or stone being discharged through the sieve of this zone. The treatment proceeds similarly in the next zone. 7

By dividing the deck into several zones or compartments with 'imperforate slopes between them, the tableis divided into a'number of stratrestrained discharge action to be obtained, only part of the layer of shale beingpassed through any particular sieve. Only a thin stratum of the lower layer is discharged through any particular sieve. A protective layer of shale may thus be provided between the coal and the discharged shale, so as to prevent mixing and loss of coal in the shale. The, present invention provides a'progressive discharge'of shale the'heaviest and most easily'stratified passing through'the first sieve s and progressively lighter shale passing In order to en-' sure discharge of completely clean coal at the forward end of the table, some coal may be allowed to beldischarged with'the last vestiges of shale passing through the final sieve; The prodnot passing through this particular sieve would be principally middlings and could be extracted from the air box -]c by independent discharge means and re-fed to the table f rre-treatment with the raw'material. Sucha re-feeding will usually provide sufiicient' margin tocompensate for variations in the quantity of. shale in the raw feed. If desired, however, a further ad'- J'ustment may be provided by arranging for one or more of the sieves to be put out of action by plates having perforations of the same size as the perforations in the main deck. For example as shown in Figure 3 closure plates m may be fitted under the table a on hinges n so that the plate can be swung clear of the sieve e (as shown in dotted lines) by a lever device 11. on the side of the table. The plates m can-be swung upwards to obstruct the sieves when desired.

Instead of allowing the coal to be discharged directly from the stratifying zone C, while the.

middlings and remnant of coal are discharged through the sieve; e, the particular arrangement illustrated may be adopted. In this arrangement provision is made for a. sharper final separation between-the last portion of stone extracted and the middlings which would otherwise pass into the air box k withthe stone. Thus over the imperforate slope d ofv the last zone there may be disposed a skimmer. or cutter. o. This skimmer, which may be vertically adjustable, divides the strata of the bed, middlings passing underneath the skimmer being diverted. by deflectors 0 into a central channel p having a perforated bottom. Above the skimmer plate 0 are provided deflectors 0 which divert the coal flowing over. the plate into side channels disposed alongside the central middlings channel 1). The bottoms of the coal channels 29 are normally blank, but may be provided with perforations if. desiredto permit of the air passing throughthe material to assist its passage to the end of the table. When perforated. a. further. cleaning; may take place in these channels, which are then provided with discharge slots at their forward ends to discharge any last vestiges of. impurities. Such material discharged throughtheslots would. contain coal and would be passed into the middlings for retreatment. The slots in this case would be beyond the end of the air box so that the material can be passedinto the main middlings chute.

In the channel p the middlings are subjected to a further stratifying action. A second coal skimmer plate q. is provided at the end of the channel, the deflectors q diverting coal into the sidechannels 11 while the middlings pass underneaththe plate into. a short zone 1'. The clean coal is discharged from the channels 10 into chutes s. As shown in Figure 4 the zone 1 is extendedv a short distance beyond the end of the air box is to allow the middlings to discharge into a middlings chute 1 beyond the clean coal. If the bed weretoo sluggish however a small extension such as a pipe and a small box, connected to the air box could be provided for supplying air pressure also to the forward portion of the zone 1. A skimmer plate t is provided at the forward end of the zone 1. Shale passes under this skimmer to a discharge outlet u, while the upper stratum of middlings passing over the skimmer is diverted laterally by deflectors A flap device '0 directs the middlings either into the outlet r so that they may be re-fed to the table, or into the outlet s for theclean coal. The two positions of the flap device, which is adjustable by a handle 0 are-shown in dotted lines, Figures 1 and4.

In order to maintain even thickness of bed in the zones, small-dams 10, Figure 4 may be fitted just: forwardly: of thesievese andiacross. the .full 7 width of the deck for-retaining the bed at given thickness. These damsare, as shown, only veryshort, as the thin beds have very little tendency to minor break away as they pass. over the slopes between the cells. The dams must not be too deep or they would tend to cause the bed to pile up and thicken and thereby destroy the regularity of the bed conditions. The dam may alternatively be in.the form of a blade 1:, Figure 3, which also serves for maintaining separation of the layers after discharge of impurities through the sieve e. The blade is disposed horizontally above the sieve and is connected to a somewhat wider blade m disposed above the slope d at approximately the same inclination. One or both of the blades :11, :1: may be adjustable for varying their inclinations. The horizontal blade at serves to dam the forward flow of materials and thereby maintain an even thickness of bed, while the inclined portion 90 serves to preserve on the next zone the Stratification obtained in the preceding zone, since it will be realized from Figure 3 that the denser materials flow under the blade and the less dense materials flow over it.

The shale discharged through the sieves e falls into the air box k, Figure 1, and may be extracted therefrom by any suitable means incorporating an air-sealed discharge. For example, the shale may be discharged into a small enclosed hopper y fitted with a balance valve y at the bottom to retain a given level of material inthe hopper. A screw conveyor 2 disposed along the bottom of the air box feeds the shale into the hopper.

According to the modified arrangement shown in Figure 5 the table comprises three stratifying zones, although four or more may be employed, each zone having a sieve discharge at its forward end. In this arrangement shale or the like discharged through the sieves l8 falls through the air box 70 and is discharged from hoppers l9 formed in the bottom of the box beneath the sieves. Middlings fall from the final sieve is through the air box to a third hopper I9 The hoppers are fitted with automatic discharge valves I So under constant air-lock conditions, conveyors being disposed beneath the hoppers for carrying the material away. Clean coal flows over the forward end of the table to discharge. Additional hoppers would be provided in accordance with the number and position of the bottom discharges provided in the deck.

According to the modified arrangement shown in Figures 6 and '7, the shale and middlings are separated at the end of the central trough or channel 2| by the adjustable skimmer or cutter 22; The middlings pass over the skimmer to a chute 23 and the shale passes beneath to another chute 24. The two chutes 23, 24 are in line with the central channel 2! just beyond the air box.

In normal circumstances, the sides of the table are parallel and of constant width, but under some conditions it may be found desirable slightly to vary the widths of the cells. The purpose of this is to accommodate variations in the rate of flow of materials, which sometimes is liable to occur with fine material of the kind in question, and may be caused partly by the removal of shale. Variations in width, however, are only slight, and may be suitably provided for by fitting strips or distance pieces to the insides of the walls of any particular section. Suchvariations in the widths of the cells are not for the purpose of varying the thickness of the bed but for the purpose: of maintaining it .atzuniform thickness when a tendency to thinning might otherwise occur, due to an increased rate of fiow at one portion.

It will be seen that the whole object is to make practically the whole length of table available for cleaning the coal, while at the same time extracting the shale progressively as it becomes stratified, and without in any way'interfering with the conditions of stratification. The sieves do not cause any tendency for the air pressure to be violent at these points, becausethe discharge is restrained and the stratified shale lies in a heavy bed upon them and prevents any such free flow of air. Also, when working under the static pressure condition, the size of discharge slots or perforations has very little effect, because the quantity of air flowing is negligible.

The improved tables are of particular advantage incarrylng out the static pressure process of separation already referred to. They may be operated singly orin multiple or pairs. Two or more tables may be arranged side'by side on one frame'or chassis and provided with a common air box or chamber or separate air chambers or each of several separating units may comprise multiple tables side by side, for example in the manner described in patent application Serial No. 643,258 now Patent No. 2,100,670, issuedto George Raw on November 30, 1937. One fan may be used to serve several tables or to serve several units each comprising several "tables, connection betweenithe fan and the air boxes or chambers being by branched pipes or otherwise and the pulsators of the several tables being set so as to give sequential pulsations through the several air boxes or chambers, where necessary, to' preserve uniform load on the fan,

as in Patent No. 2,100,670 above noted. In the case of tables placed in multiple side by side on' a single chassis, the invention'provides the advantage that all the less-dense materials are discharged at the forward end of the chassis and no side discharges are necessary. This enables the two or more tables or decks to be built adjacently and close together andonly a partition ora single side wall need be used to divide one deck from another. As large a table as desired, within mechanical limits, can thus be built without departing from the best size'of always been found the most difficult material to treat on pneumatic dry cleaning tables.-

I claim:

1. Apparatus for the separation of materials of different specific gravities by stratification of the materials due to pneumatic pressure, comprising an air box, a table having a pervious bottom disposed over said air box, a number of impervious slopes extending transversely of the table to provide a number of stratifying zones at different levels, sieves "for the discharge of the lower stratified layer disposedinthe pervi'- ous bottom at the forward'end of each zone, and controllable means adjustable for shutting off discharge through said sieves. J a

2. Apparatus'for the separation of materials of different specific gravities by stratification of the materials dueito pneumatic pressure, comprising an air box a table having a pervious bottom, disposed over'said airbox; a number of.

impervious slopes'extending transversely of the table 'to provide a number of stratifying zones at different levels, narrow sieves for the dis-' charge of the lower stratified layer disposed in the pervious bottom at the forwardend of each zone and having perforations larger than those in said bottom, closure plates having perforations approximating to the size of those in the bottom, and means for adjusting said plates for obstructing the discharge of materials through said sieves into the air box. 7

3. Apparatus in accordance with claim 2, comprising pivotally mounted closure plates and handles external of the air box for adjusting said plates; A v

4 Apparatus for the separation of materials of different specific gravities by stratification of the materials, comprising an air box, a table disposed over said air box and having a stratification zone with a fiat pervious bottom, means for maintaining a bed of materials of substantially even thickness on said zone, means for subjecting the bed to the influence of static pneumatic pressure for -maintaining the bed as a whole in 'equilibriumwith said pressure to inducea state of fluidity in the bed with the minimum escape of air therethrough and'a narrow discharge sieve disposed in the pervious bottom across 'thewidth of the table at the for- 5 ward end of the stratifying zone, said sieve being in pneumatic communication with the air box and having perforations larger than those in the pervious bottom and at least as large as the. largest particles of the lower stratified layer of materials for riddling the lower layer into the air box at the end of the stratifying zone while the less dense materials stratified. by' said pneumatic pressure occupy the upper layer, due to the maintenance of the 'fiuid conditions above the said sieves during the discharge therethrough of' material from the lower stratified layer.

. 5,Apparatus for the separation of materials of different specific gravities by stratification of the materials, comprising pneumatic chamber apparatus, a table having a pervious bottom disposed over said pneumatic chamber apparatus, impervious slopes disposed at intervals transversely of the table to divide it into'a num-. ber of stratifying zones at successively lower levels the farther they. are disposed away from the feed end of the table, means on said table for maintaining a bed of materials of substantially even'thickness thereon, means for subjecting the bed to the influenceo'f static pneumatic pressure'for maintaining the bed as a whole in equilibrium with said pressure to induce a state of fluidity in the bed with theminimum escape of air therethrough and a narrow discharge sieve disposed in the pervious bottom across the width .of the-table at the forwardend of each stratifying zone, said sieve being in pneumatic communication' with said pneumatic chamber appa ratus and having perforations larger than those in the perviou's'b'ottom and at least as largeas the largest particles of the lower stratified layer for theiriddling of the lower layer into the pneumatic chamber apparatus at the completion of "the'stratification in each zone while the less dense materials stratified by said pneumatic pressure. occupy. the upper layer, due to the' V maintenance of "the fluid conditions, above the said sieves during. the discharge therethrough of material from'the lower stratified layer.

r 6. Apparatus :for the separation 'of .materials of difierent specific gravities by stratification of the materials due topneumatic pressure, comprising an air box, a table having a pervious bottom disposed over said air box, imprevious slopes disposed at intervals transversely of the table to divide it into a number of stratifying zones at successively lower levels away from the feed end of the table, means on said table for maintaining a bed of materials of substantially even thickness thereon, a narrow discharge sieve disposed in the pervious bottom across the width of the table at the forward end of each stratifying zone, said sieve continuously allowing the application of pneumatic pressure to material over it and having perforations larger than those in the pervious bottom and at least as large as the largest particles of the lower stratified layer for the riddling of the lower layer into the air box at the completion of stratification in each zone, blades disposed over said sieves for dammin-g the flow of materials over the table and blades disposed over the slopes at approximately the same inclination for preserving in the next zone the Stratification obtained in the preceding zone. 1

FRANK FROST RIDLEY.

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