852 THE COLLIERY GUARDIAN. November 3, 1916. order to obtain a classification by density, it is there- fore necessary to screen the materials beforehand, on screens of suitable aperture, so as to have a classifica- tion by volume. Each grade of screened product is then placed in a trough of gradually diminishing slope, traversed by a current of water sufficiently fast to carry away the coal particles, whilst allowing the schists to settle down at the upper end, the intermediate pro- ducts rolling down over the deposited schists. On reaching each groove r, the water will divide into two branches, the one carrying the coal down the trough, whilst the other flushes the schists through the groove. Maximum efficiency would evidently be obtained if all the schists were removed in this way, without being accompanied by any of the coal; but, in spite of all precautions, there will always be some of the coal and the schist separated from the equivalent coal particles. These two influences in the Rheolaveur—the upward current and the stagnant zone—are most clearly mani- fested, and give the best results when the Rheolaveur operates by pulsation, through the valves being set in a suitable manner, and with attention to the quantity of schists to be removed. The consequence of this pulsation is a feeble upward current, interrupted by brief periods of stagnation, during which the influence of density prevails over that of equivalence. The upward current, after a lull, returns the separated coals into the trough of the washer without hindering the fall of the schists, which drop edgewise. The upward current has also a useful effect on the washing process after leaving the Rhdolaveur, its velo- groove Rheolaveur, with single discharge orifice for the schists (figs. 6 and 7). Multiple groove Rheolaveur, with separate discharge for- each groove. Multiple groove Rheolaveur, with auxiliary horizontal current from separating coherent particles (figs. 8 and 9). Coal Washery at Lens. The primary object of the Societe des Mines de Lens in installing Rheolaveurs Was to increase the output of the felspar washers. The plant was constructed to deal with 100 tons per hour of unscreened coal, containing 74 per cent, of 0/fin. (including 15 per cent, of 0/yi- in.); but was actually treating coals with as much as 82 to 90 per cent, of 0/f in. (including 25 per cent, of 0/g’Tin.). The Ateliers de Fives-Lille (makers of the Rheo- External View of Rheolaveur. (Fig. 6.) Fig. 7.—With Single Discharge. > 1 i I -■ ‘ ■ ► < Fig. 9.—With Auxiliary Horizontal Current. Multiple-groove Rheolaveurs. carried through with the schist, and therefore a loss, the prevention of which forms the object of the Rhdolaveur, which sets up an ascending current through the grooves, whilst allowing the schists to drop through. Every particle subjected to the action of the upward current, of velocity V, is acted upon by two forces : its own weight in water P = K,3 (d — 1) and the pro- pulsive effect J = K'jdiW2 of the current. The equation K, (d — 1) are in equili- brium, i.e., “ equivalent,” and ’therefore the upward current produces a classification of the same order as the current in the trough. The schists and coal entering the groove of the Rheolaveur are immediately acted upon by the upward current; and, given a suitable value of V, the schists city being compounded with that of the water in the trough, and both complementing the classifying action of the superior groove, and preparing the material for classification by the groove next below. In practice, it is found that the flow of water in the trough gives very satisfactory results, even when the coal has not been very carefully screened; and, in fact, the preliminary sizing of the coal does not need nearly so much attention as for washing in jig boxes. This need is still further reduced when the additional classi- fying effect of the Rheolaveur is taken into considera- tion. For example, if, for washing in box washers, slack with 15 to 20 per cent, of ash requires to be screened to 0/|, |/f, and f/fin., the Rheolaveur can produce equal results from 0/fin. slack, i.e., one size only is needed. The washing plant for treating coals by the fore-. laveur) proposed to mount a multiple groove Rheolaveur between the screens and the first washing boxes, in order to relieve the feed trough, and thus increase the total output of the washer. The colliery, however, preferred to try the Rheolaveur on the whole of the 0/f in. smalls. As the jig screens furnished two classes of smalls, 0/( in. and |/| in., each of the washers was fitted with Rheolaveurs, by merely altering their length and slope, and making other slight changes. The arrangement adopted was that shown in fig. 4, the second washing troughs originally contemplated, being rendered unnecessary by the satisfactory opera- tion of the first troughs. Time Tests.—Fifteen tests of 24 hours each were made with the felspar boxes, and 15 similar tests with Rheolaveurs—all treating the same class of material, the samples, analyses, and weighings being all made -A., ■ ® ' i' 11 n Fig. 8.—Multiple-Groove Rheolaveur with Separate Discharges. I Fig. 10.—Rheolaveur with Schist Conveyor. will drop down, whilst the coals are floated back into the trough, and carried away by the current there. This separation is very clean, the particles having already been classified by volume. The equivalent products, due to imperfect screening or other cause, are also washed by the Rheolaveur almost as perfectly as the already classified products. The explanation of this highly-interesting feature is as follows :—For the equivalent products to be separated by density when submerged in a liquid, their density alone must come into play, an effect obtained at the moment they drop into stationary liquid, and are opposed merely by the static thrust of the latter. By adjusting the velocity of the upward current in the Rheolaveur so that it counterbalances the downward current in the groove, a stagnant zone is produced at the top of the apparatus, the equivalent products in this zone being classified according to their density, going process comprises : A screen, classifying the material according to size, but not nearly so minutely as for box washing; a washing trough for each size fur- nished by the screen, and discharging, at its lower end, the whole of the washed coal; a set of Rheolaveurs attached to the grooves of each trough, and returning to the trough everything but the schists (fig. 3); under- neath each trough a second trough (and even a third one, if necessary), for re-classifying the mixed pro- ducts passed by the final Rheolaveurs of the first trough (fig. 4). The dimensions of the apparatus are as follow, the exact selection depending on the amount, nature, and ash content of the smalls to be washed :—Trough, 12 to 20 in. wide, and sloping at a gradient of 1 in 100 to 1 in 22; longitudinal distance between two Rheolaveurs, 8 to 9 ft. Simple Rheolaveur (fig. 5), length, 8in.; heigh over all 22 in.; width, to fit the trough. Multiple in the same manner. The washing was conducted in such a way as to obtain products identical in respect of ash content; and, in fact, the percentage of ash in the box washer product was 8'41 per cent., as com- pared with 8'36 per cent, in that from the Rheolaveur washers, the crude slack having respectively 14’52 and 14-95 per cent, of ash. The concordance of these figures emphasises the value of the result, which was that the Rheolaveurs extracted 8-728 per cent, of schists, as compared with 10'027 per cent, taken out by the felspar washers, the former thus effecting a saving of 1’3 tons of coal on every 100 tons of slack treated. The schists from the Rheolaveur contained 65-01 per cent, of ash. The apparatus was then tried in practice for a period of six months, during which time 2,000 tons of slack were treated per diem (24 hours), and a saving of 20 tons of washed slack per day was obtained. The