• April 14, 1916. 705 THE COLLIERY GUARDIAN. ________________________________________________________________________________ properties of sodium bicarbonate and its efficiency will meet this objection; moreover, if the effect were mechanical, still smaller percentages of quenching materials would probably be required. No experiments were carried out with incombustible or combustible gases in the apparatus; but, presumably, this could be accomplished by mixing the gases to be applied with the blast of air blowing the dust over the igniting medium. Nothing is said at present with regard to the difference between the coals. The figures given in the paper are only approximate, and must not be taken as exact. The curve (fig. 1) shows the relation between the specific heat and the critical percentages for one of the coals. The hydrated quenches all lie on the same side of the curve, but off it in such a way that their critical percentages would be, much smaller if these bodies retained their original compositions and specific heats over a long range of temperature. No correction is here introduced in the curve for thermo-chemical heat absorp- tion; and this may explain the anomalous position of tli-e hydrated quenches, or their anomalous position may be due to an over-estimate of the specific heat effect of added wafer. Supplement (Fig. 2). Lime was found to be one of the least effective of the quenching substances, and. the supplementary table Na2CO3,* 5H2O N< i2SO4; 6H2O |Nc i hco3 i t \ L : 1*. a2CO3 ' * \ \.Mg DO3Alb 1. * \ ..CaS \ □4,2H J 2o \ ■ ’B. CaO03 X ,CaO_ O 0-2 0-4 0-6 0-8 VO CRITICAL PERCENTAGES. Fig. 2.—Curve showing the Relation, for one of the Coals Tested, between the Specific Heats and the Critical Percentages based on Lime as a Unit. shows the values calculated (in lime as a unit) for the relative weights of materials required, the lime unit being, of course, different for the different coals :— Coal ................. Boiler ashes ............ Quicklime ............ Ground shale .......... Chance mud ........... Gypsum .............. Magnesia ............. Magnesia alba (levis) ... Anhydrous sodium car- bonate ........... Soda crystals ......... Sodium bicarbonate ____ Glauber salts ......... Proportion of coal ..... A B C D 1-32 ... 1-22 ... 1-18 ... 1-17 1-00 ... 1-00 ... 1-00 ... 1-00 0-75 ... 0-72 ... 0-71 ... 0-69 0-66 ... 0-58 ... 0-56 ... 0-54 0-5 ... 0-45 ... 0-46 ... 0-44 0-42 ... 0-47 ... 0-44 ... 0-39 0-28 ... 0-27 ... 0-23 ... 0-23 0-156... 0-15 ... 0-19 ... 0-14 0-105... 0-091... 0-10 ... 0-07 0-11 ... 0-13 ... 0-13 ... 0-10 0-09 ... 0-087... 0-10 ... 0-07 1-00 ... 1-22 ... 1-32 ... 0-82 _______________________________ Shipments of Bunker Coal. — The quantity of coal, etc., shipped for the use of steamers engaged in the foreign trade during March was 1,037,384 tons, as against 1,300,467.tons in March 1915, and 1,689,304 tons in March 1914. The aggregate so shipped during the three months ended March 31 was 3,273,224 tons, as compared with 3,978,631 tons in March 1915, and 5,035,448 tons ,in March 1914. American Coal Trade Conditions.—A sweeping enquiry into the bituminous coal industry of the United States is about to be undertaken by the Federal Trade Commission. Special attention will be paid to the effect of the Federal anti-trust laws on the soft coal industry. The investigation was decided upon as a result of representations made to President Wilson that Federal attention should be directed to conditions that obtained in the Indiana-Illinois coal fields. It was stated to the President that wastage in mining is enormous, that profits are small, and that something should be done to establish the industry on a basis where miners and operators might derive more substantial benefits. Enquiries made by the Commission showed that the con- ditions complained of are not peculiar to Indiana and Illinois, but exist also in the mines of Pennsylvania, Ohio, Colorado and other States. In the statement to the President relative to conditions in the Indiana-Illinois coal fields, it was set forth that their product is sold in 18 States, and that as a result of the anti-trust law in prohibiting co-operation among owners overhead costs eat up profits and react on the miners. “The effect of the United .States anti-trust law is to cause them to compete without restraint,” the statement continues, “ and'this unrestrained competition has yielded a decreasing selling price.” It is said also that the State laws which were enacted to assure the safety and social welfare of the miners have resulted in increased production costs. “The effects of-these two sets of laws have moved in opposite directions,” it is said. “ The rising cost of production and the falling selling price have long since made profits impossible, and now threaten the safety of the whole business structure as well as the miners and the people. One of the refinements of competition in which these operators have engaged has been the erection of elaborate plants with which to prepare and clean carefully nine standard sizes of mines, and they have added expensive safety appliances. These things have enlarged the requisite investment in plant and equipment by 1,000 per cent, in the last 20 years. ECONOMIES IN COAL WASHING.* By Sherwood Hua ter. Two of the most important economies in coal washing are :—(1) Economy in the actual washing of the coal; and (2) a proper lay-out, with the view of reducing to a minimum the cost of labour for handling and washing the coal. With regard to the first-mentioned economy, a guarantee is usually required for turning out a washed coal containing not more than 2 per cent, of free dirt and a resulting refuse with not more than 2 per cent, of free coal. Any plant that gives results within such guarantees can be considered economical, provided that there are no other losses during the washing process, namely, the settlings from the tanks through which the washing water is circulated or the sediment in the over- flow from such settling tanks. The general method of recovering the sediment (slurry) from the washing water is by means of an elevator, provided with perforated buckets, which dredges the slurry along with the whole of the washed fine coal from the pit; the coarser fine coal retains in the buckets a certain portion of the slurry. Owing to the amount of surplus water picked up by each bucket, ■slurry will not settle on the coal layer in the buckets, but is flushed through the draining holes in the bucket, and returns to the collecting pit, and in time the water thickens to such an extent that it becomes useless for washing. This thickened water, which must then be let off and replaced by fresh water,' and may contain up to 30 per cent, of sediment, is waste, because, even if it is led into separate tanks for drainage, the quality of the material is so poor that in most cases it does not pay for the labour entailed in recovering it. The recovery of slurry can also be effected by means of drainage bunkers. The whole of the fine coal, after washing, is swilled down troughs into one of a row of hoppers, the coal settling down and the water over- flowing into settling tanks, the sediment from which is pumped back into the hoppers. Perforated drainage pipes are placed inside the bunkers; these are fitted with taps at the bottom, which are closed whilst the hoppers are filling, and opened when the hoppers are full, thus allowing the water in the bunkers to drain away. This drainage water is pumped along with slurry from the settling tanks back into the coal trough that supplies further hoppers. This system has proved more satis- factory than the perforated bucket elevator, as the flush of the water in the overflow is not so strong, and allows a greater proportion of slurry to settle amongst the coal. Each drainage hopper is generally of a capacity of about 100 tons, and with a 100-ton-per-hour washery on an average, this would require about two hours to fill. Where the working of the plant is not continuous, or for some reason has to be stopped from time to time, a film of slurry accumulates on the top of the coal in the hoppers. This film prevents the drainage of any further coal filled in to such hoppers on top, so that it becomes necessary to change over into a new hopper each time that the plant has to be stopped, say, for want of coal, shortage of power supply, etc. A recent fine coal and slurry draining and mixing arrangement operates as follows :—The coal after wash- ing, arrives along with the . washing water in the distributor, and flows on to the drain sieves, where the bulk of the water and slurry is extracted, the coal being finally drained on vibrating sieves. The water along with the slurry is delivered into a settling tank; the slurry returns in a trough, and is concentrated on a sieve, and is finally drained on another set of vibrating sieves. The slurry, after passing over the sieve, is then mixed with the fine coal from the first-named vibrating sieves. The drainage from the concentrating sieves goes back into tile settling tank, wThereas the drainage from the ■shakers flows on to the fine coal, and passes along a vibrating screen, the coal acting as a filter and retaining the coal matter; the drainage, however, runs along a water shoot to the settling tank. In the case of this system, a current of water on the vibrating screens is practically non-existent, as the bulk of the water is drained off on the sieves, for which reason the slurry is retained. The greatest portion of the water is, of course, drawn from the drain sieve, where the fine coal arrives along with the water in which it has been washed. The coal, therefore, banks up on this drain sieve to a depth of 4 to 6 in.; a certain proportion of the slurry is retained in this layer of coal, and the mixture moves gradually down the incline on to the vibrating screens. The water with such slurry as passes through the sieve is delivered into settling tanks, from which the settlings are brought back on to the slurry sieves. The constructors of this appliance, which is called the “ British slurry refiner,” use a large conical settling tank in connection with their plants, into which the water collecting in the shoot is pumped, the slurry settling down and flowing by gravity on to the con- centrating sieve. The slurry has to be in a certain liquid state before it will flow through the pipes. This condition, however, owing to the large conical tanks, can be regulated to a nicety, for which reason the water proportion in the slurry is kept at a minimum. On arrival on the sieve, the excess water is immediately extracted, this water flowing back again to the pump and passing again through the settling tank; whereas the water which subsequently drains off the shakers is filtered on the drain sieve before it returns. With the combination of this slurry refiner and the elevated settling tank mentioned, it has been found possible to.work a washery, year in and year out, with- out any outlet whatever. The author then described the arrangement of a washery at a minimum cost for labour, handling, and washing. In the first place, the feed hopper is attached * From a paper read before the Manchester Geological and Mining Society. direct to the screening plant, the coal being delivered direct from the screens by means of a conveyor into the feed hopper, thus doing away with the loading at the screening plant and again unloading at the washery. If it should be desirable to wash coal coming in by railway, a small feed hopper is arranged alongside the above-mentioned feed hopper, and provided with auto- matic tipplers, the coal being elevated out of this small hopper into the1 other feed hopper. The coal is elevated into the washery by a feed elevator, where it is sub- jected to a double washing in a washer box, in the first part of which the heavy dirt, and in the second part the lighter dirt, is extracted. The washed coal flows along to the vibrating screens, where it is separated into fine- coal, singles, doubles, and trebles. The three last- mentioned are delivered into separate bunkers, from which they are loaded into railway wagons on separate railway sidings. The fine coal collects with the wash- ing water in the smudge sump, and after being elevated by the smudge elevator into the fine coal washer box, undergoes a third washing before it passes on to the fine coal draining arrangement and slurry refiner already mentioned. The water from the fine coal sieves collects in the pump sump, and is pumped by a centrifugal pump into a settling tank, where the slurry settles down, and is pressed by the gravity of the water on to a slurry refiner. The fine coal and slurry are then delivered direct into a loading bunker, from which the mixture is loaded into railway wagons. The dirt is elevated and drained in three separate dirt elevators attached to the washer boxes before it is delivered on to a scraper conveyor, which carries the dirt to a dirt bunker, and is then loaded into railway wagons. For the working of the whole of this washery of 125 tons per hour capacity, two men are sufficient, not count- ing, however, the men required for loading the washed products into railway wagons and for regulating the traffic under the washery. As no handling of the coal between the screening plant and washery is required, the cost of loading the wagons under the washery should be charged to the screening plant, because if there'were no washery, the wagons would have to be loaded at the screening plant. If the washery is separate from the screening plant, and the coal has to be loaded into rail- way wagons, the unloading and reloading at the washery would then become an additional charge to the cost of just the two men mentioned for running the washery. This minimum of labour is made possible by the fact that the whole of the washing is continuous, and all working parts are well within sight of one single man from any point of the plant. There are also no secon- dary settling tanks or water pits in connection with this plant, all points subject to wear and tear are get-at-able, and any necessary repairs are thus easily carried out. This type of plant ■ is suitable for ordinary colliery purposes where perfect drainage of thu fine coal is not essential, and where a moisture in the fine coal of 12 to 15 per cent, above the natural moisture in the coal is permissible. This moisture, however, would be too high for washeries, the slack from which is intended to go direct into coke ovens. Further, drainage for such can either be arranged for by means of a conveyor, which again makes the washery continuous, or by means of drainage bunkers, which latter system is not continuous. The washery is supplied wfith coal by means of the belt conveyor .into a feed hopper. A feed elevator delivers the coal into the washery, where it is subjected to’ the same treatment as described for the previous plant, with the exception that circular revolving screens are used for separating the coal into nuts, peas, and slack, instead of vibrating screens. The nuts and peas are swilled down troughs on to the drain tables; the drained nuts go into one bunker, and the peas .into another; both bunkers are provided with spiral shoots for the prevention of breakage. The drain water is returned to a pump sump. The washed fine coal, along with the washing water, arrives on the drain sieves, over which the drained fine coal passes into a draining conveyor. The, water and slurry from the drain sieves collect in the sump, whence it is pumped into a settling tank, in wl^ich the slurry settles down, and is brought back on to the slurry refiner, where it is drained before delivery into the draining conveyor on top of the fine coal. The coal from the sieves forms a layer in the bottom of the perforated compartment before the drained slurry is added on top. The mixture is thus graduated, and the remaining moisture quickly drains away all water collecting in the pump sump. The draining conveyor, which requires about three- quarters of an hour to complete the journey from one end to the other, delivers the contents to a disintegrator, the crushed coal falling on to a belt conveyor, and being conveyed into the coke oven service bunker. The fine coal and slurry sieves are in this instance proportionately shorter and of smaller area than described for the previous washery, where a good margin is essential to prevent any water from getting into the fine coal bunker. In the case of the draining conveyor, this is not necessary (and would also for structural reasons be rather difficult), as any excess moisture in the mixture that reaches the draining conveyor would drain away quickly through the perforations of the compartments. The washery next described is identically the same, with the addition only of drainage bunkers and crushers. The coal and slurry, after passing over the drain sieves, are delivered by means of a scraper conveyor into eight double sets of bunkers, each set holding 200 tons of fine coal, or a total draining capacity of 1,600 tons. Approxi- mately, 50 tons of fine coal per hour will be delivered into these bunkers, four hours being required to till each set of bunkers. As it has been assumed that the plant will work 16 hours per day, four sets of bunkers would be filled each