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Coal-washing experiments at seattle station
898
U.
S. BUREAU
OF MINES
NOTES.
[J. F. I.
thin enough to permit photography at a magnification of 2000 diameters. Much skill, experience, and patience are needed, however, to prepare them. The results of the first series of observations appear,ed in Bulletin 38 o’f the bureau, entitled : “ The Origin o’f Coal,” by David White and Reinhardt Thiessen, in 1914. The immediate cause that led the writer of this. article to investigate further the composition of coal and the origin and structure of its constituents was that when an attempt was made to discover the cause of the coking or nomn-coking properties of coal a more ,exact knowledge of the nature of coal was required. ilccordingly, samples were collected from representative bituminous coals in Pennsylvania, Indiana, Illinois, and Alablama, as well as various other localities in this country and in other countries. Results of this later study are pres’ented in Bulletin I I 7, recently in Paleozoic Bituminous issued by the bureau, entitled : “ Structure Coals,” by Reinhardt Thiessen.
COAL-WASHING
EXPERIMENTS
AT SEATTLE
STATION.
By Earl R. McMillan. COAL seams in the Northwest are rarely fre,e from “ bone ” and shale or clay partings, are nearly all folded and faulted, dip at In mining various angles, and in some cases are b’adly broken. seams the raw coal as it comes to the surface often contains as The Bureau of Mines much as 50 per cent. by weight of wa,ste. experiment station at Seattle is conducting washing tes’ts of this Since the process coal in order to improve it for commercial use. of coal-washing depends upon differences in specific gravity between the clean coal and its a.ssociated impurities, the first problem undertaken was that of d,etermining the specific gravity of the clean coal and of each parting of impurity contained in a large number of representative seams. It was found that the freshly mined coal is practically saturated with water, this being ob,served in samples varying from lowgrade subbituminous up to semianthracite, all of which are found The specific gravity values deterin the State of Washington. mined for the cleanest particles varied from 1.28 to 1.35; in general, the higher the rank of the coal the higher the specific gravity.
Dec., 192o.l
U.
S. BUREAU
OF MISES
KITES.
899
The raw coal contained a relatively small proportion of free prolportion being b’one, shale, particles of clean coal, the greater and clay particles, with specific gravities ranging from 1.35 to 2.65. The float-and-sink method was used to det,ermine the proportions of clean coal and of the heavier impurities, as well as the relations bletween their specific gravity and as’h content. As in use of this method of testing, difficulty arose in obtaining accurate and consistent results, it was necessary to standardize the method In the standardization tests it by a long series of careful tests. was found that the coal must be kept saturated with water throughout in order to obtain accurate (and comparablle) results. In order to, test large samples quickly and accurately, a float-andsink machine was built and, with experience, improved to a very satisfactory degree. The prime object of the tests is to devise washing methods that will prevent loss of good coal and easily and cheaply remove the dirt. In working out this prob!em, cooperative studies have been made lvith several of the coal-mining companies and gratifying results obtain,ed. For example, one company in the State of \Vashington for years has been discharging sludge into a pile i2s a result of washing tests recently estimated at 150,000tons. by the Cureau engineers, the mine owners are erecting a washing plant equipped with five tables for treating the entire pile. The material now has a recoverable value of $2 per ton, or a total of $225,000. At the plant of another coal company the raw nut coal contained ~3 per cent. ash. After washing in a jig, the leashed coal was found to contain 23 per cent. ash, and 15 per cent. of the feed lvas discharged as a washery refuse. After several days, experimenting with the ji g, using the float-and-sink test a.s a control, the ash in the was,hed coal was reduced to 16 per cent., with a recovery of 86 per cent. ; 92 per cent. of the wash,ed coal and 25 per cent. of the refuse floated on a I.55 solution, the loss of good coal in the refuse being reduced from 9.3 per cent. to 3.5 per cent. of the feed. Since approximately 250 tons a day are washed on this jig, the saving amounts to about 17 tons a day, which, at $1 per ton, is worth $68, also the services of two Fick,ers were dispensed with. effecting a further saving of $13.60 a day. The results are given in more detail in a recent report published by the blureau.
U.
S. BUREAU
OF MINES
NOTES.
[J. F. I.
thin enough to permit photography at a magnification of 2000 diameters. Much skill, experience, and patience are needed, however, to prepare them. The results of the first series of observations appear,ed in Bulletin 38 o’f the bureau, entitled : “ The Origin o’f Coal,” by David White and Reinhardt Thiessen, in 1914. The immediate cause that led the writer of this. article to investigate further the composition of coal and the origin and structure of its constituents was that when an attempt was made to discover the cause of the coking or nomn-coking properties of coal a more ,exact knowledge of the nature of coal was required. ilccordingly, samples were collected from representative bituminous coals in Pennsylvania, Indiana, Illinois, and Alablama, as well as various other localities in this country and in other countries. Results of this later study are pres’ented in Bulletin I I 7, recently in Paleozoic Bituminous issued by the bureau, entitled : “ Structure Coals,” by Reinhardt Thiessen.
COAL-WASHING
EXPERIMENTS
AT SEATTLE
STATION.
By Earl R. McMillan. COAL seams in the Northwest are rarely fre,e from “ bone ” and shale or clay partings, are nearly all folded and faulted, dip at In mining various angles, and in some cases are b’adly broken. seams the raw coal as it comes to the surface often contains as The Bureau of Mines much as 50 per cent. by weight of wa,ste. experiment station at Seattle is conducting washing tes’ts of this Since the process coal in order to improve it for commercial use. of coal-washing depends upon differences in specific gravity between the clean coal and its a.ssociated impurities, the first problem undertaken was that of d,etermining the specific gravity of the clean coal and of each parting of impurity contained in a large number of representative seams. It was found that the freshly mined coal is practically saturated with water, this being ob,served in samples varying from lowgrade subbituminous up to semianthracite, all of which are found The specific gravity values deterin the State of Washington. mined for the cleanest particles varied from 1.28 to 1.35; in general, the higher the rank of the coal the higher the specific gravity.
Dec., 192o.l
U.
S. BUREAU
OF MISES
KITES.
899
The raw coal contained a relatively small proportion of free prolportion being b’one, shale, particles of clean coal, the greater and clay particles, with specific gravities ranging from 1.35 to 2.65. The float-and-sink method was used to det,ermine the proportions of clean coal and of the heavier impurities, as well as the relations bletween their specific gravity and as’h content. As in use of this method of testing, difficulty arose in obtaining accurate and consistent results, it was necessary to standardize the method In the standardization tests it by a long series of careful tests. was found that the coal must be kept saturated with water throughout in order to obtain accurate (and comparablle) results. In order to, test large samples quickly and accurately, a float-andsink machine was built and, with experience, improved to a very satisfactory degree. The prime object of the tests is to devise washing methods that will prevent loss of good coal and easily and cheaply remove the dirt. In working out this prob!em, cooperative studies have been made lvith several of the coal-mining companies and gratifying results obtain,ed. For example, one company in the State of \Vashington for years has been discharging sludge into a pile i2s a result of washing tests recently estimated at 150,000tons. by the Cureau engineers, the mine owners are erecting a washing plant equipped with five tables for treating the entire pile. The material now has a recoverable value of $2 per ton, or a total of $225,000. At the plant of another coal company the raw nut coal contained ~3 per cent. ash. After washing in a jig, the leashed coal was found to contain 23 per cent. ash, and 15 per cent. of the feed lvas discharged as a washery refuse. After several days, experimenting with the ji g, using the float-and-sink test a.s a control, the ash in the was,hed coal was reduced to 16 per cent., with a recovery of 86 per cent. ; 92 per cent. of the wash,ed coal and 25 per cent. of the refuse floated on a I.55 solution, the loss of good coal in the refuse being reduced from 9.3 per cent. to 3.5 per cent. of the feed. Since approximately 250 tons a day are washed on this jig, the saving amounts to about 17 tons a day, which, at $1 per ton, is worth $68, also the services of two Fick,ers were dispensed with. effecting a further saving of $13.60 a day. The results are given in more detail in a recent report published by the blureau.