494 _____________________________________________________________________________________________________________ THE COLLIERY GUARDIAN. September 6, 1918. of metallurgical coke must of necessity be a disad- vantage to the expansion and economy of the iron and steel trade of this country. There will be an increased foreign "demand for the best coking coals after the war, as some of the countries which produce relatively small quantities of iron and steel are making plans for increasing their output, and coke ovens will be included in their schemes. If they obtain the best coal, the home trade will have to use the more in- ferior qualities, which means a greater consumption of fuel. Even if it be found upon investigation that there is a suitable large reserve of coking coals in quantity sufficient to meet the needs of the increasing home iron and steel industry, every effort should be made to secure that any surplus available for export should, if destined to become metallurgical coke, be exported in that form, in order that the valuable by-products may be obtained in this country. From the summary of estimated quantities of gas production and consumption, it will be seen that such a plant as that suggested is theoretically self-supplying, but yet, as a stand-by, a mechanical gas producer plant, or surplus gas supplied by some neighbouring blast furnaces not producing steel, would be necessary for the continuous operation of the works. In any event, to take care of the unequal running of blast furnaces, and the loss of gas by leakage, an auxiliary supply of gas should be available, and this could be best obtained by connecting up various works in the same district. Linked Power Schemes. Further fuel economy could be effected if the various works of a large producing district could be linked together in their power schemes. Some of the works which only produce pig iron for the foundry trade, etc., would have a large surplus of gas, and this could be economically used in the other works which are making steel into various forms, and which would not have a surplus of their own unless they made more pig iron than they used in their steel furnaces. The linking up of all the coke ovens and blast furnaces in certain districts would result in there being made available, after meeting all the needs of the works, a surplus of hour units which, if converted into electricity, would be sufficient to provide a con- siderable amount of power for outside consumers. Assuming plants to be built on the lines indicated, the question naturally arises, what amount of fuel would be saved over the present system of making pig iron in one works, shipping it to another works in the cold condition, and this second works working it up as they do to-day? No correct estimate can be made as to what the actual saving would be, as to get at this very elaborate returns would have to be obtained from the entire iron and steel trade in its various branches. Although the calculations show that the coal car- bonised at the ovens can yield sufficient power for the operation of the works, yet for the sake of safety it is assumed that an extra 2 cwt. of fuel per ton of finished material is required; this added to the 33 cwt. of coal used in the coke ovens gives a total of 35 cwt. as being the total fuel required per ton of finished material. To compare this with present-day practice, we may take the case of a works which to-day is making standard articles, such as plates, sections, etc., from cold pig iron and scrap. Allowing that the blast fur- naces from which such a works obtains the pig iron in the cold state are only using the 23 cwt. of coke Note.—Calculations re the available gas from a works making 6,000 tons of finished steel per week. It is assumed that 6,000 tons of pig iron per week are required, and that the coke consumption is 6,900 tons per week, which is equivalent to 9,857 tons of coal weekly. Coke oven gas produced from 9,587 tons of coal per week (cu. ft.)____________... 98,750,000 Used in steel works at 8,000 cu. ft. per ton of ingots made (cu. ft.) (The heat value of the tar is not considered)______________ 60,000,000 Excess of coke -oven gas per week (cu. ft.) ____________________ Equal to an excess per hour of (cu. ft.) Which at 500 B.T.U. per cu. ft. equals (B.T.U. per hr.) ____________________ Part of which excess would be utilised in the soaking pits and reheating furnaces, leav- ing a surplus of (B.T.U. per hr.) ________ Blast furnace gas made from the production of 6,000 tons per week of pig iron at 150,000 cu. ft. of gas per ton of coke con- sumed per week (cu. ft.) Deduct 40 per cent, required for hot blast stove (cu. ft.) __________________________ Deduct the amount required for the manu- facture of coke in the coke ovens (cu. ft.)... Blast furnace gas available per week for power (cu. ft.) ________ ________ Amount available per hour (cu. ft.) ... At 100 B.T.U. per cu. ft. this equals per hour (B.T.U.) ___________________________ From the heating value of this blast furnace gas when converted into power in large gas engines the following amounts have been estimated in the paper to be required : For the supply of blast to the blast furnaces per hour (B.T.U.) ____________________ For the auxiliary plant on the blast furnaces and coke ovens (B.T.U.) For the auxiliary machinery on steel plant (B.T.U.) ___________________________ For power plant at rolling mill and repair plant (B.T.U.) ____________________ 38,570,000 229,500 114,750,000 30,750,000 1,035,000,000 414,000,000 621,000,000 246,425,000 374,575,000 2,229,600 222,960,000 71,775,000 16,086,000 8,000,000 145,000,000 Total hourly requirements (B.T.U.) ... 240,861,000 Total amount available per hour (B.T. U.) 222,960,000 Deficiency (B.T.U.) ______________ 17,901,000 The deficiency in heating value in the blast furnace gas is more than made up by the excess of coke oven gas. herein assumed to be necessary, then the saving in producing these standard materials in their condition as rolled, without any further working down, may be taken at 15 cwt. per ton of rolled material. Granting that 10,000,000 tons of such first stage products could be made in the future on the foregoing liue, then the saving in fuel would amount to some 7,500,000 tons per annum. Further fuel savings could be effected in working down these first stage products into more finished material provided economical power schemes were installed. It should be pointed out, however, that to accomplish the foregoing saving would mean practically the entire or partial scrapping of the greater number of the existing iron and steel works. Therefore the present capital involved would be largely lost, and much larger amounts of capital would be required in the erection of modern units on the lines indicated if the economical fuel results desired are to be obtained. _________________________ DETERMINATION OF INCOMBUSTIBLE MATTER IN MINE DUSTS.* By A. C. Fieldner, W. A. Selvig, and F. D. Osgood. In connection with the extension to various commer- cial mines of the bureau’s experiments on the use of rock dust for the prevention of dust explosions in coal mines, it has been desirable to use a rapid method for determining in mines the percentage of incom- bustible matter in the dust collected from roadways. For this purpose the Taffanel volumeter has been modified and combined with a compact, portable out- fit which can be easily transported to the mines. With this apparatus determinations can be made at the surface, or at convenient stations in the mine, to ascertain whether the desired proportion of rock dust has been added to the coal dust. Nature of the Incombustible Matter. The constituents of the dusts in coal mines may be classified as combustible and incombustible, as follows: (a) The combustible matter of the organic coal substance comprising various combinations of the elements carbon, hydrogen, oxygen, nitrogen, and a part of the sulphur; usually the greater part of the sulphur is to be considered as combustible, being present in the form of organic sulphur and iron pyrites (FeS2), which burns to ferric oxide (Fe2O3) and sulphur dioxide (S02); (5) incombustible matter con- sisting of clay, shale, slate and other silicates, silica in the form of sand and quartz grains, calcium sul- phate- in the form of gypsum, and calcium carbonate in the form of calcite; and (c) water or moisture. Method of Determination. In the usual methods of chemical analysis, the in- combustible is taken as the sum of moisture and ash in the material analysed. The percentage of com- bustible is then computed by subtracting the sum of the percentages of moisture and of ash from 100. The ash is determined by igniting a weighed amount of the sample placed in a porcelain crucible. The crucible is brought to a red heat in a muffle or over a burner, and heating is continued until no further loss in weight is sustained. The moisture is determined by drying a weighed amount of sample in an oven at a tempera- ture slightly above the boiling point of water (105 degs. Cent., or 221 degs. Fahr.). Strictly speaking, the percentage of incombustible in a coal-dust mixture is usually somewhat greater than that indicated by adding the percentages of ash and moisture. This discrepancy is due to the fact that certain incombustible constituents, such as combined water in the clay and shale, and carbon dioxide in carbonates, are expelled while the material is being ashed; that is, the ash weighs less than the incom- bustible constituents that it is taken to represent. Fortunately .this error is on the side of safety as regards mine dusts, as it makes the percentage of combustible matter appear slightly larger than it really is. Where incombustible is largely shale or clayey material, a correction factor of 1’5 may be applied to the ash to include the combined water, analysis of a number of shales that were considered for rock dusting having shown a combined water content of 4 to 6 per cent. In the analysis of dust mixtures of limestone and coal dust the loss of volatile incombustible matter in the form of carbon dioxide is so great that the sum of moisture and ash is considerably less than the true incombustible content of the mixture. The method for such mixtures is therefore modified in that the ash is determined by igniting the sample to constant weight at a temperature of 900 degs. Cent., so that all the carbon dioxide of the limestone is removed. The total percentage of carbon dioxide is then deter- mined in a separate sample, and this result is added to the percentages of ash and moisture. Expressed in formulas, the percentage of combustible matter is calculated as follows : — In mixtures of coal and shale : Combustible = 100 — (moisture +1-05 ash). In mixtures of coal and limestone: Combustible = 100 — (ash at 900 degs. Cent. 4- CO2 + moisture). Theory of Volumeter Method. The volumeter is simply a specific gravity flask with a graduated stem so proportioned that the volume of- a definite quantity of dust suspended in exactly 50 c.c. of alcohol can be measured by reading the meniscus of the alcohol on the graduated stem and referring to a calibration table. After the specific volume has thus been determined, or the specific gravity of the mixed dust, it is possible to calculate to within approxi- mately 5 per cent, the percentage of rock dust or ash in the mixture. This relation is due to the decided difference in the densities of coal and rock dust. The * From United States Bureau of Mines Technical Paper 144, real specific gravity of clean coal seldom varies beyond the limits 1-25 and 1-35. The average specific gravities of the various rocks and ash-forming impurities that are found in coal mines or used in rock dusting mines are: Clay, 1-9; soil, 2; shale, .2-6; slate, 2’8; lime- stone, 2-7; sandstone, 2-4; quartz, feldspar and calcite, 2-7; gypsum, 2-3; mica, 2-9; pyrites, 5. It will be noted that, with the exception of pyrites and some of the clays, the materials are practically twice as heavy as coal dust, and, furthermore, the numerical values are of the same order. Hence the ash or rock dust content of any mixture of these rocks with coal dust should be a linear function of the specific volume or specific gravity of the mixture. Bureau of Mines Volumeter. In using the Taffanel volumeter, it was found that the graduated measuring tube was too small to cover completely the ordinary range of densities encountered in road dusts and in rock dust mixtures; and in order to avoid this source of trouble, the dimensions of the volumeter were modified by increasing the capacity of the graduated part of the measuring tube from 5 c.c. to 10 c.c., the increased capacity being obtained by enlarging the diameter from 7 mm. to 8’6 mm., and lengthening the tube approximately 20 per cent. Detailed dimensions of the new volumeter and of the pipette, and the brass funnel used with it, are given in the illustration. The volumeter has a capacity of 57 ± 0T cc. to the lowest graduation (100) on the measuring tube. The graduated part of the measuring tube has a total volume of 10 0-05 c.c., and is graduated into 100 divisions. As the zero is at the top, the volumetric reading increases in direct ratio to the proportion of incombustible in the sample. A 20 gram sample will give a scale reading for all mixtures from 100 per Bureau of Mines Volumeter. -100 Etch E fi •6 I E E <=> E E c> E 40 s co od cent, coal to 100 per cent, rock dust. If the volumeter readings and the values for the ash or incombustible contents of a series of various mixtures of a given coal and rock dust are plotted as abscissas and ordi- nates respectively, the points will fall on a straight line, which is a calibration curve for all possible mixtures of the given coal and rock, or for any other coal and rock having the same specific gravity and the same moisture content; in fact, it is not necessary to pre- pare mixtures of the two constituents. As two points are sufficient to establish a straight line curve, it is necessary merely to make two volumeter determina- tions, one with 20 grams of the pure coal dust, and another with 20 grams of the pure rock dust. A straight line connecting the two points must pass through all points representing mixtures of the two constituents (assuming the same moisture content in all mixtures). Portable Outfit. The complete portable outfit for use at a mine for collecting samples of rqad and rib dusts and determin- ing the percentage of rock dust or dry incombustible is contained in a carrying case and weighs, including one quart of alcohol, approximately 20 lb. In the case cover are felt-lined recesses in which are fitted the glass parts of the outfit, pipettes, volumeter tubes and test tubes. The volumeter flasks are packed in felt- lined compartments contained in a tray 3 in. deep, which fits into the upper part of the box. This tray also contains the balance, weights, scoop, brush and other light articles. The heavier articles used in collecting the sample in the mine and the can of alcohol are packed in the space under the tray. On the top of the tray is fitted a thin board which prevents the articles in the tray from coming in contact with the glass parts in the cover during transportation, thus preventing breakage. This thin board also serves for a work table on which the balance is set up and the weighings are made. Making Volumeter Determinations. The outfit can be quickly prepared for making volu- meter determinations by opening the cover and re- moving the tray and its cover board and the other articles in the bottom of the box. The wire balance support is then removed from the cover board of the tray, and this board is inverted and placed back in the top of the box to serve as a weighing table.