578 THE COLLIERY GUARDIAN. March 23, 1917. COLLIERIES AND COKING PLANT AT THE DECAZEVILLE IRON WORKS.* By M. Leveque. The coal consumed at the Deeazeville Iron Works (Aveyron) is obtained from local deposits, one of which attains a thickness of 50 m., whilst for the most part their closeness to the surface enables opencast working to be carried on. The coal contains 35 to 36 per cent, of volatile matters, and about 12 per cent, of ash (when screened and washed, the small coke analysing .10-50 per cent.). The better grades of coal are sold, the more ashy kinds from the screening and washing plant being con- sumed in the works. In point of composition, Decaze- ville coal is. intermediate between the long-flame dry coals and the corresponding bituminous varieties, the analysis averaging (after deduction for ash and water) 80 per cent, of carbon, 5-70 per cent, of hydrogen, and 14-30 per cent, of oxygen and .nitrogen, the — X— H ratio being 2-51. The calorific power is low, being 7,650 ■■ Ordinary coke. • Coke with 10 per cent, anthracite. Fig. 1.—Decazeville Coke. calories, as compared with 8,000 to 8,500 calories for the general run of similar coals. The oxygen content is variable, attaining in one seam 15-96 per cent, without the coal having been oxidised. On the other hand, the coal possesses certain qualities which in practical use neutralise its apparent inferiority. It burns very readily, so that the boiler fires are easily stoked, there is little clinkering, and the grate is easily cleaned. When coked, Deeazeville coal furnishes a large quan- tity of gas of high illuminating value, for which reason it enjoys a high reputation among gas works. The mean composition of the gas is: Hydrogen, 50-32 per cent.: sulphuretted hydrogen, 0-49; methane, 34'28; carbon monoxide, 7’91; carbon dioxide, 2-60; oxygen, 1-48; and nitrogen, 2-03 per cent. The heating value, measured in the Junker calorimeter, is 5,400 calories per cu. m. The sulphur content of the coal is high, averaging 1-86 per cent. Part of this sulphur is in the condition of pyrites, the rest (0-91 per cent.) as sulphate. Owing to the oxidation of the pyrites, the coal had a tendency to overheat rapidly in some parts of the workings. Though the coal does not lend itself to the production of first-class coke, coking has been carried on ever since 1828; at first in heaps, like charcoal piles, and after- wards in Franqois ovens; but in 1875 a battery of Coppee ovens was erected, and in 1899 a battery of regenerative Otto by-product ovens. The yield of coke, at first 36 per cent., increased to 42 per cent., and then to 55 per cent, with the first Coppee ovens, being subsequently raised to 60 per cent.; whilst in the Otto ovens and stamped charges the present yield is 69 per cent. The coke from Deeazeville small coal is generally brittle and acicular. That from the Coppee ovens is porous, the apparent density being only 0-780, whereas the Otto coke is more compact, with a density of 0’900. On the other hand, the brittleness is considerably increased by stamping the charge. However, by mixing 10 per cent, of anthracite with the small coal, it has been found possible to lessen the brittleness and the tendency to break into acicular fragments, whilst retaining the increased density of the coke, with beneficial results to the metallurgical operations of the works. The coke now produced from the small coal with 10-50 per cent, of ash contains 15 to 16 per cent, of ash consti- tuents. It is somewhat high in sulphur, viz., 1'26 to 1-64 per cent., with an average of 1-50 per cent. The ash has the following composition : Silica, 51-40 per cent.; alumina, 22-74; lime, 3-70; magnesia, 1'99; ferric oxide, 15'01; phosphorus pentoxide, 0-66; sulphur, 0-82 per cent. The improved appearance of the coke is shown in fig. 1. Coal Winning. The total area of the coal concessions worked at Deeazeville amounts to 2,767 hectares (6,900 acres), and * Bulletin de la Societe de 1'Industrie Minerale. the annual extraction of coal to 670,000 tons. The bulk of the small coal is either coked or briquetted, 110,000 tons of the former, and 25,000 tons of the latter (blocks or ovoids) being produced per annum. The coal properties are divided into two groups— Deeazeville and Campagnac—which are under separate management. Of these, the Deeazeville group is the more important, producing over 500,000 tons per annum, as compared with 170,000 tons from the Campagnac workings. The coal deposits of the basin are split up into three groups of seams, separated by varying thicknesses of barret? measures. The Auzits_ seams belong to the lowest group, the Campagnac seams to the middle, and the Bourran seams to the top group. This last-named is the largest, and comprises a seam which in some places exceeds 50 m. in thickness. The seams of this group are usually near the surface, whereas those of the middle group dip, from the outcrop at Paley ret, where they are worked from the hillside, to a depth of 300 to 400 m. at Campagnac and Banel. At Deeazeville, most of the coal is won from the top group, and to a large extent in three open- cast workings. The Lasalle workings, which were begun in 1892, deal with the large Bourran seam, which forms two small basins or troughs, separated by a north- to - south anticlinal. Part of the smaller trough is worked by opencast, and yields one ton of coal for • every 3 cu.'m. of earth. The workings are in terraces, 4 m. broad, the coal being run down a self-acting incline to the screen- ing plant. The spoil is used partly for pack- ing the underground workings, the remain- der being tipped. The working progresses at the rate of about 14 m. per annum, for a pro- duction of 100,000 tons of coal. The total difference of level be- tween the top and bottom of the work- ings is about 120 m., 48 m. of which are coal. The Combes workings (fig. 2), which attack the Bourran seam on the'south, at the extremity of the larger trough, after being abandoned in 1865 in conse- quence of cavings, were resumed in 1908; and although the output is smaller than at Lasalle the workings are of a more imposing char- acter. The fire which succeeded the afore- said subsidence cal- cined or fused the schists in contact with the coal, causing them to turn a variety of colours from yellow to bright red, and from grey to deep violet. The working ter- races are 8 m. high and 6m. broad; and there are six of these in the coal and 10 in the rock, making the total height of the workings about 125 metres. A trial was made with steam navvies in 1912, two Ruston - Proctor machines being in- stalled in the upper terraces. Each bucket removes about 1 cu.m, of spoil at a stroke. The machines are served by two locomotives, which haul the spoil to the tips. Another opencast working, that at Tramont, is of minor importance, but is interesting on account of the undulating character of the seams. There are also open- cast workings at Firmy, but these were stopped in 1896 because they had approached the edge of the village, and the negotiations with the adjoining proprietors for the purchase of the house property could not be carried to a successful conclusion. The proportion of coal won at the Deeazeville open- cast workings is about one-fifth of the total tonnage, the rest being obtained from shafts. One of these shafts, which serves the workings of the Banel seam (part of Campagnac, or middle group), is 250 m. deep, and is e pped with a 350 horse-power winding engine. The moot, important deep mine is that in which the Bourran seam is worked, the coal being won in two lifts. The lower lift of very hard coal is worked by the longwall Fig. 2.—-Combes Opencast Workings. fit '’Arf. ■ ' : method, whilst the upper lift is taken out, the goaf being packed. The central (single) shaft, through which 400,000 tons per annum can be raised, is 100 m. in depth, but winding takes place, at present, from the 78 m. level only. The cages are of the two-deck type, each carrying three tubs, the total amount of coal raised per wind being 2'4 metric tons. The winding engine is of 250 horse- power. Pumping.—The pumping plant is centralised at this shaft, and consists of two electrically-operated Jandin pumps, capable of raising 1,056,000 gals, per 24 hours, there being also, as an auxiliary, a Sulzer centrifugal pump, with a capacity of 33,000 gals, per hour. The old pump at Combes, which was installed in 1880, and can- raise over 1,000,000 gals, a day, is still available as a stand-by. This extensive plant is necessary, in view of the danger of the workings being flooded from the surface by violent storms, and of the fact that the natural influx of water sometimes exceeds 1| million gals, per diem. The central shaft is connected with the screening plant and the Lassalle workings by self-acting inclines, the tubs being elevated at the screens and run back by chain haulage. In the case of thick seams near the surface, as is the case at Deeazeville, the only difficulty to be surmounted in working is the risk of fire. Without going into details of the precautions adopted to fight possible fires, it may be mentioned that two hydraulic stowage plants have been installed, at Bourran and Combes, which will greatly assist working operations through the greater compactness of the stowage. Screening and Washing Plant.—All the coals from the various workings are forwarded to the screening plant near the central shaft. Here there are installed five screens, each capable of dealing with 400 tons of coal in 10 hours. All the smalls (below 60 mm.) from the screens are taken to the washery by two belt conveyors. The washing plant comprises six Commentry washers, .with a capacity of 1,000 tons of coal in 24 hours, pro- ducing three grades of coal for safe : ‘ ‘ Petits greles, ’ ’ nuts, and small; and two (“ greles barres ” and “ barres ”) which are consumed at the mines and in the works. The coal from the Campagnac workings is put through -i screening plant dealing with 150 tons per houf. The large coal is hand-picked on two belts, and the grades below 60 mm. are sent to a washery (capacity 120 tons an hour), comprising six ordinary piston washers for the larger sizes and 16 felspar washers for the smalls. The “ barres ” are utilised for steam raising on the premises. Compressed Air Plant.—The compressed air for work- ing the mines is generated at Deeazeville by a com- pressor at Lacaze, driveq by a 350 horse-power Collmann engine, the compressor drawing in 60 cu.m, of air per minute, which it delivers under a pressure of 85 1b. per sq. in. At the Campagnac mines there are two com- pressors, one of 150 horse-power dealing with 40 cu.m, of air, and one of 250 horse-power drawing in 55 eu. m. of air per minute, the delivery pressure in both cases being 71 lb. per sq. in. Boilers.—The steam for operating the winding engine at the central shaft and the Lacaze compressor engine is generated in a battery of Babcock boilers, heated by low- grade coal, such as washery sludge, “ barres,” etc. The battery comprises 12 boilers, with a heating surface of 220 sq. m.; and six of them are equipped with Babcock and Wilcox mechanical .stokers. The ashes are removed by a current of water in the ashpit, which delivers them to a sump served by two elevators, one of which returns the water to the flushing tank, whilst the other dis- charges the ashes into a hopper, whence they are con- veyed by trucks to the dump. Electric Power Station.—The same battery of boilers also supplies the steam for the electric power house at Lacaze, which furnishes current to the mine and works. The power house is equipped with plant for generating direct current at 280 to 300 volts, and triphase current at 3,300 volts. The direct current is generated by two compound tandem Collmann engines, running at 110