And Utilization

AND UTILIZATION Lignite (see also Sections I. and II.) is the term commonly applied to immature coals, whether brown or black, or what American geologists term sub-bituminous coal. Properly speaking it comprises those solid fuels, young geologically, which have re tained their wooden structure, and have the appearance of decayed wood (Lat. lignis, wood). The greater mass of the brown coal deposits of Germany, for instance, though commonly spoken of as lignite, has not a woody structure, though it contains occasional deposits of true lignite. Brown coal is probably a land forma tion, as is shown by the considerable number of tree trunks con tained therein, and the deposits following naturally the cavities of the ground beneath the coal. Owing to the action of water and movements of glaciers, the deposits are sometimes interstratified with sand and clay.

Lignite is usually of Tertiary age. There is considerable varia tion in respect of its chemical composition, but two characteristics are fairly general, namely high moisture and volatile hydrocarbon content.

Prof. Elwood A. Moore gives the following as the composition of brown coal compiled from analyses of those coals derived from all parts of the world : As a matter of fact, the moisture content is higher in some instances than that given above.

The world's available supplies of lignite (brown coal or sub bituminous coal) were estimated by the Geological Congress held at Toronto in 1913 to amount to 2,997,763 million metric tons or about of the world's resources of fossil fuel. By continents the supplies were estimated to Million metric tons Europe 36,682 Asia III,851 Africa . . . . . . . . . I o54 America . . . .

2,81 I,906 Oceania 36,2 7o In the British Isles the deposits of brown coal are negligible; small deposits occur in Bovey Tracey in Devonshire and in County Antrim, Ireland. In Canada, Australia, New Zealand and India, the resources are, however, vast. In the United States of America there are also very extensive deposits of lignite.

The output of lignite and brown coal during the year 1924, as far as ascertainable, was i6r,oio,000 metric tons made up as follows : Metric tons Germany . . . . . . . . . . 124,360,000 Czechoslovakia . . . . . . . . . 20,507,000 Austria . Hungary . . . . . . . . . . 5,429,000 World's output, including small producers . . . 161,oio,000 The greatest producer of brown coal is Germany. It is custom ary in Germany to differentiate as between those deposits of brown coal which are rich in bitumen and those which have a low bitumen content. The "bituminous" brown coal deposits are usually from 2 5-65f t. thick, whereas the "lean" seams often attain to a thickness of 33o feet. The German industry is highly developed and flourishing. Many of the deposits are "stript," or worked "opencast"; that is to say, where not too deeply buried, the overlying deposits of sand, clay and gravel are removed by excavators. It is regarded as a profitable proposition to remove the "overburden" up to a thickness of three times the thickness of the underlying brown coal deposit.

The chief consumption of German brown coal is the electric power industry, and whereas in 1913 brown coal was the source of only 23% of the electric power generated, in 1922 it had risen to 41.2 %, the generation of electric power in Germany having more than trebled in that period, amounting in 1922 to 7, 200, 000,000 kw.-hours. With the concentration of electrical produc tion in large works built within the last ten years, a saving of from 15-2o% in coal has been effected.

The number of persons employed in producing the German output of 124,360,00o tons is about 134,14o. The uses to which the fuel is put besides being consumed in its raw state for domestic and industrial purposes are, (I) in conversion into briquettes, (2) the extraction of montan wax, (3) carbonization and recovery of the light oils, (4) recovery of paraffin for candle manufacture.

Briquetting.

As the coal in its raw state contains about 50 5 2 % of moisture it is first dried in steam heated driers down to 15% moisture, and then compressed by a steam actuated press, no binder being used, into briquettes of about Tin. long by 2 4in. wide and tin. deep with rounded ends. Formerly the use of brown coal briquettes was restricted almost entirely to domestic purposes, but latterly their use has extended to industrial and commercial undertakings. Generally speaking, the calorific value of the briquettes is double that of the raw brown coal. If the calorific value of German true coal (steinkohle) be taken in 7,000 calories, brown coal (braunkohle) at 2,500, and brown coal bri quettes at 5,00o calories, then one ton of German true coal is equivalent to about 2.8 tons of brown coal or 1.4 tons of brown coal briquettes.

In 1923, 52,254,00o metric tons of raw brown coal were con verted into briquettes by the dry process and 3,209, 00o by wet briquetting) in 239 works employing in all workmen.

Extraction of Montan Wax.

When brown coal is treated with naphtha or benzol, "bitumen" is obtained in the form of montan wax. The commercial process consists in treating the dried coal in extracting cylinders with a mixture of hot benzol and alco hol, the extracting arrangements operating in the same way as the well known Saxhlet extractors in chemical laboratories. The ben zol-alcohol is then evaporated and the montan wax recovered, the recondensed benzol and alcohol being used over again. It does not pay to extract the montan wax unless the raw coal is rich enough therein to yield io% of the substance on treatment in the labora tory by hot benzol.

There are not many deposits of brown coal in Germany suffi ciently rich in "bitumen" to allow of the extraction of that sub stance in the form of montan wax. This substance, which in its refined state has the appearance of bees-wax, is used in the manu facture of boot polish, cable wax, special greases, lacquers, elec trical insulation, gramophone records, light polishes, and as an addition to paraffin in the manufacture of candles. The price of raw montan wax averages £22 ios. per ton, the bleached wax fetching £87 ros.

The low temperature carbonization of lignite, and recovery of light oils and paraffin, is carried out in a retort known as the Rolle oven. It consists of a column of cast-iron circular collars super imposed one above the other, the column being enclosed in a fire brick erection. The coal passes down the narrow annular space between the column of collars and the enclosing firebrick cylin der which is heated by encircling flues, the gases distilled from the coal being drawn off through the collars and condensed in the or dinary way. The following figures are taken from actual results recently obtained at some carbonization works in western Germany : of coal containing 5o% moisture, 3-4 tons per 24 hours, per oven.

Semi-coke made per oven per day, r -1.5 tons or 33% of the raw coal. Tar (6o% of the possible yield as determined by analysis), 4-6% of the raw fuel.

Light oil stripped from the gas in proportion to tar, 16-2o%. Light oil per retort per day, 4.4 ib.

Consumption of brown coal for firing, 2%.

In the year 1923, 14,056,00o tons of raw brown coal were sub jected to distillation in 28 works employing in all 1,748 workers; 4, 5,00o tons of semi-coke were obtained and 7 76,00o metric tons of tar.