Briquette

Briquette is the name, originally French ('small brick'), given to a comparatively new form of fuel, made mostly from waste coal-dust, and used not merely for household purposes, but in various industries. A briquette is simply an admixture of coal-dust with pitch, moulded under pressure and heat, the pitch or some similar substance being introduced to form the cementing material. The size most generally adopted in Britain is about double that of the common building brick, and the weight about ten pounds. For household and domestic purposes, the smouldering qualities of the briquette give it especial value; it will remain alight for seven or eight hours, and can at any moment be roused by the poker into a cheerful flame. The heat given out is equal to that obtained from coal; and there is almost no smell in burning. Briquettes do not deteriorate by keeping. The coal-dust having been thoroughly cleaned by a stream of water from particles of clay, pyrites, shale, &c., is well dried in a cylindrical tube; it is then mixed with lumps of pitch in a disintegrator, which thoroughly combines the two ingredients, prior to their delivery into a vertical 'pug-mill.' Steam is now introduced into the pug-mill, rendering the pitch viscid and adhesive; the mixture, thoroughly amalgamated, then passes into moulds cut in a rotary die. Powerful rams, exerting a pressure of twenty pounds per square inch, force the material into each mould as it passes in rotation beneath. Nothing further remains but the delivery of each briquette after moulding on to a creeping band, where it is wet and cooled by a current of air from a fan, and delivered into a wagon below. Some kinds of baking coal will form briquettes without cementing material; and various substances have been used as cement—tar, asphalt, grease, spoilt flour and starch, waste from soap and other manufactures, gypsum, &c. On the Continent, brown coal is most frequently used, but there are briquettes of charcoal and coke also. France is the original home of briquette-making, which first attained commercial importance in 1832. France still manufactures briquettes on a larger scale than any other country. The use of hard pitch as cementing material is due to an Englishman, Wylam, in 1842. Briquettes have been approved of for heating the boilers of locomotives and marine engines, and in puddling and other furnaces, the chief hindrance in the way of their use being for a long time their cost. There are special works on the subject by Habets (Paris, 1870), Gurlt (Brunswick, 1880), Berg (Berlin, 1880), and Jünnemann (Vienna, 1881).