BRIQUETTES, a form of fuel artificially molded from coal dust and fragments, peat powder, lignite, etc., with the addition of some combustible binding material. The coal waste or slack is first washed and then dried in a rotating drum at a temperature ranging up to 500° F., until not more than 2 per cent of mois ture remains. It is then subjected to a blowing process which carries off most of the impurities — and in some cases considerable fine coal dust which is caught in baffle bins. The binder is added in proper proportion while the coal is hot, and the mass is mixed thoroughly by paddles and then sent into a heavy edge-runner mill where the constituents are ground into an intimate mixture. As it passes through this process it is kept hot by injections of live steam. The hot mixture is then passed to the molding rolls where it receives the desired shape at a pressure of from 3,500 to 5,000 pounds per square inch. The ((fins') remaining from inexact registering of the molding rollers are broken off by shaking on a revolving screen, and the briquettes are then allowed to cool and are ready for shipment.
Many substances have been used as binders, and most of them have been discarded for various reasons: they were too soft and melted down on the fire; or they made a heavy black smoke; or gave off an offensive smell; or burnt out too fast, leaving the coal unconsumed. The binders most commonly used by briquette manu facturers in the United States are coal-tar pitch, asphaltic pitch or a mixture of the two. A
comparatively new binder is the residuum of petroleum distillation known as hydrolene oil. This substance is solid up to 160° F., and only 5 per cent of the weight of the coal is needed to make the briquettes — as compared with 10 per cent in the case of pitch. These hydrolene briquettes give off very little smoke, which is quickly dissipated, and their heat value is higher than anthracite. They are particularly well suited to domestic use. In briquetting lignite, coal no binder is needed, the natural bitumen being developed by the process into a sufficient binder.
There were 15 briquetting plants in operation in the United States in 1916, with a combined output of 295,155 tons, valued at $1,445,662. Of the whole, 65,337 tons were of anthracite culm; 136,358 tons were of semi anthicite, semi-bituminous and bituminous slack; and 88,731 tons of lignite and oil-gas residuum. The quantity of binders added ac counts for the remainder of 4,929 tons. The production and use of briquetted fuel is much larger in Europe, the annual output being about 10,000,000 tons. Nearly the whole Eng lish product is exported. Consult Franke, G" (A Handbook of Briquetting' (London 1917). See FUEL.