The briquettes made at this plant are then subjected to physical tests in order to determine their weathering qualities and their resistance to abrasion; extraction tests and chemical analyses are also made. Meanwhile other briquettes from the same lots are subjected to combustion tests for comparison with the same coal not briquetted. These tests are made in stationary boilers, in house-heating boilers, on locomotives, naval vessels, etc., and the results, both of the processes of manufacture, and of the tests, are published in various bulletins issued by the Geological Survey.[27]
The equipment includes storage bins for the raw coal, scales for weighing, machines for crushing or cracking the pitch, grinders, crushers, and disintegrators for reducing the coal to the desired fineness, heating and mixing apparatus, presses and moulds for forming the briquettes, a Schulz drier, and a cooling apparatus.
There is a small experimental hand-briquetting press (Fig. 1, Plate XXI) for making preliminary tests of the briquetting qualities of the various coals and lignites. With this it is easily possible to vary the pressure, heat, percentage and kind of binder, so as to determine the best briquetting conditions for each fuel before subjecting it to large-scale commercial tests in the big briquetting machines.
This hand press will exert pressures up to 50 tons or 100,000 lb. per sq. in., on a plunger 3 in. in diameter. This plunger enters a mould, which can be heated by a steam jacket supplied with ordinary saturated steam at a pressure of 125 lb., and compresses the fuel into a briquette, 8 in. long, under the conditions of temperature and pressure desired.
The Johnson briquetting machine, which requires 25 h.p. for its operation, exerts a pressure of about 2,500 lb. per sq. in., and makes briquettes of rectangular form, 6¾ by 4¼ by 2½ in., and having an average weight of about 3¾ lb. The capacity of the machine (Fig. 2, Plate XXI) is about 3.8 tons of briquettes per 8-hour day.
Under the hopper on the scales for the raw material is a square wooden reciprocal plunger which pushes the fuel into a hole in the floor at a uniform rate. The pitch is added as uniformly as possible by hand, as the coal passes this hole. Under this hole a horizontal screw conveyor carries the fuel and pitch to the disintegrator, in front of which, in the feeding chute, there is a powerful magnet for picking out any pieces of iron which might enter the machine and cause trouble.