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.
The ground mixture is elevated from the disintegrator to a point above
the top of the upper mixer of the machine. At the base of this cylinder,
steam can be admitted by several openings to heat the material to any
desired temperature, usually from 180° to 205° Fahr. There, a plunger,
making 17 strokes per min., compresses two briquettes at each stroke.
The German lignite-briquetting machine (Figs. 18 and 19) was made by the
Maschinenfabrik Buckau Actien-Gesellschaft, Magdeburg, Germany. Lignite
from the storage room on the third floor of the building is fed into one
end of a Schulz tubular drier (Fig. 1, Plate XXII), which is similar to
a multi-tubular boiler set at a slight angle from the horizontal, and
slowly revolved by worm and wheel gearing, the lignite passing through
the tubes and the steam being within the boiler. From this drier the
lignite passes through a sorting sieve and crushing rolls to a cooling
apparatus, which consists of four horizontal circular plates, about 13
ft. in diameter, over which the dried material is moved by rakes. After
cooling, the material is carried by a long, worm conveyor to a large
hopper over the briquette press, and by a feeding box to the press (Fig.
2, Plate XXII).
The press, which is of the open-mould type, consists of a ram and die
plates, the latter being set so as to make a tube which gradually tapers
toward the delivery end of the machine. The briquettes have a
cross-section similar to an ellipse with the ends slightly cut off; they
are about 1¼ in. thick and average about 1 lb. in weight (Fig. 2, Plate
XX). The press is operated by a direct connection with a steam engine of
150 h.p., the base of which is continuous with that of the press. The
exhaust steam from the engine is used to heat the driver.
The plunger makes from 80 to 100 strokes per min., the pressure exerted
ranging from 14,000 to 28,000 lb. per sq. in., the capacity of the
machine being 1 briquette per stroke, or from 2½ to 3 tons of completed
briquettes per hour. It is expected that no binder will be needed for
practically all the brown lignite briquetted by this machine, thus
reducing the cost as compared with the briquetting of coals, which
require from 5 to 7% of water-gas, pitch binder costing more than 50
cents per ton of manufactured briquettes.
[Illustration: Fig. 18.