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Page 20
Per cent.
Carbonic acid, anhydrous 0.4
Sulphuric acid, anhydrous 0.26
Silica soluble 24.68
Silica insoluble 0.6
Alumina and oxide of iron 10.56
Lime 61.48
Magnesia, water, and alkalies 2.02
------
100
Again, fineness of the particles results in their being speedily
heated to a uniform temperature, so that they do not serve as nuclei
for the condensation of the moisture existing in the furnace gas. The
calcined material, on reaching the lower end of the furnace, is
discharged on to the floor or on to a suitable "conveyer," and removed
to a convenient locality for cooling and subsequent grinding or
finishing. It, however, is not in the condition of hard, heavy
clinkers, such as are produced in the ordinary cement kiln, which
require special machinery for breaking up into smaller pieces before
being admitted between the millstones for the final process of
grinding; nor does it consist of an overburnt exterior and an
underburnt core or center portion; but it issues from the cylindrical
furnace in a condition resembling in appearance coarse gunpowder, with
occasional agglutinations of small friable particles readily reduced
to fine powder in an ordinary mill, requiring but small power to work,
and producing but little wear and tear upon the millstones. The
operation is continuous. The revolver or furnace, once started, works
on night and day, receiving the adjusted quantity of powdered material
at the upper or feed end, and delivering its equivalent in properly
burnt cement at the opposite end, thus effecting a great saving of
time, and preventing the enormous waste of heat and serious injury to
the brickwork, etc., incidental to the cooling down, withdrawing the
charge, and reloading the ordinary kiln.
Cement, when taken from the furnace, weighed 110 lb. per bushel.
Cement, when ground, leaving 10 percent. on sieve with 2,500 holes to
the inch, weighed 121 lb. per bushel, and when cold 118 lb. per
bushel. When made into briquettes, the tensile breaking strain upon
the square inch:
At 4 days was 410 lb. per square inch.
At 6 days " 610 " " " "
At 14 days " 810 " " " "
At 49 days " 900 " " " "
At 76 days " 1,040 " " " "
A cylindrical furnace, such as the author has described, is capable of
turning out at least 20 tons of good cement per day of twenty-four
hours, with a consumption of about 3 tons of slack coal. It will be
readily understood that these furnaces can be worked more economically
in pairs than singly, as they can be so arranged that one producer may
furnish a sufficient quantity of gas for the supply of two cylinders,
and the same labor will suffice; but in order to provide for possible
contingencies the author advises that a spare gas producer and an
extra furnace should be in readiness, so that by a simple arrangement
of valves, etc., two cylinders may always be in operation, while from
any cause one may be undergoing temporary repairs, and by this means
any diminution in the output may be avoided.
The author considers it unnecessary here to discuss either the
advantages or the economy of fuel effected by the employment of gas
producers for such a purpose. These have been abundantly proved in
steel and glass making industries, where a saving of from 50 to 70 per
cent. of the fuel formerly employed has been made. Their cost is
small, they occupy little room, they can be placed at any reasonable
distance from the place where the gas is to be burnt; any laborer can
shovel the slack into them, and they do not require constant skilled
supervision. It is claimed by the author of this paper that the
following are among the many advantages derivable from the adoption of
this method of manufacturing Portland cement, as compared with the old
system:
(1) Economy of space--the furnaces, with their appurtenances,
requiring only about one-fourth the space of what would be
occupied by the ordinary kilns for producing the same quantity
of finished cement.
(2) Continuous working, and consequent economy of fuel lost by
cooling and subsequent reheating of the kiln walls.
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