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Full text of "The Flow Of Gases In Furnaces"

APPENDIX IX

COMBUSTION AND BOILER SETTINGS
A. D. WILLIAMS
WHEN coal or other commercial solid combustibles are burned
directly in the firebox it is difficult and in some cases impossible
to obtain a temperature around 1600 C.; though the theoretical
combustion temperature of a good grade of coal in an athermal
enclosure is about 2050 C. This temperature limitation for a
long time hampered the development of many lines of metal-
lurgical and industrial work as the cost of obtaining the required
temperatures was too great for commercial use. The limitation
arises from the fact that it is practically impossible to force
sufficient air for complete combustion through the incandescent
bed of fuel; in other words, the bed of burning fuel acts as a
producer of combustible gases which in turn must be burned by
an additional air supply. The rate at which the air is forced
through the fuel bed directly affects the rate at which the fuel is
burned, but the mass of air per unit mass of combustible is prac-
tically constant under all conditions.
A very interesting series of tests on " Combustion in the Fuel
Bed of Hand-fired Furnaces " (Bureau of Mines, Tech. Paper 137)
has been made by Kreisinger, Ovitz and Augustine. One of the
features of this paper that attracted the writer's attention was the
statement that the mass of air per unit of combustible, computed
from the analysis of the gases in the upper layers of the fuel bed
was, in all cases, less than the mass of air per unit of combustible,
as measured by an orifice meter, introduced into the ash pit. The
quantity of air forced into the ash pit was also less than the
theoretical air supply required for the fuel.
In endeavoring to obtain an explanation of this difference it