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A change of plan has also been made in the gas
producer work. The earlier experiments were
conducted in producers such as are in use in commercial
plants, the tests at St. Louis and Norfolk
being in an up-draft producer, while the later tests
at Pittsburgh were in one of the down-draft type.
fn neither one of these installations could be carried
on some of the lines of investigation it was
desired to pursue, so the bureau has now established
at Pittsburgh an experimental equipment
of special design, in which certain problems are to
he studied. One of the latter relates to the possibility
and practicability of using in a gas producer
fuels of excessively high ash content. It is considered
that, in view of the many unsettled questions
in connection with gas producer design and
operation, a study of some of these in an experimental
installation will prove of greater value
than the continuance of tests of a more or less routine
nature in one of the commercial producers.
A similar conclusion has been reached regarding
the steaming investigation, and for this reason the
Bureau is no longer conducting the
COMMERCIAL BOILER TESTS
on various coals, as was done at St. Louis. This
statement is not be interpreted to mean that work
such as that done during the first few years is not
of value to the people of the country. There are,
however, factors which affect the results obtained
from the test of any one coal, and when there is
a wide variation in the coal to be tested, as there
is in the fuels from different sections of this
country, it is impossible to select any one type
of boiler and setting as installed in commercial
practice, and expect to get in this equipment the
best possible results from each coal. Such being
the case, it is readily seen that it will not beequally
fair to all fuels to test them in any one
equipment, if the results of these tests are to be
taken as an indication of the comparative value
of the coals for steaming purposes. Such trials.
it carefully conducted, would show very well the
values when used under certain conditions, bul
there is to-day little available information upon
which to base an opinion as to how much better
results for any one coal could be obtained byusing
a boiler and furnace of different design.
Of the factors affecting the evaporative results,
those dependent on furnace design and operation
may be separated from the factors governed by
boiler proportions, and are of greater moment
than the latter. For these reasons the bureau is
now making, in a specially constructed furnace and
combustion chamber, a study of some of the fundamental
principles of combustion and their relation
to furnace requirements.
It is now commonly known by engineers that to
completely burn a high-volatile coal at a given
rate of combustion, more combustion space is re­
THE COAL TRADE BULLETIN. 43
quired than to burn at the same rate a semibituminous
or semi-anthracite coal, assuming that
hoth fuels are stoked in the same way. There is,
however, no iniblished data as to what space is
required for any one of the typical coals, nor is
it known what losses occur if the space is less
than it should be. The study of this problem is
now being carried on by the Bureau of Mines and
constitutes the principal part of the steaming investigations.
For this work a special testing equipment has
been designed and built, consisting of a Murphy
mechanical stoker of 25 square foot grate area,
with the usual arch over the grates, to which is
joined a tunnel or combustion chamber about 35
feet long and with an internal cross-section approximately
3' 0" x 3' 0", and Heine water tube
boiler to absorb the heat generated. Provision
is made for taking gas samples, temperatures, and
other observations at intervals of five feet from
the bridge wall of the stoker throughout the length
of the tunnel. The latter discharges the products
of combustion into the combustion chamber proper
of the boiler setting, the gases then passing ovei
the heating surface of the boiler in the usual manner.
By taking simultaneous gas samples at a number
of places in the tunnel it is possible lo determine
not only how far the gases travel before the
coal is completely burned, but also what losses
would occur if the combustion was arrested at any
point. In this way data will be obtained as to
the furnace requirements for burning different
coals under various conditions. The
WORK NOW PLANKED
and being carried out includes tests with several
typical coals, in whicli tests the effect of the following
factors is to be studied:
(a) Nature of the coal.
(b) Rate of combustion.
( c) Supply of air.
(dl Rate at which the coal is heated.
(e) Rate ot mixing the volatile combustible and
air.
Another line of investigations related to the use
of fuel in boiler furnaces is the study of the
clinkering properties of ash, and of boiler feedwater
treatment. Tbe object of the work in clinker
formation is to determine the factors governing
this tendency and to devise, if possible, methods
for reducing the troubles from this source. It
is probable that when these investigations have
been continued a while, laboratory tests will be
developed, which, together with an analysis, wili
enable one to predict the clinkering action of an
ash under given conditions.
The boiler feed-water problem is being studied
along a line different from those followed heretofore,
in that experiments are to be conducted un-