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Figures represent nominal rated horse power. Sizes as given good for 50
per cent overloads.

Based on centrally located stacks, short direct flues and ordinary
operating efficiencies.

Table 56 gives the sizes of stacks, and horse power which they will
serve for oil fuel. This table is, in modified form, one calculated by
Mr. C. R. Weymouth after an exhaustive study of data pertaining to the
subject, and will ordinarily give satisfactory results.

Stacks for Blast Furnace Gas Work--For boilers burning blast furnace
gas, as in the case of oil-fired boilers, stack sizes as suited for coal
firing will have to be modified. The diameter of stacks for this work
should be approximately the same as for coal-fired boilers. The volume
of gases would be slightly greater than from a coal fire and would
decrease the draft with a given stack, but such a decrease due to volume
is about offset by an increase due to somewhat higher temperatures in
the case of the blast furnace gases.

Records show that with this class of fuel 175 per cent of the rated
capacity of a boiler can be developed with a draft at the boiler damper
of from 0.75 inch to 1.0 inch, and it is well to limit the height of
stacks to one which will give this draft as a maximum. A stack of proper
diameter, 130 feet high above the ground, will produce such a draft and
this height should ordinarily not be exceeded. Until recently the
question of economy in boilers fired with blast furnace gas has not been
considered, but, aside from the economical standpoint, excessive draft
should be guarded against in order to lower the upkeep cost.

Stacks should be made of sufficient height to produce a draft that will
develop the maximum capacity required, and this draft decreased
proportionately for loads under the maximum by damper regulation. The
amount of gas fed to a boiler for any given rating is a fixed quantity
and if a draft in excess of that required for that particular rate of
operation is supplied, economy is decreased and the wear and tear on the
setting is materially increased. Excess air which is drawn in, either
through or around the gas burners by an excessive draft, will decrease
economy, as in any other class of work. Again, as in oil-fired practice,
it is essential on the other hand that a suction be maintained within
all parts of the setting, in this case not only to provide agai