be only large enough to carry a fire for igniting
the gas or for generating a small quantity of steam when the blast
furnace is shut down. The area of such grates has no direct bearing on
the size of the boiler. The grates may be placed directly under the gas
burners in a standard position or may be placed between two bridge walls
back of the gas furnace and fired from the side of the boiler. An
advantage is claimed for the standard grate position that it minimizes
the danger of explosion on the re-ignition of gas after a temporary
stoppage of the supply and also that a considerable amount of dirt, of
which there is a good deal with this class of fuel and which is
difficult to remove, deposits on the fire and is taken out when the
fires are cleaned. In any event, regardless of the location of the
grates, ample provision should be made for removing this dust, not only
from the furnace but from the setting as a whole.

Blast furnace gas burners are of two general types: Those in which the
air for combustion is admitted around the burner proper, and those in
which this air is admitted through the burner. Whatever the design of
burner, provision should be made for the regulation of both the air and
the gas supply independently. A gas opening of .8 square inch per rated
horse power will enable a boiler to develop its nominal rating with a
gas pressure in the main of about 2 inches. This pressure is ordinarily
from 6 to 8 inches and in this way openings of the above size will be
good for ordinary overloads. The air openings should be from .75 to .85
square inch per rated horse power. Good results are secured by inclining
the gas burners slightly downward toward the rear of the furnace. Where
the burners are introduced over coal fired grates, they should be set
high enough to give headroom for hand firing.

Ordinarily, individual stacks of 130 feet high with diameters as given
in Kent's table for corresponding horse power are large enough for this
class of work. Such a stack will give a draft sufficient to allow a
boiler to be operated at 175 per cent of its rated capacity, and beyond
this point the capacity will not increase proportionately with the
draft. When more than one boiler is connected with a stack, the draft
available at the damper should be equivalent to that which an individual
stack of 130 feet high would give. The draft from such a stack is
necessary to maintain a suction under all conditions throughout all
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