around the edges, where the fuel pile is thinnest. When burned on a
hearth the air for combustion is introduced into the furnace through
several rows of tuyeres placed above and symmetrically around the
hearth. An arrangement of such tuyeres over a grate, and a proper
manipulation of the ashpit doors, will overcome largely the objection to
grates and at the same time enable other fuel to be burned in the
furnace when necessary. This arrangement of grates and tuyeres is
probably the better from a commercially efficient standpoint. Where the
air is admitted through tuyeres over the grate or hearth line, it
impinges on the fuel pile as a whole and causes a uniform combustion.
Such tuyeres connect with an annular space in which, where a blast is
used, the air pressure is controlled by a blower.

All experience with this class of fuel indicates that the best results
are secured with high combustion rates. With a natural draft in the
furnace of, say, three-tenths inch of water, a combustion rate of from
250 to 300 pounds per square foot of grate surface per hour may be
obtained. With a blast of, say, five-tenths inch of water, this rate can
be increased to 450 pounds per square foot of grate surface per hour.
These rates apply to bagasse as fired containing approximately 50 per
cent of moisture. It would appear that the most economical results are
secured with a combustion rate of approximately 300 pounds per square
foot per hour which, as stated, may be obtained with natural draft.
Where a natural draft is available sufficient to give such a rate, it is
in general to be preferred to a blast.

Fig. 27 shows a typical bagasse furnace with which very satisfactory
results have been obtained. The design of this furnace may be altered to
suit the boilers to which it is connected. It may be changed slightly in
its proportions and in certain instances in its position relative to the
boiler. The furnace as shown is essentially a bagasse furnace and may be
modified somewhat to accommodate auxiliary fuel.

The fuel is ignited in a pit A on a hearth which is ordinarily
elliptical in shape. Air for combustion is admitted through the tuyeres
B connected to an annular space C through which the amount of air is
controlled. Above the pit the furnace widens out to form a combustion
space D which has a cylindrical or spherical roof with its top
ordinarily from 11 to 13 feet above the floor. The gases pass from this
space horizontally to a