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Furnace Design and the Combustion of Bagasse--With the advance in sugar
manufacture there came, as described, a decrease in the amount of
bagasse available for fuel. As the general efficiency of a plant of this
description is measured by the amount of auxiliary fuel required per ton
of cane, the relative importance of the furnace design for the burning
of this fuel is apparent.

In modern practice, under certain conditions of mill operation, and with
bagasse of certain physical properties, the bagasse available from the
cane ground will meet the total steam requirements of the plant as a
whole; such conditions prevail, as described, in Java. In the United
States, Cuba, Porto Rico and like countries, however, auxiliary fuel is
almost universally a necessity. The amount will vary, depending to a
great extent upon the proportion of fiber in the cane, which varies
widely with the locality and with the age at which it is cut, and to a
lesser extent upon the degree of purity of the manufactured sugar, the
use of the maceration water and the efficiency of the mill apparatus as
a whole.

[Illustration: Fig. 27. Babcock & Wilcox Boiler Set with Green Bagasse
Furnace]

Experience has shown that this fuel may be burned with the best results
in large quantities. A given amount of bagasse burned in one furnace
between two boilers will give better results than the same quantity
burned in a number of smaller furnaces. An objection has been raised
against such practice on the grounds that the necessity of shutting down
two boiler units when it is necessary for any reason to take off a
furnace, requires a larger combined boiler capacity to insure continuity
of service. As a matter of fact, several small furnaces will cost
considerably more than one large furnace, and the saving in original
furnace cost by such an installation, taken in conjunction with the
added efficiency of the larger furnace over the small, will probably
more than offset the cost of additional boiler units for spares.

The essential features in furnace design for this class of fuel are
ample combustion space and a length of gas travel sufficient to enable
the gases to be completely burned before the boiler heating surfaces are
encountered. Experience has shown that better results are secured where
the fuel is burned on a hearth rather than on grates, the objection to
the latter method being that the air for combustion enters largely