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RATIONAL CONSTRUCTION OF FURNACES
V. IRON TUBE HOT-BLAST OR AIR HEATERS
This type of apparatus is now practically unknown, except
for the description of it which may be found in various books.
In the Manual of Metallurgy, by Percy-Wedding, twelve types
of iron tube air heaters are described, some dozen or so of pages
being devoted to their construction and the causes which led to
their being abandoned. Of the many types of this apparatus, the
only ones which have survived are those of the Besseges works
and the Cleveland type; all of the others have passed out of use.
The reason for their abandonment is very simple: all of the
iron tube air heaters described by Percy-Wedding had the outlet
for the waste gases at their highest point. The hottest gases of
combustion rose immediately to the top of the chamber, licking
the surface of the iron tubes, and heating them irregularly, the
top being much hotter than the bottom. The tubes, heated in
this manner, burned out, warped and broke.
In the Besseges type of air heater the products of combustion
pass from chamber to chamber through ports in the division walls.
These ports are located at the level of the hearth. In this appa-
ratus the reacting portion of the flaming gases rise and then drop
through zones of uniform heating, where combustion is completed.