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Full text of "The Flow Of Gases In Furnaces"

DESIGN OF OPEN-HEARTH FURNACES               237
reason it would require designing talent of an extremely high order
and much serious study to produce a boiler which would not work.
Practically all of the boilers which have been built and installed
present extremely gross violations of some of the simplest and
most elementary laws of physics, not only in the circulation of the
heated gases but in the circulation of the water and steam. Owing
to their low ruling temperature these boilers work—that is, they
produce steam when hot gases pass through them, but their
utilization of the heat is comparatively inefficient when the
possibilities of such low-temperature applications are considered.
Some three years ago the writer, in the course of a discussion
before the Cleveland Engineering Society, stated that it seemed
to him that commercial boilers were much better designed for the
production of soot, a form of lampblack, than they were for the
production of steam. Since then he has seen no occasion to reverse
his opinion. At the same time he will admit that the low rate of
evaporation presents a certain margin of safety in boiler operation
—that is, the operating safety of a steam boiler depends upon the
maintenance of the supply of feed water. When the water supply
fails a very few minutes elapse before the water in the boiler
will be evaporated to a point where portions of the heating surface
will become dry. This is the danger point, and the higher the
rate of evaporation as compared with the volume of water con-
tained in the boiler, the quicker it will pass this danger line.
When the method of baffling steam boilers is examined, it will
be found that the hot gases are introduced at the lowest point of
the setting, that these gases rise in two of the passes and drop
through the middle pass, and are carried away from the highest
point of the setting. Experience with regenerators and similar
heat-absorbing structures has shown that this arrangement of gas
passages is absolutely illogical. Some waste-heat boilers without
baffling have been installed in connection with copper-smelting
furnaces, but in these installations the baffling was removed in
order to reduce the resistance to the passage of the gases through
the boiler, and the manner in which the gases were introduced and
carried away from the setting was not calculated to obtain the
best results. The main idea in the design appeared to be that
the gases should pass through the boiler setting as rapidly as
possible without any consideration of the utilization of their
sensible heat, while two boilers were placed in series in order to