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Full text of "The Flow Of Gases In Furnaces"

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118

RATIONAL CONSTRUCTION OF  FURNACES

the flow of the gases in the lower part of the setting by the use
of an open checker.
By this artificial means it is possible to pass the greatest
portion of the hot gases near the bottom of the setting and in this
manner the temperatures £max and W may be very nearly equalized.
Therefore, in the portion C of the tunnel chamber the checkerwork
of the ware set to burn should be set close at the top and open at
the bottom.
The portion A of the tunnel chamber will be considered next.
This portion is filled with hot ware cooling, and through it is
passed the current of cold air to be heated. This air is a cold
and heavy fluid which will flow in the lower portion of the setting
without any tendency to rise. The only way in which this stream
of air can be forced to flow in the upper portion of the tunnel
chamber is to increase the resistance to its flow by the checker
work built in setting the ware in the tunnel, which for this purpose
should be set close at the bottom and open at the top, where less
resistance is required. Upon comparing the conditions required
in section A with those required in section C of the tunnel chamber,
it will be noted that they are diametrically opposed to each other.
It is true that the contraction of the brick or lime, in burning,
favors the correct method of operation in these sections. Since,
in the section of the tunnel chamber A, an open space will be
formed below the roof of the tunnel, due to the skrinkage of the
charge, this open space will be quite large in those kilns used in
burning lime. But in general, the operation of ring tunnel kilns
presents a complicated problem, to which there are two possible
compromise solutions:
1.  One solution secures an even heating of the crude material,
but the incoming air is poorly preheated and the cooling ware is
subjected to a sharp drop in temperature which is very liable to
result in cracked and spawled ware;
2.  The other solution secures a uniform preheat of the incoming
air and results in the gradual cooling of the burned ware, but
at the same time results in a non-uniform heating of the unburned
ware.
The first of these methods of operation is the one ordinarily
employed. For example, at the Wachter works at Borovitch, a
kiln of this type is used for burning firebrick. The lower part of
the tunnel is charged with lumps of fire clay whose quality will not