Practical Combustion Methods Used in Industries - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 230

70
60
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40
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20
Type of recuperator
FIGURE 4.12 Types of recuperator and its heat recovery rate.
higher than 1250˚C. The value of 100 ppm NO x can be passed without problems at
a preheated air temperature well over 1000˚C and at a furnace temperature higher
than 1300˚C.
The change of driving mechanism from a pusher-type furnace to a walking-
beam-type began in 1967. Recently, a multiple-zone-type walking beam furnace has
become predominant. Technical measures to counter skid marks have not been solved
yet. Various counter-measures have been worked out, such as shifting of the skid
beam, heating method for aiming at the skid contacting portions by burners with a
long head that project out from the noses standing up through the furnace hearth
and from the furnace sidewall, adoption of gate-type posts, adoption of a taller skid-
height, and moderate cooling of skids. However, no effective countermeasure has
been found to date.
The applied HiTAC burner uses technologies of blowing air at a high velocity
to achieve homogeneous combustion entirely inside the furnace. Therefore, it is
expected that the gas, which was stagnating in all methods so far, will be able to
flow to the surroundings of the skid supports to where the gas did not diffuse. By
this effect, it is also expected that homogeneity of ambient atmospheric temperatures
in the lower part of the furnace can be improved, resulting in a decrease of skid marks.