Practical Combustion Methods Used in Industries - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 239

Furnace temperature

200

Perheated air temperature

1500

160

120

1100 NOx concentration

80

Exhaust gas temperature

700

40

300 0

0 100 200 300 400 500 600

Time elapsed, s

FIGURE 4.19 Test data: preheated air temperature, exhaust gas temperature, and NO x con-
centration.

4.3.3 P OLLUTION R EDUCTION

The combustion phenomenon has been clarified through experiments using small-
scale laboratory combustion equipment on the combustion and the fluid flow, and
through flame image analysis.
When the combustion air reaches as high as 1273 K during combustion, if a
conventional burning method is used, a flame with an extremely high temperature
and luminosity is formed, and, therefore, the generation of NO x will increase quite
suddenly. However, even if the same high temperature air is used, if a low oxygen
content combustion (diluted combustion) by increasing the burned gas circulation
is realized, an entirely new high temperature air combustion will be realized with
characteristics of increased flame volume, lowered flame luminosity, and decreased
temperature gradient. At the same time a steady burning flame is formed in a large
space, and at that moment NO x generation is decreased rapidly.
The ultimate aim of our research is the commercialization of a furnace using
the clarified combustion phenomena described above, diluted and high temperature
air combustion in actual industrial furnaces. We have collected combustion and heat
transfer data using large industrial scale combustion laboratory equipment.
As a result, it has been verified that we can realize diluted slow burning in a
low oxygen content field even in a commercial furnace and can achieve a low
concentration of NO x generation even with high temperature air as high as 1273 K
by using the method of a nontile burner structure, high speed injection of combustion
air, and separate feeding of fuel and air, by promoting burned gas circulation, and
by suppressing the mixing of fuel and air simultaneously. To compare the structural
differences in the burners, the structure of the conventional burner and that of the
diluted and high temperature air combustion burner are shown in Figures 4.20 and
4.21 , respectively.