Environmental Engineering Reference
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3.4.1.4 Results and Discussion
The temperature distributions on the horizontal plane, including the central plane,
of injection ports of combustion air ( z = 1.5 m) and the slab are depicted in Figure
3.18 . This figure shows the main reaction regions are characterized by a high level
of temperature. The centers of two main reaction regions in Zone 1 have slightly
higher temperatures than the centers of the other two main reaction regions in Zone
2. This may be attributed to the fact that the fuel and combustion air input rates to
Zone 1 were higher than Zone 2. The combustion thus occurs at a higher rate, which
results in a higher temperature. On the other hand, the temperature outside the main
reaction regions in Zone 2 is slightly higher than that in Zone 1 as the slab temper-
ature is higher in Zone 2. Since the low-NO x burners used in this furnace limit the
mixing of the fuel with the combustion air in the initial stage, it can be seen, based
on the temperature distribution, that the primary reactions occur downstream from
the burners and long flames are produced. This results in a more uniform temperature
distribution, which corresponds to a lower NO x production rate.
The measured NO concentrations at the burner outlets in Zone 1, Zone 2, and
the auxiliary outlet were 66, 57, and 76 ppm (dry), respectively. However, the
magnitude of predicted NO concentrations was lower than the experimental data.
The lack of agreement between the predicted and measured NO concentrations may
be attributed to the deficiencies in the NO submodel, which cannot adequately predict
the governing flame structure at the current combustion temperature. In the gas-fired
1600
1400
1200
1000
800
600
400
FIGURE 3.18 Temperature distribution in the prototype furnace.
 
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