Environmental Engineering Reference
In-Depth Information
1.0
over
temperature
zone
0.8
0.6
0.4
blow off
zone
0.2
heat
exchanger
limit
0.0
FIGURE 2.34
Thermal efficiency affected by gas recirculation and the maximum combustion
gas temperature.
2.2.4.5
Summary
1. An improved heating method combining high temperature additional
enthalpy combustion with gas recirculation was demonstrated, making it
possible to have a uniform temperature profile in furnaces and to increase
the average temperature.
2. A one-dimensional plug-flow type of furnace model was studied and the
level of the heat loss from recirculating gas was proved to strongly affect
the gas temperature in the furnace.
3. The operation increasing both gas recirculation ratio and heat recirculation
can result in the reduction of both the maximum temperature and temper-
ature gradients in the furnace. It can be expected this could, in principle,
bring about NO
x
reduction.
4. Thermal efficiency was improved by the operation of increasing gas
recirculation and heat recirculation while maintaining a constant maxi-
mum flame temperature. It was found that an optimum point exists in
terms of satisfying thermal efficiency improvement and NO
x
abatement.
2.3
FUNDAMENTALS OF GASEOUS FUEL FLAMES
2.3.1
E
XTINCTION
L
IMIT
AND
N
O
X
IN
L
AMINAR
D
IFFUSION
F
LAME
It was commonly believed that a diffusion flame in a high temperature airflow generates
a larger amount of NO
x
than in room temperature air because of the higher flame
temperature. For this reason, NO
x
reduction has been pursued by lowering both the
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