Environmental Engineering Reference
In-Depth Information
3.3.3 Oxidation Mechanism Between O
3
and SO
2
SO
2
is usually high in flue gas but dissolves more difficult than SO
3
does. When
strengthening the reaction between O
3
and SO
2
,
the SO
2
absorption in a humid
washer increases, but unfortunately, SO
2
participates in reactions among NO, Hg,
and O
3
, thereby increasing the O
3
consumption. In light of WFGD dealing with
SO
2
efficiently, low energy consumption in a simultaneous multi-pollutants
removal process necessitates the lowest reaction degree between SO
2
and O
3
.
Experiments here focus on the oxidation reaction between O
3
and SO
2
under
conditions without catalysis, so as to understand the SO
2
oxidation mechanism
related with O
3
.
Experiments employed a tester similar to those in the previous oxidation
experiments. Additionally, the SO
2
concentration was measured by a PG250 gas
analyzer (Horiba) to avoid the interference of O
3
on the SO
2
absorption model.
NO
x
, SO
2
, CO, and CO
2
were measured by using the infrared absorption method.
The measuring range and precision of SO
2
were 500 and 1 ppm, respectively. The
molar ratio of O
3
to SO
2
was 1.0 and temperature ranged from 27 to 400 °C. The
original concentrations of SO
2
and O
3
were 34.8±5 and 1817±30 ppm, respectively.
Experimental results are shown in Fig. 3.13. It can be seen that the entire SO
2
oxidation efficiency is lower than 30% and effective oxidation temperatures are in
27 - 300 °C. The peak oxidation efficiency at 100 °C is 29.75%, whereas those at
temperatures exceeding 300 °C are almost zero. This is because that O
3
decomposes into O
2
at relatively high temperatures and no longer participates in
the reaction. Here the changing trend of the oxidation efficiency with temperature
levels is similar to that in the NO oxidation experiments.
At 100 °C, comparisons of NO concentrations with and without SO
2
existence
are shown in Fig. 3.14. At both two settings, the NO oxidation almost increases
linearly with the ratio of O
3
to NO. No obvious change appears in the NO
conversion rate when SO
2
is added, with the exception of slightly higher NO
conversion rates (after the ratio above 0.3) appearing at the setting without SO
2
.
The slight difference is attributed to the SO
2
oxidation that consumes parts of O
3
while develops only a small effect on the final NO oxidation. In conclusion, the
oxidation reaction rate between NO and O
3
is much higher than that of SO
2
and O
3
.
The presence of SO
2
has a small effect on the oxidation reaction between NO and
O
3
.
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