Environmental Engineering Reference
In-Depth Information
NO+O
3
=
NO
2
+O
2
(3.14)
NO
2
+O
3
=
NO
3
+O
2
(3.15)
NO
2
+NO
3
=
N
2
O
5
(3.16)
NO+O+M
NO
2
+M (3.17)
NO
2
+O
=
NO
3
(3.18)
Among the five reactions, NO
2
is the main product when the O
3
/NO
stoichiometric ratio is smaller than 1.0 and this property has been confirmed by
experimental results here. Results at temperatures ranging from 373 to 673 K are
shown in Fig. 3.10. For the interference of NO
2
, the ozone and NO
2
concentration
detection module (UV) of CEMs is inaccurate and can only be considered as a
nitrogen tracer. The oxidation products with respect to the O
3
/NO stoichiometric
ratio at 473 K are shown in Fig. 3.11. N
2
O, NO
3
, and N
2
O
5
are minority products
[4]
to be measured difficultly. Therefore, only NO of NO
x
is trusted in the present
experiment. The NO in the original simulated flue gas was diluted with N
2
. On the
basis of observations in Fig. 3.10, NO can be effectively oxidized by ozone, but
the result varies with temperature. The two lines of 373 and 473 K almost overlap,
and nearly 85% of NO can be oxidized when 200 ppm ozone is added with a
stoichiometric ratio of approximately 0.97. The oxidation rate increases almost
linearly with the ozone level. Considering that ozone is a type of unstable gas that
automatically decomposes into O
2
particularly at high temperature levels, Fig.
3.12 depicts the thermal decomposition property of the ozone-enriched gas.
Experiments were conducted in a multi-sample glass tube with an oil bath for heat
supplying. The initial ozone concentration was 4400±250 ppm. The temperature
ranged from 298 to 523 K and residence time was 0.2 - 10 s. At room temperature
(298 K), only 0.5% of ozone disappeared within 10 s. The decomposition rate
dramatically increased with the temperature, particularly when the temperature
reached 473 K. At 523 K, more than 80% of ozone decomposed within 1 s. At the
same time, the residence time in the reactor decreased from 0.089 to 0.049 s when
the temperature increased from 373 to 673 K. The two reasons thus decreased the
NO conversion at 573 K.
Moreover, Fig. 3.10 shows that only 52.5% of NO can be oxidized at 573 K
when 192 ppm ozone is in an atmosphere with the aforementioned stoichiometric
ratio of approximately 0.89. At 673 K, almost no NO oxidation could achieve
because of a strong ozone decomposition. Thus, in the future industrial application,
=
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