Environmental Engineering Reference
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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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