Environmental Engineering Reference
In-Depth Information
ozone production is mainly facilitated by plasma discharge. In this method, ozone
is generally generated through the passage of oxygen (or air) across the plasma
discharging zone. The fundamental principle in the ozone synthesis through
plasma discharge involves placing the oxygen-containing gas in a discharging
reactor, which is characterized by a low-temperature plasma atmosphere. Free
electrons at a certain energy level break oxygen molecules into oxygen atoms.
Ozone molecules are then produced through the three-body collision reaction,
while the ozone decomposition reaction occurs at the same time. Under the plasma
discharging conditions, ozone is generally believed to be obtained through the
following ways:
O
2
+e=O+O+e (2.10)
O+O
2
+M=O
3
+M (2.11)
O+O
3
=
2
O
2
(2.12)
e+O
3
=
O+
O
2
+e (2.13)
Two oxygen atoms are produced by using high-energy electron bombarding.
Oxygen atoms and oxygen molecules form O
3
through three-body collision
reaction, where M is a third-party gas molecule. Meanwhile, the O atom
accompanied with electrons may re-decompose O
3
. The ozone concentration at the
generator outlet is determined by a balance between the ozone generation and
destruction within the corona area. Various factors can affect the ozone yield, such
as the oxygen content in the feed gas, temperature, air purity, corona power
density, electrode cooling efficiency. For example, under same conditions, the
ozone output generated from pure oxygen is approximately two times of that from
air. Dust, oil, organic matters, and other impurities in the air source can affect the
electric current movement and adhere to the electrode surface, thereby influencing
the ozone production. Again, excessive vapor in the air source develops an arc
discharge to waste energy. Therefore, the air dew point is controlled at
temperatures ranging from 50 °C to 40 °C. Most of the power input within the
corona is dissipated in the form of heat, whereas a small part of the power input is
converted into light, sound, and chemical energies. Improving the frequency and
voltage of the power source is beneficial to the ozone production. However,
manufacturing the power source is difficult, and the dielectric parts of the power
source are easily broken
[5]
.
Nowadays, low-temperature plasma, which is obtained under room
temperature, is used to produce ozone. Different discharge types correspond to
different functions, including corona discharge, silent discharge, surface discharge,
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