Principle of Multi-Pollutants Removal Technology in Flue Gas by Ozone - Simultaneous Multi-Pollutants Removal in Flue Gas by Ozone - page 38

2.3.3 Dielectric Material
The dielectric, which is an important part of a silent electrical discharge system
(i.e., the dielectric barrier discharge) equipped in an ozone generator, is used to
strengthen the electric-field intensity in air gap for a more successful discharge. In
addition, the dielectric prevents the air gap from breakdown, reduces power
consumption, develops a uniform electric field in the air gap, and expands the
discharge area, thereby facilitating the ozone generation. Generally, a higher
dielectric constant corresponds to a better thermal conductivity and thus promotes
the ozone production.
Currently, the dielectric in an ozone generator can be made by quartz glass,
ceramic, enamel, and various types of organic materials. These materials are
described below.
1) Ceramic and enamel
Highly pure alumina ceramics are characterized by a high melting point,
mechanical strength, breakdown voltage, resistance to chemical corrosion, and
thermal conductivity. In recent years, the material and processing technique
applied in dielectric layers have become the key technologies in forming a
strongly-ionized dielectric barrier discharge field. Through the plasma spraying or
other methods, an ultrathin and dense -Al 2 O 3 dielectric layer is formed in the
surface (with an area of 400 - 1600 cm 2 ) of both the discharge and grounding
electrodes. Consequently, various advantages such as high strength, high density,
high insulation, high dielectric constant, high uniformity, low curvature correction,
and low loss appear in this type of dielectric layers [29-31] .
Aside from theirs high electric strength, large dielectric constant, and strong
corrosion resistance, ceramics also have a simple manufacturing process [32] .
2) Bi-dielectric composite materials
In this aspect, only the mica application is selected as the example. Zhao et
al . [33] used a ferroelectric/dielectric gap structure comprising a pair of plate
electrodes and dual dielectric layers. A 0.1-mm-thick mica layer was positioned on
the lower electrode. Meanwhile, a 1-mm-thick teflon layer with several
centrally-located 10-mm-i.d. holes (used to position 1-mm-i.d. - 3-mm-i.d.
ferroelectric spheres), was located on the mica layer. This mica and teflon
bi-dielectric configuration can extend the ozone generator duration under
high-humidity conditions.