Chemistry Reference
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odor control [61,62]. In addition to a stacked SD-DBD system, an SD-DBD with
structured electrodes mounted in the center of a pipe was used. In this system, the
pipe served as a casing and a flow path. The gas back pressure of this system is very
low. In the experiments conducted, the active areas of structured electrodes had an
extent up to 600 cm
2
.
In a typical operation mode, one of the electrodes formed the high-voltage elec-
trode and the second one was grounded. The plasma was produced in a small part of
the reactor, and the waste gas is mostly not in contact with the plasma part. Therefore,
this mode is predominantly applied for reactions by long living species like ozone. In
another control mode, the SD-DBD was sustained by sine wave pulse voltages. The
polarity was chosen as necessary. The grounded casing was situated in front of the
plasma electrodes. Positive or negative ions were extracted from the discharge side
by a potential difference. These ions penetrated the waste gas, making it a promising
treatment method.
The reactors and methods described earlier were used in different ways. In the
first method, the reduction of odors resulting from the production of French fries
was tested. The waste air cleaning system has different components and openings
for gas samples on different spots. At first, the waste air from a deep-fryer reaches
a high-efficiency particulate air filter made of foam material. This material works
as a sorption agent, and a prefiltration of water and oil aerosols is carried out there.
Due to this fact, systems like the plasma reactor or an activated carbon filter are
largely spared. The process diagnostics were done using UV-absorption spectroscopy
(ozone concentration), thermal desorption GC/MS (odor substances), FTIR (reaction
products), and olfactometry (odor). For smell analysis, we took gas samples of
approximately 8 l from the process gas during the preparation of French fries in
different places within a period of 2 min. For the determination of the basic level
of smells, further samples of the untreated and unloaded air were taken from the
surroundings.
For additional investigations, we introduced further plasma reactor configurations
than those described.
Figure 8.17 shows a comparison of the common SD-DBD configuration and the
pulsed SD-DBD with the odor strength of the raw gas. In the mode of sine wave
pulse voltages, there is near total odor reduction. Due to the grounded casing in front
of the plasma electrodes, positive or negative ions are extracted from the discharge
side. Thanks to this potential difference, the ions penetrate the waste gas. We assume
that the penetration of the waste air enables efficient decomposition of VOCs through
additional ion-molecule reactions. The experiments showed a correlation of odor
strength with odorous compounds such as VOCs. The VOCs were identified mainly
as aldehydes.
8.1.2.3 Concluding Remarks
Nonthermal plasma techniques offer an innovative approach for air pollution control.
There are various devices for nonequilibrium discharges and methods for pollution
control. Different reactor configurations were developed and tested for some arrange-
ments. The most important applications of nonthermal plasmas use corona discharge
