Odor removal characteristics of a laminated film-electrode packed-bed nonthermal plasma reactor.

Abstract

Odor control has gained importance for ensuring a comfortable living environment. In this paper, the authors report the experimental results of a study on the detailed characteristics of a laminated film-electrode and a laminated film-electrode packed-bed nonthermal plasma reactor, which are types of dielectric barrier discharge (DBD) reactor used for odor control. These plasma reactors can be potentially used for the decomposition of volatile organic compounds (VOCs) and reduction of NO(x). The reactor is driven by a low-cost 60-Hz neon transformer. Removal efficiencies under various experimental conditions are studied. The complete decomposition of the main odor component, namely, NH(3), is achieved in a dry environment. The retention times are investigated for the complete removal of NH(3) in the case of the film-electrode plasma reactor and the film-electrode packed-bed plasma reactor. The removal efficiency of the former reactor is lower than that of the latter reactor. Mixing another odor component such as CH(3)CHO in the gas stream has no significant effect on NH(3) removal efficiency.

Full text

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Sensors 2011, 11, 5529-5542; doi:10.3390/s110605529

sensors
ISSN 1424-8220
www.mdpi.com/journal/sensors
Article
Odor Removal Characteristics of a Laminated Film-Electrode
Packed-Bed Nonthermal Plasma Reactor
Takuya Kuwahara 1, Masaaki Okubo 1,*, Tomoyuki Kuroki 1, Hideya Kametaka 2 and
Toshiaki Yamamoto 3
1 Department of Mechanical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku,
Sakai 599-8531, Japan; E-Mails: takuya.kuwahara@gmail.com (T.K.);
kuroki@me.osakafu-u.ac.jp (T.K.)
2 Engineering and Technology Center, Niigata Power Systems Co., Ltd., 125-1 Nishishin-machi,
Ota-shi, Gunma 373-0847, Japan; E-Mail: hkame1@hotmail.com
3 Department of Electrical and Electronic Engineering, Tokyo City University, 1-28-1 Tamazutsumi,
Setagaya-ku, Tokyo 158-8557, Japan; E-Mail: yama-t@tcu.ac.jp
* Author to whom correspondence should be addressed; E-Mail: mokubo@me.osakafu-u.ac.jp;
Tel.: +81-72-254-9233; Fax: +81-72-254-9233.
Received: 25 April 2011 / Accepted: 12 May 2011 / Published: 25 May 2011

Abstract: Odor control has gained importance for ensuring a comfortable living
environment. In this paper, the authors report the experimental results of a study on the
detailed characteristics of a laminated film-electrode and a laminated film-electrode
packed-bed nonthermal plasma reactor, which are types of dielectric barrier discharge
(DBD) reactor used for odor control. These plasma reactors can be potentially used for the
decomposition of volatile organic compounds (VOCs) and reduction of NOx. The reactor is
driven by a low-cost 60-Hz neon transformer. Removal efficiencies under various
experimental conditions are studied. The complete decomposition of the main odor
component, namely, NH3, is achieved in a dry environment. The retention times are
investigated for the complete removal of NH3 in the case of the film-electrode plasma
reactor and the film-electrode packed-bed plasma reactor. The removal efficiency of the
former reactor is lower than that of the latter reactor. Mixing another odor component such
as CH3CHO in the gas stream has no significant effect on NH3 removal efficiency.
OPEN ACCESS

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Keywords: plasma; chemical reaction; nonthermal plasma; odor control; ammonia;
acetaldehyde; living environment; packed-bed

1. Introduction
Odor control has gained importance for ensuring a comfortable living environment. Previously, the
authors and other researchers have reported the implementation of a nonthermal plasma odor control
system in an animal house [1,2], odor removal from restaurants, and cigarette smoke removal [3–6]. A
nonthermal plasma is typically referred to as an atmospheric-pressure nonequilibrium plasma, in which
the gas temperature is considerably lower than the electron temperature. For this type of plasma, the
gas temperature is virtually equal to the atmospheric temperature, and the electron temperature is of
the order of 1–10 eV or several tens of thousands of K. Nonthermal plasmas can enhance chemical
reactions with low applied electrical energy.
Recently, large odor-removal aftertreatment systems using nanosecond pulsed corona plasma
combined with adsorbents or catalysts were developed for public garbage incineration plants [7],
compost factories [8,9] and NOx removal [10]. However, the capital cost involved in the development
of these systems is very high because an extremely fast pulse-switching (rising time, ~100 ns)
high-voltage power supply is required for high performance. For small apparatus such as a commercial
garbage processor [11], odor control is usually performed by using biochip technology combined with
oxidation catalysts. However, this process is extremely slow and not so effective. Therefore, low-cost,
smaller, faster and more effective odor removal systems are required. In order to meet this
requirement, the authors have investigated the use of a packed-bed plasma system for odor removal.
This plasma reactor uses packed pellets with a high relative permittivity (~10,000) [12].
In this paper, the authors report the experimental results of a study on the detailed characteristics of
laminated film-electrode and laminated film-electrode packed-bed plasma reactors, which are driven
by a low-cost 60-Hz neon transformer and can be combined with an indoor air cleaner, used for the
removal of ammonia (NH3), a typical odor component. The effects of an initial concentration and a
flow rate on removal efficiencies are studied. Further, the decomposition tendency of a mixture of NH3
and acetaldehyde (CH3CHO) is studied. Byproducts in the odor removal process are discussed.
2. Experimental Apparatus and Method
2.1. Experimental Setup
The experimental setup is shown in Figure 1. Ammonia (950 ppm) balanced with N2 and
acetaldehyde (1020 ppm) balanced with N2 prepared in cylinders and dry air supplied through a dryer
(relative humidity is approximately 4%) by an air compressor are mixed using mass flow controllers
and a gas mixer. The regulated gas is passed through the plasma reactor. The gas flow rates are set to 5,
10 and 15 L/min. After the flowing gas and plasma achieve steady state conditions, the treated gas is
sampled in a Tedlar bag through a sampling port. The concentration of NH3 is measured at the Tedlar
bag using a gas detection tube (Gastec GV-100S) whose minimum scale value is 2.5 ppm. It is noted

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that the measurement with the gas detection tube includes an inaccuracy of 1 ppm for a measured value
less than 20 ppm and an inaccuracy of 2 ppm for a measured value for 20–100 ppm. In the treatment of
the NH3 and CH3CHO mixture, a 50 mL gas sample is collected from the sampling port using a glass
syringe. The efficiency of CH3CHO removal from the sample is evaluated using a flame ionization
detector (FID) gas chromatograph (Shimadzu GC-14B).
Figure 1. Schematic diagram of experimental setup for NH3 and CH3CHO decomposition.

2.2. Plasma Reactors
The laminated film-electrode plasma reactor shown in Figure 2, which is a kind of DBD reactor, is
used for the removal of gaseous NH3 and CH3CHO. This reactor can treat higher flow rate gas than the
ordinary glass tube-type plasma reactor [12]. Figure 2(a) shows the schematic diagram of the plasma
reactor, Figure 2(b) shows the frontal and cross sectional views of the discharge unit and Figure 2(c)
shows the details of the electrodes. The plasma reactor comprises two types of film-electrodes. One
has projections of each 2 mm in size and it is used as a ground electrode as shown in Figure 2(b). The
other is covered by a polyester film which is used for dielectric barrier and it is used as a discharge
electrode. These films have a width of 100 mm. Nonequilibrium nonthermal plasma is generated
between two films and the distance between them is 2 mm. As shown in Figure 2(b), the two films are
wrapped around a capped polyvinyl chloride pipe of 60 mm diameter with alternating layers. The
laminated film-electrode packed-bed reactor is a film-type reactor whose electrodes are spaced by
2 mm. It is packed with BaTiO3 pellets (diameter, 1.0 mm; relative dielectric constant at room
temperature, 10,000). In this case, nonthermal plasma is induced among the pellets. It would be possible
to achieve the odor removal with other kind of pellets. Although some tests with other kinds of pellets
should be required as future works, the odor removal tests only with BaTiO3 are carried out in the
present study.

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Figure 2. Laminated film-electrode plasma reactor. (a) Schematic of odor removal test
section; (b) Configuration of plasma reactor (Discharge unit); (c) Detail of laminated
film electrodes.
(a)


(b)

(c)


A high AC voltage (max. Vp = 20 kV and 20 mA) of 60 Hz is applied to the reactor using a 60-Hz
neon transformer. Although there are other choices for the type of power supply such as pulsed voltage,
the AC voltage has an advantage from the point of view of cost. The input power of the neon
transformer is measured using a digital power meter (Yokogawa WT 110 E). The applied voltage
waveform is measured using an oscilloscope (Tektronix TDS380P-2GS/s) through a high voltage
divider. The current waveform is obtained by measuring the voltage to 1 k resistance which is
connected in series between the plasma reactor and the ground. The discharge power is calculated from
multiplying the voltage and current waveforms. In the results, the voltage applied to the reactor is
represented in the form of the peak-to-peak voltage (Vp-p) on the basis of the ground.
Figures 3 and 4 show the representative waveforms of applied voltage and electric current of the
film-electrode with the applied voltage of 8.5 kV and film-electrode packed-bed plasma reactors with
the applied voltage of 6.5 kV, respectively.

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Figure 3. Applied voltage and electric current in laminated film-electrode plasma reactor.
Time (s)Time (s)
Applied voltage (kV) and current (mA)
4 kV4 kV
40 mA40 mA
VV
II
10 ms10 ms
Applied voltage (kV) and current (mA)

Figure 4. Applied voltage and electric current in laminated film-electrode packed-bed
plasma reactor.
Time (s)Time (s)
Applied voltage (kV) and current (mA)
4 kV 4 kV
40 mA 40 mA
10 ms10 ms
VV
II
Applied voltage (kV) and current (mA)

Figures 5 and 6 show the input powers and discharge powers of the film-electrode and
film-electrode packed-bed plasma reactors, respectively. It is seen from these graphs that more than
24% of the input electrical power is converted into discharge plasma power at the maximum voltage.