S16-6
Process Development Based on Nano-Seconds Pulsed Discharge
ナノ秒パルス放電プラズマプロセスの実用化へ向けて
Takao Namihira, Douyan Wang and Hidenori Akiyama
浪平隆男, 王斗艶，秋山秀典
Institute of Pulsed Power Science, Kumamoto University
2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan
パルスパワー科学研究所 〒860-8555 熊本市中央区黒髪2-39-1
Energy efficient generation of ozone is very important because ozone is being used increasingly in a wide
range of industrial applications. In this study, ultra-short duration pulsed streamer discharges with aduration of 5 ns hava been used to produce ozone in a wire-to-cylinder electrode reactor. The triaxial
Blumlein configuration is used for the nano-seconds pulsed generator. Ozone concentration and ozone
production yield were measured at various applied voltages (50 to 70 kV), and pulse repetitions (10 to 60pps) at atomospheric pressure in oxygen and air. The experimental results showed that the ozone
concentration (g/m3) increased with increasing applied pulse voltage and pulse repetition rate. Higherozone concentrations were obtained in the oxygen-fed ozonizer than in the air-fed ozonizer. The ozone
production yield (g/kWh) was high at low ozone concentration, and higher ozone yield was obtained withlower applied voltages. Characterization maps of ozonizers based on different discharge methods(nano-seconds pulsed discharge, DBD, DBD with narrow-gap, surface discharge, pulsed corona discharge,
DC corona, superimposed discharge methods and a commercial ozonizer) were presented with oxygen-fed
and air-fed cases. A nano-seconds pulsed discharge showed the highest ozone yield in the characterization
maps for both the oxygen-fed and air-fed cases, where the highest ozone yield were 544 and 239 g/kWh in
the oxygen-fed and air-fed cases, respectively.

1. Characteristics map of Ozonizer Based on
Discharge Plasmas
Characterization maps of ozonizers based on
different discharge methods are shown in Fig. 1. InFig. 1, results of ozone generation using
nano-seconds pulsed discharge, DBD, DBD withnarrow-electrode gap, surface discharge, pulsed
corona discharge, DC corona, superimposed
discharge (surface discharge & DBD, surface
discharge & pulsed corona discharge) methods anda commercial ozonizer are displayed for bothoxygen-fed (a) and air-fed (b) cases, respectively.
In Fig. 1, the right-upper region identifies the better
performance of an ozonizer. It should be noted thatthe ozone yield resulting from the commercial
ozonizer was evaluated from the plug-in energy
while the others were examined using the dischargeenergy. In the case of the oxygen-fed ozonizer (Fig1(a)), the highest ozone yield was obtained by thenano-sconds pulsed discharge method with 544
g/kWh of peak yield in the range of 4.9-36.5 g/m3ozone ocncentration. The second highest ozone
yield resulted from DBD with a narrow-gap method
which was 500 g/kWh in the range of 10-300 g/m3
ozone concentration. The DBD method covered awide range of ozone concentration of 0.02-299
g/m3 where the ozone yield was up to 310 g/kWh.
Further low ozone concentration can be obtained bysurface discharge of 0.002-3 g/m3 where the ozone

yield was under 143 g/kWh. The DC corona
method showed very low ozone yield, and thepulsed corona discharge showed a narrow range ofozone concentration. The result of thesuperimposed discharge method was completelycovered by the area of the DBD method. The ozone
yield of an oxygen-fed type commercial ozonizer
using DBD with a narrow-gap method was 1.9g/kWh at 16 g/m3 of ozone concentration. Since thislow energy efficiency is mainly due to power
consumption in the PSA oxygen generation unit,
the ozone yield without the PSA unit was alsomeasured, and the result was 30.5 g/kWh at 16 g/m3.
For the air-fed ozonizer (Fig. 1(b)), the highestozone yield was also obtained by the nano-seconds
pulsed discharge method with 239 g/kWh of peakyield in the range of 2.2-18.3 g/m3 ozone
concentration. The second highest ozone yield
resulted from DBD with a narrow-gap method
which was 175 g/kWh in the range of 0.3-62 g/m3
ozone concentration. The DBD method seems to be
not as efficient as the pulsed corona method in theair-fed case. The ozone yield by the pulsed corona
method showed a wide range of ozone
concentrations, typically 0.001-28 g/m3 with amaximum ozone yield of 130 g/kWh. Finally, theozone yield of an air-fed type commercial ozonizer
using the DBD with a narrow-gap method was 17g/kWh at 10 g/m3 of ozone concentration.

The reason why the nano-seconds pulsed
discharge gave the highest ozone yield is due to its
unique discharge phenomena. Fig. 2 shows streak
images of (a) a pulsed discharge and (b) anano-seconds pulsed discharge in a coaxial
cylindrical electrode geometry. From Fig. 2(a), adischarge with a pulse duration of 100 ns shows
two discharge phases: a streamer discharge which
initiates in the vicinity of the central electrode andpropagates toward the outer electrode; and aglow-like discharge which is generated after fulldevelopment of the streamer discharge. It was also
observed that the plasma impedance was different
for the streamer and the glow-like discharges.
Moreover, a rise of the gas temperature occurred
during the glow-like discharge phase. These factors
could induce energy losses due to the impedancemismatching between the pulsed power generator
and discharge reactor, with gas thermalization fromplasma-enhanced chemical reactions during gas
treatment. On the other hand, the discharge with apulse duration of 5 ns, shown in Fig. 2(b), indicatesthat the discharge history finishs before it shifts to
the glow-like discharge phase. Consequently, theimpedance matching between the power generator
and discharge reactor can be improved and the gas
heating problem can be minimized.
NS Pulsed Streamer
Discharge Method

Ozone yield, g/kWh600
500
400

DBD with narrow-gap(0.05-0.8mm)

DBD
SuperimposedDischarge

DC Corona(Pos.&Neg.)

Corona300 Pulsed
Discharge

200 Surface
Discharge

Commercial
Ozonizer

10000.001 0.01

0.11101001000

Ozone concentration, g/m3(a) Oxygen-fed
Ozone yield, g/kWh

250

Nano-Seconds
Pulsed Discharge

200

DBD with narrow-gap(0.2-0.8mm)

150
DBD

100

Commercial
Ozonizer

Pulsed Corona
Discharge

50
00.0010.010.1

110100Ozone concentration, g/m3(b) Air-fed
Figure 1. Characteristics map of ozonizers based on
different discharge methods.

Brightness

Central rod(a) Pulsed duration of 100 ns.
BrightnessCentral rod(b) Pulse duration of 5 ns.
Figure 2. Streak images of (a) a pulsed dischargeand (b) a nano-seconds pulsed discharge in a
coaxial cylindrical electrode reactor.
2. Conclusion
Characterization maps of ozonizers based on
different discharge methods (nano-seconds pulsed
discharge, DBD, DBD with narrow-gap, surface
discharge, pulsed corona discharge, DC corona,
superimposed discharge (surface discharge & DBD,
surface discharge & pulsed corona discharge)
methods and a commercial ozonizer) werepresented for the oxygen-fed and air-fed cases. The
following conclusions have been deduced:
A nano-seconds pulsed discharge showed thehighest ozone yield in the characterization maps forboth the oxygen-fed and air-fed cases.
References[1] T. Namihira, D. Wang, T. Matsumoto, S. Okada, H.
Akiyama, “Introduction of nano-seconds pulsed
discharge plasma and its applications”, IEEJ
Transactions on Fundamental and Materials, Vol.129,
No.1, pp.7-14, 2009.
[2] D. Wang, T. Matsumoto, T. Namihira, H. Akiyama,“Development of higher yield ozonizer based on
nano-seconds pulsed discharge”, Journal ofAdvanced Oxidation Technologies, Vol.13, No.1,
pp.71-78, 2010.