S16-2Emission Aftertreatment for Combustion Systems Using Nonthermal Plasma
Combined with Chemical Processes
大気圧プラズマ複合プロセスによる燃焼機器排ガス処理
Masaaki Okubo, Takuya Kuwahara, Tomoyuki Kuroki, and Hidekatsu Fujishima
大久保雅章，*桑原拓也，黒木智之，藤島英勝
Department of Mechanical Eng., Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan*Nippon Institute of Technology, 4-1 Gakuendai, Miyashiro, Minamisaitama, Saitama 345-8501, Japan
大阪府立大学，*日本工業大学
The authors have been carrying out the applications of nonthermal plasmas to emission control forcombustion systems such as marine diesel engines or bio-fuel boiler, and now some are on commercial
stages. In this lecture, pilot-scale apparatus and experimental results concerning these systems arediscussed. We achieved highest removal efficiency of NOx reduction greater than 100 g (NO2)/kWh when
the nonthermal plasma is combined with other chemical processes (adsorption or wet chemical scrubbing).
The efficiency is approximately ten-times higher than that in the case with plasma application only.

1. Introduction
One of important and successful environmental
applications of atmospheric-pressure corona
discharge or plasma is electrostatic precipitator(ESP), which have been widely used for coal- or
oil-fired boilers in electric power plants andparticulate matter control emitted from glass
melting furnace system, etc. In the ESPs, steadyhigh voltage is usually applied to a pair ofelectrodes (at least, one of these has sharp edge).
Unsteady pulsed high voltage is often applied forthe collection of high-resistivity particulate matter(PM) to avoid reverse corona phenomena which
reduce the collection efficiency of the ESPs. It was
found that unsteady high voltage can treat
hazardous gaseous components (NOx, SOx,hydrocarbon, and CO) in the exhaust gas, andresearches were shifted from PM removal tohazardous gases aftertreatment with unsteadycorona discharge induced plasmas.
In our laboratory, we have tried to develop
nonthermal-plasma environmental applications
technology since 1998. Main research topics are as
follows: diesel engine emission control, boilers
emission control, NOx removal for glass melting
furnace, VOC control from factories, odor anddioxin controls from garbage incinerators, CO2 andPFC emission and moisture controls in various
environments, and indoor electric air cleaner. Our
all papers are listed in [1]. In the lecture, recent
results on diesel engine and boiler emission
controls are presented among these topics.
2. Marine Diesel Engine Emission Control [2-5]Figure 1 shows the experimental setup for theaftertreatment system in the marine diesel engine(6DK-20e, output power = 1071 kW, Daihatsu
Diesel MFG Co., Ltd, fuel: A-heavy oil or marine
diesel oil). In this system, the combination ofadsorption and the NTP is used for reduction ofNOx. The exhaust gas emitted from then engine isfirst separated and approximately 13% of thebypassed gas the flow rate of which is controlled by
the flow regulation valve passes through a set ofceramics diesel particulate filters (DPFs). Morethan 95% of the PM in the exhaust gas is captured
in the DPFs. The accumulated PM in the DPF istreated by nonthermal plasma-induced ozone (O3)
injection technology [3, 5]. After this process of thePM removal, NOx in the exhaust gas is treated byNTP combined with repeated adsorption anddesorption processes. In the adsorption process, foran effective NOx adsorption to adsorbents, theexhaust gas is cooled from 270C down toTo stackFlowregulation
valve

25A

Cooler

NTP generators (5.4 kW×4)

NTP generators

150A
25A

400A

Ozonizer(3.1 kW)

Ball valve
Adsorption chamber
Marine diesel engine (1071 kW)

Liquid nitrogen
150A
DPF
CoolerExhaust in adsorption process
Exhaust in desorption process

N2 flow

Fig. 1. Schematic diagram of experimental setup for theaftertreatment system in the marine diesel engine

NOx (g(NO2)/h)

2000
2000
1800
1800
1600
1600
1400
1400
1200120010001000
800
800
600
600
400
400
200
20000

Ads.: Load 75%, Des.: Load 50% (N2: 11.1 Nm3/h)

2nd

3rd

Ads.

Des.

Ads.

115min86min

125min

4th9th

10th

Ads.

Des.

Ads.

Des.

Ads.

Des.

76min 110min

58min

105min 42min

225min

72min

Des.

NOx in untreatedexhaustDesorbed
NOx

ReducedNOx

Adsorbed
NOx

NOx fromtreatment system

300
1600 1700
1700 1800
1800 1900
1900 2000
2000
300 400
400 500
500 600
600 700
700 800
800 1500
900 1600
Elapsed time (min)Fig. 2. Time-dependent NOx emission from the aftertreatment
system for the marine diesel engine

approximately 45C with the water-cooling typecooler. An adsorption chamber that containsadsorbents adsorbs NOx of 92% in maximum.
Finally, the exhaust gas is flowed out from a stack.
In the desorption process, after the valves arecontrolled, N2 gas of lower flow rate of 11.1 ~ 22.2
Nm3/h supplied from liquid N2 cylinder passes
through the chamber. The direction of the N2 gas isopposite to that of the exhaust gas in the adsorption.
Simultaneously, the chamber is heated up by thewaste heat of the exhaust gas. As a result,high-concentration (typically 1% = 10000 ppm)
NOx flows out from the chamber, and introduced to
the NTP reactors of total 21.6 kW in maximum.
Figure 2 shows a time-dependent NOx emission
before and after the gas passes through theaftertreatment system for operation cycles 2 ~ 4, 9,
and 10. Exhaust gas is continuously treated during
these repeated cycles. In this graph, the mass flowrate of NOx is taken in the vertical axis evaluatedbased on the molecular mass of NO2 with the unitof g(NO2)/h. Furthermore, the untreated NOx isindicated by white circles with lines, and treatedNOx is indicated by black circles with lines. NTP isapplied only in the desorption processes, and theinput power to the NTP generator is 21.6 kW in thecycles 2 ~ 4 and 12.0 kW in the cycles 9 and 10. It
is known this graph that large amount of NOx istreated. At 10th cycle, the highest system energy
efficiency among these cycles of system = 161g(NO2)/kWh is achieved. Application of the highest
recorded energy efficiency to the requirement of theIMO (International Maritime Organization)
emission standards from Tier II to III corresponds
to only 4.3% (= 6.9 / 161  100) of the engine
output power.
More detailed description on the pilot-scale
experiment was explained in our recent paper [2].

Fig. 3. Plasma hybrid clean  boiler system

3. Bio-fuel Boiler Emission Control [6-9]The results for the pilot-scale application of theNTP to bio-fuel boiler (Fig. 3, steam generation
rate = 2.5 ton/h) are presented in the lecture.
Acknowledgments
This work was supported by the Regional R&D
Resources Utilization Program in JST and JSPS
KAKENHI Grant Number 24246145 and 249848.
References[1] M. Okubo, paper list by Google Scholar,
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Process. 34(1) (2013) 65.
[3] T. Kuwahara, K. Yoshida, K. Hanamoto, K. Sato, T.
Kuroki, T. Yamamoto, and M. Okubo: IEEE
Transactions on Industry Applications 48(5) (2012)1649.
[4] T. Kuwahara, K. Yoshida, K. Hanamoto, K. Sato, T.
Kuroki, T. Yamamoto, and M. Okubo: J. Japan
Institute of Marine Engineering 47 (2012) 379.
[5] M. Okubo et al.: Plasma Chem. Plasma Process.
28(2) (2008) 173.
[6] H. Fujishima, K. Takekoshi, T. Kuroki, A. Tanaka, K.
Otsuka, and M. Okubo: Applied Energy 111 (2013)394.
[7] H. Fujishima, Y. Yoshioka, T. Kuroki, A. Tanaka, K.
Otsuka, and M. Okubo: IEEE Transactions onIndustry Applications, 47(5) (2011) 2210.
[8] H. Fujishima, T. Kuroki, T. Ito, K. Otsuka, T.
Yamamoto, K. Yoshida, and M. Okubo: IEEETransactions on Industry Applications, 46(5) (2010)1707.
[9] H. Fujishima, A. Tatsumi, T. Kuroki, A. Tanaka, K.
Otsuka, T. Yamamoto, and M. Okubo: IEEE
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