S16-5
The Current State and Issues of Electron Beam Flue Gas Treatment
電子ビームによる排ガス処理技術の現状とその課題
Teruyuki Hakoda
箱田照幸
Japan Atomic Energy Agency, Quantum Beam Science Center
1233, Watanuki, Takasaki, Gunma 370-1292, Japan
日本原子力研究開発機構 量子ビーム応用研究センター 〒370-1292 群馬県高崎市綿貫町1233
An electron beam flue gas treatment is introduced for removal of nitrogen and sulfur oxides (NOx, SOx) ina flue gas from a coal-fired boiler, decomposition of dioxins in a flue gas from a municipal solid waste
incinerator, and oxidation of volatile organic compounds (VOCs) in a flue gas from painting factories as
typical application of EB technologies for environmental protection. Their current issue is also discussed
for an industrial and commercial scale plant.

1. Introduction
Electron beams (EBs) are one of the advanced
technologies for treating environmental pollutants.
This technology is based on oxidation reactions
with active species produced by the irradiation tomedia. When irradiated to air, many active species
such as OH radicals, O atoms, and N2+ are produced.
Among the species, OH radicals are most important
active species that can oxidize dilute pollutants in agas stream. In the present report, the EB treatmentof nitrogen and sulfur oxides (NOx, SOx), dioxins,and volatile organic compounds (VOCs) in fluegases are introduced as an application of EB
technology for environmental protection. Theircurrent issue is also discussed for an industrial andcommercial scale plant.
2. Removal of NOx/SOx
Nitrogen and sulfur oxides (NOx and SOx) influe gases from a coal-fired boiler will cause acidrain. When the flue gases are irradiated with EBs,NOx and SO2 are simultaneously oxidized into
HNO3 and H2SO4 in the gas phase. These acids arechanged into particulate (HN4)NO3 and (NH4)2SO4
through the neutralization with ammonia (NH3)
injected into the flue gases before EB irradiation.
These particulate products are removed from thegas phase at an electrostatic precipitator (ESP) andused as an agricultural fertilizer.
Pilot-scale test was performed for a flue gas of
12,000 Nm3/h in Japan, where sufficient removal
efficiency of NOx and SOx was obtained, as shownin Fig. 1. Depending on initial concentrations andgas temperature, approximately 80% of NOx andmore than 94% of SOx were removed at a dose of
8.3 kGy(=kJ/kg) [1].
Based on these results, industrial-scale plants are
now working at Chengdu (300,000 m3N/h) andHangzhou (305,400 m3N/h) in China using
accelerators (800 kV/400 mA× 2), Pomorzany
Thermoelectric Power Station (270,000 m3N/h) in
Poland using accelerators (700 kV/370 mA×4) [2].

Fig. 1. Removal efficiency of NOx and SOx[NOx]0= 220-240 ppm, [SOx]0=650-950 ppm,
Temperature= 62-67℃

3. Decomposition of Dioxins
Dioxins are a very toxic to human body from therespect to endocrine disrupting character,carcinogenicity, and mutagenicity. They include
polychlorinated dibenzo-p-dioxins (PCDDs) andpolychlorinated dibenzofurans (PCDFs). Municipal
solid waste incinerators (MSWIs) are the main
source for the dioxin emission. The reduction of
their emissions has been required for incineration.
Pilot-scale test was conducted in Japan todecompose/detoxify dioxins in a flue gas from theMSWI at a temperature of 200°C [3]. The test plant
was constructed at a site of the Takahama Clean
Center treating 450 t (150 t × 3 furnaces) of solid
wastes in 1 day. The incineration of 150 t of wastes
generated approximately 40,000 m3 N/h flue gas. A
flue gas of 1,000 m3N/h for the test plant wasobtained downstream of ESP and then irradiatedwith EBs using an electron accelerator (300 kV/40mA). As shown in Fig. 2, more than 90%
decomposition of PCDD/Fs was obtained at a doseof about 14 kGy. An annualized cost for EB
systems was estimate to be 7% lower than that for
bag-filter systems.

shown in Fig. 3. The yield of CO2 to COx increased
from 52–60% to 83–89% by the catalytic treatment.
Based on the obtained results, the catalyticoxidation was profitable to reduce total initialinstallation cost for purification of VOC gas stream.

80604020005101510080604020020

Mineralization
ratio (%)

Removal ratio (%)

100

Dose (kGy)
Fig. 2. Decomposition efficiency of dioxins

4. Oxidation of VOCs
Volatile organic compounds (VOCs) have beenused in various industries as solvents, washingreagents and basic materials for chemical synthesis.
The emission of VOCs to the atmosphere causes
toxic photochemical smog. Several efforts havebeen made to reduce VOC emission by installing
treatment technologies, reducing the quantities used,and recycling. VOCs can be treated by twomethods: they can be recovered by adsorption,absorption, and condensation, or can be eliminatedby thermal incineration, catalytic incineration, andnonthermal plasma (NTP). Electron beam (EB) andelectric discharge techniques are used to create
NTPs that can treat VOCs with concentrations lessthan 100 ppmv at a flow rate of 10−1–105 Nm3/h [4].
Under EB irradiation, VOCs are attacked by OH
radicals to produce organic acids and aldehydes asgaseous and particulate intermediate irradiation
byproducts. Since these products will cause
photochemical smog, they should be oxidized into
COx (CO2, CO) through mineralization reactions.
Some studies on the EB treatment combined withcatalytic oxidation process have demonstrated theenhancement of their mineralization. We observedthat an ozone decomposition catalyst was one ofappropriate catalysts combined with EBs at alaboratory study [5].
A pilot-scale test for decomposition of VOCs in agas stream (500 m3N/h) was performed using anEB/MnO2 system using an electron accelerator (160kV/50 mA) [6]. A combined MnO2 bed enhanced
the removal of VOCs and the mineralization ofVOCs and its irradiation organic byproducts asFig. 3. Removal ratio of toluene (, ) and xylene (,) and the mineralization ratio (, ) with and without
the catalytic treatment as a function of dose for 5-ppmv
toluene/xylene/air mixture.

5. Current issue of EB treatments
An electron accelerator is a key component of EB
flue gas technology. The installation of a few
industrial-scale plants were cancelled, because of
fatal accidents happened at high-voltage parts ofused accelerators. Accordingly, high-power andstable accelerators are necessary for the application
to industrial and commercial flue gas treatment.
The price of the accelerator is also importantfactor to realize the EB flue gas treatment. The costof self-shielding accelerators is about 1/3 of that ofhouse-shielding accelerators at the same power. The
use of such self-shielding accelerator is one ofsolutions to reduce the capital cos of EB flue gas
treatment.
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