22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Simultaneous removal of NO and SO 2 with NaClO 2 solution by using wet
electrostatic precipitator system
H.J. Yoon1, H.-W. Park1, S. Choi2 and D.-W. Park1
1
Department of Chemistry and Chemical Engineering and Regional Innovation Center for Environmental Technology
of Thermal Plasma (RIC-ETTP),INHA University, 100 Inha-ro, Nam-gu, Incheon 402-751, Republic of Korea
2
Department of Nuclear and Energy Engineering, Jeju National University, 102 Jejudaehak-ro, Jeju-si, Jeju Special
Self-Governing Province, 690-756,Republic of Korea
Abstract: Simultaneous removal of NO and SO 2 gases were examined by using wet
electrostatic precipitator which is composed of a wet chemical reactor and a plasma
electrostatic precipitator. In the wet chemical reactor, NO and SO 2 gases were absorbed
and oxidized by generated NaClO 2 aerosol particles and changed to various kind of ions.
In the plasma electrostatic precipitator, these emerged aerosol particles were negatively
charged by corona discharge and collected in the surface of anode electrode. Initial pH and
molar flow rate of NaClO 2 , and gas-liquid contact time were changed to evaluate
performances of the proposed system. The removal efficiencies of NO and SO 2 were
achieved 94.4% and 100% for gas concentrations of 500 ppmv, NaClO 2 molar flow rate of
50 mmol/min and the gas–liquid contact time were 1.25 s respectively. The total amount of
aerosol particles in the exhaust gas was reduced by electrostatic precipitator to 7.553 g/m3,
which are similar values for clean air.
Keywords: NO, SO 2 , NaClO 2 , wet chemical reactor, plasma electrostatic precipitator
1. Introduction
Sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ) have
hazardous effects on the environment such as acid rain,
photochemical smog and greenhouse effect. NO x and
SO 2 are emitted from the combustion of fossil fuel in
power plants, incinerators, and boilers. Fine particles
(PM 2.5 ) that are also harmful substance are generated by
homogeneous and heterogeneous reactions of SO 2 and
NO x in the atmosphere [1-2]. SO 2 gas can be effectively
removed by wet flue gas desulfurization (WFGD).
Selective non-catalytic reduction (SNCR) and selective
catalytic reduction (SCR) have been widely used in
various industrial fields to control NO x gas [3-4]. These
methods can control NO x and SO 2 gases, however
independent processes for treatment of NO and SO 2 gases
have problems such as a large installation area, high
operation and investment costs [5]. Therefore, a variety
of single processes have been studied focused on
simultaneous desulfurization and denitrification [6-7].
Simultaneous removal efficiencies and emission of
aerosol particles are examined to determine the optimal
conditions of wet electrostatic precipitator system.
2. Experimental setup
Fig. 1 shows schematic diagram of the wet electrostatic
precipitator system. NO and SO 2 gases were introduced
into the wet chemical reactor through the gas mixing
chamber by mass flow controllers (TSC-220, Korea
Instrument T&S, Korea) and the concentrations of NO
and SO 2 were fixed at 500 ppmv. Mixed NO and SO 2
gases were injected into the wet chemical reactor with air
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by blower at the fixed total gas flow rate of 1 Nm3/min.
NaClO 2 (78%, Duksan Reagents, Korea) was used to
oxidize and absorb of NO and SO 2 gases. Molar
concentration of NaClO 2 was changed from 0.2 mol/L to
0.5 mol/L to control the molar flow rate from
20 mmol/min to 50 mmol/min at the fixed solution flow
rate of 6 L/h. NaClO 2 solution was also injected into the
wet chemical reactor as a form of mist by the ultrasonic
humidifier (NH-5, Hwajeun Engineering, Korea). Initial
pH of NaClO 2 solution was varied from 2 to 10 by using
hydrochloric acid (36%, Dongwoo Fine-Chem, Korea)
and the solution pH was measured by a pH meter
(HI 9126, Hanna Instruments, USA). Gas-liquid contact
time in wet chemical reactor was varied from 0.25 s to
1.25 s by controlling the volume of wet chemical reactor.
Corona discharge was generated between two electrodes
which are composed of a pin type cathode and a plate
type anode, by a high voltage DC power supply (20 kV,
Plasma Technology, Korea). The electrode gap distance
between two electrodes was fixed at 24 mm. Input power
of plasma was changed from 3.8 W to 68.8 W.
3. Results and discussion
Fig. 2 shows the removal efficiencies of NO and SO 2
according to the initial pH of NaClO 2 solution. The
initial pH of NaClO 2 solution was changed from 2 to 10,
while the gas-liquid contact time, the concentrations of
NO and SO 2 , and the molar flow rate of NaClO 2 were
fixed at 1.25 s, 500 ppmv, and 40 mmol/min, respectively.
The NO removal efficiency was achieved to 99.5% with
the pH of NaClO 2 solution at 2, whereas the SO 2 removal
1
Fig. 1. Schematic diagram of the wet electrostatic
precipitator system for simultaneous treatment of NO and
SO 2 gases.
efficiency was achieved to 100% at the same condition.
This is because that ClO 2 - ion in the NaClO 2 solution was
converted to ClO 2 and chlorine gas under acidic
conditions, NO and SO 2 can be removed by additional
reactions with ClO 2 and chlorine gas [8-9]. Therefore,
the removal efficiencies of NO and SO 2 were improved
when the pH of NaClO 2 solution was acidic condition.
However ClO 2 and chlorine gas were corrosive acidic
solution and a secondary pollutant, which cause corrosion
of the wet chemical reactor and electrodes in the
electrostatic precipitator.
Consequently, pH 6 was
selected as the most appropriate pH of the NaClO 2
solution and fixed in following experiments.
Fig. 3 shows the removal efficiencies of NO and SO 2
according to the molar flow rate of NaClO 2 solution and
gas-liquid contact time in the wet chemical reactor. Initial
pH of NaClO 2 solution, concentrations of NO and SO 2
were fixed 6 and 500 ppmv, respectively. The removal
efficiency of SO 2 was achieved to 100% at the NaClO 2
molar flow rate of 50 mmol/min and the gas-liquid
contact time of 1.25 s. The removal efficiency of NO was
increased from 27.5% to 94.4% with increasing the molar
flow rate of NaClO 2 in the gas–liquid contact time of
1.25 s. Furthermore NO removal efficiency was linearly
increased as the gas-liquid contact time increased from
0.25 s to 1.25 s in different NaClO 2 molar flow rates.
However, removal efficiency of SO 2 did not increase
significantly as increasing the gas-liquid contact time
from 0.25 to 1.25 s compared with NO case.
Through, Fig. 3a and 3b were represented that NO
conversion was more effected by molar flow rate of
NaClO 2 and gas-liquid contact time in the wet chemical
reactor than SO 2 conversion. Furthermore the reaction
rate of SO 2 with NaClO 2 solution is faster than that of
NO gas in a short gas-liquid contact time.
Fig. 4 shows the total amount of aerosol particles in
exhaust gas based on the electric input power of plasma
when the NO and SO 2 concentrations of 500 ppmv, the
NaClO 2 molar flow rate of 50 mmol/min, and the NaClO 2
solution pH of 6. The total amount of aerosol particles
was remarkably reduced with an increase of the plasma
input power, because precipitation of aerosol particles in
the electrode surface was promoted with increasing
electric power of corona discharge. Therefore, when the
2
Fig. 2. Removal efficiencies of NO and SO 2 according to
the initial pH of NaClO 2 solution.
Fig. 3. Removal efficiencies of (a) NO and (b) SO 2 for
different NaClO 2 molar flow rates with variation of the
gas–liquid contact time at the fixed initial pH of NaClO 2
solution.
input power of plasma was 68.8kW, the total amount of
aerosol particles in the exhaust gas was 7.553 g/m3 which
is similar to the values for clean air.
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[7]
[8]
[9]
M. Wang, Y. Sun and T. Zhu. IEEE Trans. Plasma
Sci., 41, 312-318 (2013)
B.R. Deshwal, S.H. Lee, J.H. Jung, B.H. Shon and
H.K. Lee. J. Environ. Sci., 20, 33-38 (2008)
B.H. Yoon, L.J. Wang, S.L. Yoon and S. Kim.
Appita J., 57, 472-474 (2004)
Fig. 4. The total amount of aerosol particles in exhaust
gas based on the electric input power.
4. Conclusion
Simultaneous treatment of NO and SO 2 gases were
experimentally investigated by using the wet electrostatic
precipitator system. Removal efficiencies of NO and SO 2
were achieved to 94.4% and 100% at the NO and SO 2
concentrations of 500 ppmv and at the total gas flow rate
of 60 Nm3/h. Oxidation and absorption of NO and SO 2
gases can be enhanced by strong acidic solution of
NaClO 2 via the additional reactions with ClO 2 and
chlorine gas. NO and SO 2 removal efficiencies were
increased with increasing NaClO 2 molar flow rate and
gas–liquid contact time. The NO removal efficiency was
significantly affected by the molar flow rates of NaClO 2 ,
whereas the removal efficiency of SO 2 was not
significantly influenced because SO 2 gas reacts more
rapidly with NaClO 2 solution than that of NO gas. A
large amount of aerosol particles was emitted from the
wet chemical reactor, and the aerosol particles were
collected in the corona discharge region of the
electrostatic precipitator. The total amount of aerosol
particles in the exhaust gas were 7.553 g/m3 at the
maximum input power of 68.8 W.
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