Mass balance investigation of sulfur atoms in plasma desulfurization

Mass balance investigation of sulfur atoms
in plasma desulfurization process
Shogo Hosoi1, Daisuke Nishioka1, Kazuhiro Takahashi1,2, Kohki Satoh1,2, and Hidenori Itoh1
1Division
of Information and Electronic Engineering, Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Japan
2Center of Environmental Science and Disaster Mitigation for Advanced Research, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Japan
Email: [email protected]
1.Introduction
3. Results and discussion
Sewage treatment process
(1) H2S decomposition rate
Secondary
sedimentation Disinfection
tank
Aeration tank
100
decomposition rate of H2S [%]
Primary
sedimentation
tank
Al2O3 98.0%
80
sewage
Cl
Decomposition rate of H2S
66.4% with glass balls
98.0% with Al2O3 balls
glass 66.4%
60
40
Organic sludge
H
C
H
Fuel
(Removal of H2S)
O
O C
H
H
H
C
H
H
Sludge digester
Anaerobic digestion
S
O
O C
H
H
H
CH4/CO2/H2S = 60/40/0.08%
3H2S +Fe2O3 → Fe2S3 + 3H2O
Gas turbine generator, etc.
(21 - 23 MJ/Nm3)
0
0
20
1.0x10
Anaerobic digestion by bacteria is a process to convert organic sludge into a digestion gas.
 The digestion gas has the half of the heating value of city gas, so that it is used as fuel for micro gas
turbine and heating.
Dry desulfurization method (3H2S + Fe2O3 → Fe2S3 + 3H2O )
Desulfurization method without the desulfurizing agent is needed for the economical point of view.
0.4
H
C
H
H
S
H
H
M
M+
Ion
M*
Electron
Excited molecule
H
300x10
1.0
1.5
2.0
2.5
(CH3)2S (Dimethyl sulfide)
3.0
3.5
retention time [min]
4.0
4.5
5.0
5.5
6.0
3
GCMS-QP2010Plus
C2H5CHO
(Propionaldehyde)
C4H9OH (Butyl alcohol)
(CH3)2CO (Aceton)
200
CH3COOH (Acetic acid)
C2H5SCH3 (Ethyl methyl sulfide)
CH3OH
150
CH3CH2COOH (Propionic acid)
C3H7OH (2-Propanol)
C2H5OH (Ethyl alcohol)
100
C2H6O3 (Methyl mesylate)
H2O
0
2.0
3.0
4.0
5.0
6.0
7.0
retention time [min]
8.0
9.0
10.0
11.0
12.0
H
O
O C
H
eM+
e-
e-
C
e-
M
M Gas molecule
M
(CH3)2O (2-Butanone)
Dielectric Dielectric balls
M+
H
CH3COOH (Acetic acid)
(3) Mass balance for sulfur atoms with and without PB-DBD
Desulfurization
PB-DBD
O
O C
H
C3H7OH (n-Propanol)
CS2 (Carbon sulfide)
H2S (Hydrogen sulfide)
CH2O (Formaldehyde) CH3CHO (Acetaldehyde)
CH3OH (Methanol)
glass
Al2O3
Sulfur compounds, i.e. SO2, CH3SH, CS2, COS, (CH3)2S, C2H5SH, and C2H5SCH3, are detected as by-products,
and those concentrations with Al2O3 balls are lower than those concentrations with glass balls.
Proposed Desulfurization process
H.V.
CH3SH (Methyl mercaptan)
C2H5OH (Ethanol) (CH ) CO (Acetone)
3 2
C2H5CHO (Propionaldehyde)
C2H5SH (Ethyl mercaptan)
50
This method requires a desulfurizing agent, and generates by-products.
Metallic
electrode
CO2
0.0
0.5
intensity [a.u.]
Desulfurization is needed as a pre-process of the digestion gas usage.
GCMS-QP2010SE
n-C4H10 (Butane)
H2O, SO2
0.6
250
Digestion gas
CH4, CO2
0.2
Problem
 The digestion gas contains H2S, which is toxic & corrosive, and H2S is converted into SO2, which
causes air pollution, by combustion.
80
6
0.8
Potential
40
60
time [min]
Decomposition rate of H2S with Al2O3 balls is
1.5 times higher than that with glass balls.
(2) Chromatograms of the off-gas by GCMS analysis
intensity [a.u.]
Desulfurization
Digestion gas
20
M*
S
M
Formation energy
Excited molecule > 6 eV
Bond dissociation energy
H-SH
: 3.95 eV
• Active and energetic species, which can initiate dissociation reaction, are generated in discharge
plasma, decomposing H2S.
Objective
To investigate the safety and effectiveness of the discharge plasma desulfurization
 We desulfurized an artificial digestion gas using a packed-bed dielectric barrier discharge (PB-DBD).
 We investigated by-products and estimated mass balance for sulfur atoms based on the results.
2. Experimental apparatus and conditions
W/O PB-DBD
The number of sulfur atoms [ppmS] =
 PB-DBD reactor
 High voltage electrode
 Earthed electrode
 Outer mesh
 Dielectric balls
 Glass or Al2O3 balls
Inner rod
electrode
stainless steel
f 2 mm
Dielectric balls
 Analysis of gas
 The off-gas of the PB-DBD reactor is
sampled and analysed by a gas
chromatograph (GC) equipped with a
thermal conductivity detector, a gas
chromatograph mass spectrometer
(GCMS), and a Fourier transform
infrared spectrophotometer (FTIR)
equipped with a gas cell.
Glass tube
I. D.
f 20 mm
O. D. f 22 mm
length 250 mm
glass balls
er = 7.5
f 3.0 mm
Neon Transformer
 Vp-p = 13 kV
 Input power
22 W
 Input voltage
50 - 60 V
Input H2S
Output H2S
CH3SH
SO2
COS
CS2
Others( (CH3)2S, C2H5SH, C2H5SCH3) )
& deposition
Glass
578
194
47
88.4
26.8
3.0
218.8
Al2O3
578
7.6
39.8
0
14.5
2.7
527.9
 In contrast, approximately 90 ppmS of SO2 is generated only when the glass balls is used as dielectric
balls. This indicates that the discharge plasma treatment with Al2O3 balls is safety.
 Mixture ratio
 An AC high voltage is applied between
the electrodes, generating the PB-DBD.
 Input power to the PB-DBD reactor is
22 W.
Dielectric material
 Approximately 40 ppmS of CH3SH and 3 ppmS of CS2 are generated with glass and Al2O3 balls by the
discharge plasma treatment.
 Gas conditions
 High voltage application
The number of sulfur atoms in H2S and by-products
×
The concentration of each substance [ppm]
Variations in the number of sulfur atoms with and without PB-DBD.
 Inner rod
CH4/CO2/H2S = 60/40/0.058%
 constant flow rate : 0.2 L/min
W/ PB-DBD
Outer mesh
electrode
aluminum
16 meshes
130 mm
Packed-bed dielectric barrier discharge
GC
GCMS
490 Micro GC (Agilent)
• GCMS-QP-2010SE (Shimadzu)
• GCMS-QP-2010Plus (Shimadzu)
Column
 Molsieve 5A
H2, O2, N2, CH4
 Pora Plot Q
H2S, CO2
Column
 CP-Sil 5CB for Sulfur
 DB-WAX
 The concentration of COS decreases in the case of Al2O3 ball filling.
 Although the concentrations of (CH3)2S, C2H5SH and C2H5SCH3 have not been measured, these
concentrations are expected to be low because these peak areas of the chromatogram are small.
This may suggest that the some of sulfur atoms containing in H2S deposits on the electrodes and the wall
of the discharge reactor as solid.
Plasma desulfurization with Al2O3 balls is safe and effective since there are high
H2S decomposition rate, no SO2 production, and high desulfurization rate.
4. Conclusions
An artificial digestion gas is desulfurized using a PB-DBD, and the
desulfurization characteristics are discussed based on mass balance for
sulfur atoms.
 The decomposition rates of H2S are 66.4% and 98.0% with glass balls and Al2O3
balls, respectively.
 It is found that SO2, CH3SH, CS2, COS, (CH3)2S, C2H5SH, and C2H5SCH3 are
produced as sulfurous by-products.
 Plasma desulfurization with Al2O3 balls is safe and effective.

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