Electrical Discharges in Liquid WaterElectrical Discharges in Liquid Water
Michael J. KirkpatrickMichael J. Kirkpatrick
Assistant Professor, SupéleAssistant Professor, Supélecc
24/06/200824/06/2008
OutlineOutline
A few words about plasma in generalA few words about plasma in general
Electrical discharges for water treatmentElectrical discharges for water treatment
• • Electric discharge in liquid waterElectric discharge in liquid water
• • Gliding Arc dischargesGliding Arc discharges
• • Hybrid water-gas discharge reactorsHybrid water-gas discharge reactors
Thermal Plasma
• Lightning and the Sun’s corona are examples of thermal plasma
1,000,000 K or 86eV30,000 K or 2.6 eV
What is a “Non-Thermal” Plasma?
• Defined as a system where free electrons have much higher energy (~12eV) than that of the bulk gas (~0.03eV)
• Can be produced in gases by an electrical discharge using AC, DC, or pulsed fields.
• To produce a discharge in liquid water, a very high and non-homogeneous electric field is required.
Pulsed electrical discharge in water
• Capacitor bank – spark gap circuit can produce pulses with ~20ns voltage rise time.
Plasma discharge in waterPulse forming circuit
Electric discharge in liquid water – physical-chemical aspects
• Chemical: produces reactive species such as hydroxyl radical, hydrogen radical, hydroperoxyl radical, hydrogen peroxide…
• Mechanical: Shockwave production• Radiative: UV and visible emissions
- Two very different discharge regimes: ‘corona’ and arc
Pulsed electrical discharge in water
StrongWeak to moderateUV emission
StrongWeak to moderateShock generation
10-5 – 10-6 s10-7 – 10-9 sPulse rise time
103 – 104 V104 – 106 VPeak voltage
103 – 104 A10 – 102 APeak current
10-2 – 10-3 Hz102 – 103 HzPulse frequency
Pulsed ArcPulsed CoronaParameter
Taken from: Locke et al. “Electrohydraulic discharge and non-thermal plasma for water treatment”, Industrial and Engineering Chemistry Research, 45, 2006.
Electric discharge in liquid water
2.5cm
Water Discharge in Motion
• Large bubbles are nitrogen purge gas for downstream hydrogen measurement.
• Very fine bubbles can be seen near the discharge (if you look very closely)
H2 and H2O2 Production
High voltage = 45 kV, Power = 67 WSolution conductivity = 150 μS/cm
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0 10 20 30
Time (min)
pp
m H
2
0
0.2
0.4
0.6
0.8
1
1.2
mm
ol H
2O
2
ppm hydrogenmmol hydrogen peroxide
Hydrogen rate = fraction hydrogen at steady state multiplied by carrier flow rate
Hydrogen peroxide rate = slope of concentration vs time line
Rates of Production of HRates of Production of H22, H, H22OO22, and O, and O22
H2
H2O2
O2 *
• HH22 : H : H22OO22 : O : O22 rates have a ratio of 4:2:1 rates have a ratio of 4:2:1
22222 246 OOHHOH
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
270 370 470 570 670 770 870 970
Wavelength (nm)
Co
un
ts
·OH
H alpha
O
Light emissions
Change in hydrogen production with electrode material
Platinum (Pt)Nickel-Chromium (NiCr)
0
500
1000
1500
2000
2500
3000
3500
4000
0 10 20 30 40 50 60
Time (minutes)
Hyd
rog
en (
pp
m)
0
0.5
1
1.5
2
2.5
Hyd
rog
en P
ero
xid
e (m
M)
ppm hydrogen
mmol H2O2
0
500
1000
1500
2000
2500
3000
3500
4000
0 10 20 30 40 50 60
Time (minutes)p
pm
Hyd
rog
en
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Hyd
rog
en p
ero
xid
e (m
M)
ppm hydrogen
mmol H2O2
Platinum
Before
After
Electrode erosion
100 micron100 micron
Nickel-Chromium
Liquid phase contaminantsLiquid phase contaminants
• • PhenolsPhenols• • TrichloroethyleneTrichloroethylene• • PCBsPCBs• • AtrazineAtrazine• • Chemical warfare simulants (H & G)Chemical warfare simulants (H & G)• • Explosives (RDX)Explosives (RDX)
In general, the application of this technique for water treatment is economically challenged, and therefore only interesting for the most recalcitrant compounds…
Physical effects - shockwaves
• Shockwaves can be Shockwaves can be focused to break up focused to break up kidney stones or kidney stones or detach zebra mussels detach zebra mussels from water intake from water intake pipes.pipes.
• Investigations are now Investigations are now being made into the being made into the treatment of ballast treatment of ballast water to kill invasive water to kill invasive species.species.
Taken from: Locke et al. “Electrohydraulic discharge and non-thermal plasma for water treatment”, Industrial and Engineering Chemistry Research, 45, 2006.
Gliding arc discharge for water treatment
Gliding arc with water spray
High voltage power supply
Water levelGround electrode
Hybrid gas-liquid discharge reactors: gas and liquid discharges
HV
HV
High voltageelectrode
Gas phaseplasma
Groundelectrode
LiquidDischarge(over exposed)
“Parallel” reactor
Thank you for your attention!