1. 1 Efficient streamer plasma generation Guus Pemen, Hans Winands, Liu Zhen, Dorota Pawelek, Bert van Heesch Eindhoven University of Technology, Department of Electrical Engineering, The Netherlands Power sources for streamer plasma generation Streamer observations Quantification of radical yields Discussion

2. 2 Gas cleaning effect by: Interaction through free radicals Using ions to charge particles to enhance their collection Electrical discharge, fast HV-pulses “Shower of electrons (<12 eV) Inelastic collisions with gas molecules >> Radicals such as O* or OH* >> chemically highly active >> easily attach/modify other molecules

3. 3 10 ns 20 ns 30 ns 40 ns fast CCD end-on view

4. 4 Efficient streamer plasma generation Creating a streamer plasma in an efficient manner (use all energy from the mains) Creating a streamer plasma that is efficient (from radical production point of view)

5. 5 ns-Pulsed power sources - i Example: TU/e resonant charging – sparkgap - TLT 3-phase 400 V 50 Hz AC continuous 5 kW 1 kV 30  s 1 kHz 500 kW 30 kV 30  s 1 kHz 500 kW 100 kV 100 ns 1 kHz 100 MW K. Yan et.al., IEEE Trans. Industry Appl., Vol. 38, No.3, May/June 2002, pp.866-872

6. 6 ns-Pulsed power sources - ii Example: TU/e 30 kW system for odor control G.J.J. Winands et.al., IEEE Trans.on Plasma Science, Vol.34, No.5, October 2006, pp.2426-2433

7. 7 ns-Pulsed power sources - iii Example: high temperature corona tar removal in syngas S.A. Nair, et.al., Ind. Eng. Chem. Res. 2005, 44, 1734-1741

8. 8 AC/DC corona generation - i Example: 2 kW TU/e pilot TU/e patents WO2005/031488 and WO2005/112212 dV/dt 1 – 3 kV/ μ s Few HV components High energy efficiency (>90 %) Good radical yield (20 % less than for pulsed corona)

9. 9 AC/DC corona generation - ii Example: investigations on TU/e – Oranjewoud system

10. 10 Efficient streamer plasma generation Power sources for streamer plasma generation Streamer observations Quantification of radical yields Discussion

11. 11 Overview of experimental set-up

12. 12 Pulse parameters and reactor configurations ParameterRange Pulse width30 - 250 ns Rise-time (20-80%)15 - 45 ns Peak voltage50 - 90 kV DC Voltage0 - 20 kV Pulse repetition rate10-1000 pps Energy per pulse0 – 2.5 J Voltage polarityPositive- negative ParameterValue Plate heigth [m]1.1 Plate width [cm]22 Plate-plate distance [cm]7.4 – 15.4 # wires1 - 7 Wire diameter [mm]0.2 - 15 Wire length [m]< 0.9 Reactor capacitance [pF]80 Max. flow used [m 3 ∙h -1 ]30

13. 13 Time-resolved side-view ICCD pictures - i G.J.J. Winands, et.al., J. Phys. D: Appl. Phys. 39 (2006) 3010–3017 Pulse width 110 ns, pulse voltage 74 kV, rise rate 2.7 kV/ns. Picture size is ~7x5 cm. White line: reactor wire. Dotted line: reactor wall.

14. 14 Time-resolved side-view ICCD pictures - i i G.J.J. Winands, et.al., J. Phys. D: Appl. Phys. 39 (2006) 3010–3017 Pulse-width 110 ns, pulse voltage -72 kV, rise rate 2.7 kV∙ns-1. Picture size is ~5.5x4 cm. White line: reactor wire. Dotted line: reactor wall.

15. 15 Streamer density Streamer velocity Streamer diameter Streamer intensity Secundary streamer length Branching, interconnecting, re-ignition Effect of repetition rate and preceding pulses Effect of DC-bias voltage

16. 16 Primary streamer velocity Results for pulse widths between 30 and 250 ns. a) Wire-plate distance fixed at 57 mm. Peak voltage: 60-70 kV. b) Voltage rise rate fixed at 1.8-2.2 kV∙ns-1.

17. 17 Efficient streamer plasma generation Power sources for streamer plasma generation Streamer observations Quantification of radical yields Discussion

18. 18 Quantification of O-radical yields - i [O 3 ] per m 3 plasma volume UV absorbtion spectroscopy [O 3, exhaust ] Gas flow + plasma volume Kinetic model (65 reactions, 17 species, RH, T) [O * ] per m 3 plasma volume Plasma volume total number of [O * ]

19. 19 Quantification of O-radical yields - ii It appears so ! Primary streamers better than secondary ? O* radical yield as function of voltage and pulse width. The rise rate of the pulses was fixed 2.2-2.7 kV/ns. DC bias: 0-20 kV. 7.0 mole/kWh corresponds to 5.3 eV/molecule. Theoretical cost to produce an O* radical is 3 eV. Thus more than half of the available energy is used to produce O* radicals Excellent yield.

20. 20 Quantification of O-radical yields - iii Primary better than secondary streamers Primary yield increases if velocity is increased (because local E-field increases and consequently so does the electron energy) O* radical yield for primary and secondary cathode directed streamers as a function of the primary streamer velocity. The error bars indicate the standard deviation.

21. 21 Quantification of O-radical yields - iv Negative polarity better for radical production However, matching is worse for negative polarity O* radical yield of primary and secondary streamers as function of the primary streamer velocity. Results for ADS and CDS.

22. 22 Reactor–modulator matching - i Calculations of load impedance, with peak voltages as indicated. The pulse width was 110 ns for all shown results. a) Typical voltage and current waveform. b) Load impedance as determined by dividing reactor voltage by the total current. c) Load impedance when using the plasma current only. The crosses indicate the moment the primary streamers have crossed the reactor-gap.

23. 23 Reactor–modulator matching - ii Comparison between positive and negative voltage polarity streamers. Wire-plate distance was 3.7 cm. Pulse width was fixed at 100 ns. a) Impedance as function of the absolute value of the reactor peak voltage. For the negative polarity the rise-rate was fixed to 1.7 2.0 kV/ns. For the positive polarity rise times of 1.6-3.0 kV/ns were used. Voltage was varied by varying DC level and charging voltage Vsg. b) Energy transfer efficiency for the same markers shown in a).

24. 24 Quantification of O-radical yields - v ?

25. 25 Efficient streamer plasma generation Power sources for streamer plasma generation Streamer observations Quantification of radical yields Discussion

26. 26 Discussion - i Primary streamers more efficient for radical production. Due to larger local electric field ? Better radical production yield for fast primary streamers. Due to larger local electric field ? Why are negative corona’s so efficient ?

27. 27 Discussion - ii Example of streamer branching and streamer interconnecting Pulse width 100 ns, rise rate 1.5 kV/ns, peak voltage +45 kV (no DC bias). Pulse width 100 ns, rise rate 2.3 kV/ns, peak voltage -79 kV (-15 kV DC bias).