1
PlasTEP Final Conference
5. / 6. 12. 2012
Plasma for Gas Cleaning
Approaches by a Process
Engineer
Ulrich Riebel
Chair of Particle Technology
BTU Cottbus
Current Problems in Electrostatic Precipitation (10th Nordic Filtration Symposium, Trondheim 2006)
Transport of
Ionized Molecules
Ozone
Gas-to-Particle
Conversion
Electric Wind
„BEGA“
Corona Onset
Effects cm1011el
Particle
Reentrainment
„ABREA“
Corona Quenching
by space charges
cm10 4el
Back Corona
A Combination of Biofilter & ESP for Gas Cleaning Diss. Robert Mnich, BTU Cottbus, 2009
BEGA =
Bio – Elektrischer Geruchs–
Abscheider
Simultaneous removal
of aerosols and
organic vapours by
combination
of ESP and
biofilter
BEGA-subtopic: Direct Ionic Transport Does the corona discharge contribute significantly to VOC
abatement?
Experimental Evidence
• Atmosphere saturated with
various (organic) substances
• Controlled humidity and temp.
• Influence of discharge polarity
• Measurements of discharge
current and mass of deposit on
precipitation electrode (p. e.)
Substance
gnd
p.e. c.e.
+
-
Spannungs- Stromdiagramm
0,00
5,00
10,00
15,00
20,00
25,00
30,00
35,00
40,00
45,00
50,00
0,0 5,0 10,0 15,0 20,0 25,0
U in kV
I in
µA
Campher 33% rel. Luftfeuchte Raumtemperatur pos. Korona
Campher 33% rel. Luftfeuchte Raumtemperatur neg. Korona
rel. Luftfeuchte 33% Raumtemperatur neg. Korona
rel. Luftfeuchte 33% Raumtemperatur pos. Korona
Neg. Corona
Pos. corona –
current uptake
is reduced
significantly
Neg. corona –
no effect from
camphor.
Effect of VOCs on current-voltage characteristic of corona
This effect is
explained by the specific
attachment of VOCs to
the gas ions, leading to a
change of ion mobility
Direct Ionic Transport Exp. Evidence with Salol
A deposit of fine
particles is formed on
the precipitation
electrode 200x Vergrößerung 200 x Vergrößerung
OH
C - O
O
Influence of VOCs on Corona Discharge
• VOCs bind specifically to gas ions, forming ions of
lower mobility
• This is indicated by a lowered current uptake
• Hence ionized VOCs are transported to the
precipitation electrode at high velocity, v=50m/s
• Unfortunately, at typical ESP conditions, the corona
current (< 1 mA/m²) can only remove ppb concentra-
tions
….nevertheless…
Abscheidung vom Isopren im Elektroabscheider
0
2
4
6
8
10
12
14
16
18
20
15:47:15 15:48:41 15:50:08 15:51:34 15:53:01 15:54:27 15:55:53 15:57:20
Zeit
Ko
nzen
trati
on
vo
m Iso
pre
n [
pp
m C
3]
Konzentration vom Isopren im EA
ohne Spannung: "0kV"
Konzentration vom Isopren im EA
mit Spannung: "-30kV"
ESP – Removal of Isoprene by Corona Diss. Robert Mnich, BTU Cottbus 2009
Nevertheless…
Some VOC´s can be removed quite efficiently by
corona discharge in an ESP
Electrostatic Precipitator – Removal of Isoprene by Corona Discharge Diss. Robert Mnich, BTU Cottbus 2009
Trocken-EA, uLR=0,041m/s (tVWZ=7,2s), U=22 kV, negative/positive Polarität
24
,8
21
,9 37
,9 54
,1
12
1,0
3,2
3,3 7,0 2
0,1
49
,6
31,7
42,4
36,6
28,7 4
9,6
152,2
166,8
241,4 271,5
332,6
48
68
5250
29
96 97 95
89
80
0
40
80
120
160
200
240
280
320
360
400
48 68 78 107 171 71 94 147 184 249
Isopren-Rohgaskonzentration [mg/m³]
Iso
pren
-Re
ing
asko
nz. [m
g/m
³]
0
10
20
30
40
50
60
70
80
90
100
Ab
sch
eid
un
g V
OC
s [
%]
FID, Reingas [mg/m³] SMPS, Reingas [mg/m³] Abscheidung [%]
"positive Korona" "negative Korona"
0,0E+00
5,0E+03
1,0E+04
1,5E+04
2,0E+04
2,5E+04
3,0E+04
3,5E+04
4,0E+04
4,5E+04
5,0E+04
10 100 1000
x [nm]
C# [
#/c
m3]
20 ppm
23,5 ppm
31,1 ppm
48,4 ppm
60,6 ppm
81,9 ppm
300 ppm
Trend bei steigender Isoprenkonzentration
im Rohgas
Electrostatic Precipitators and VOC
reduction – Conclusions
• ESP performance is signifantly influenced by VOCs
• Some VOCs are removed significantly by oligomerization + particle formation behind the ESP
• Significant emission of intermediate reaction products and aerosols
• Hence typically, ESPs are not suited for VOC removal
In one of our next projects….
PLASMA appeared to be the last hope
• Off-gas from smoking
• Wet scrubber does not reduce VOCs sufficiently
• Postcombustion not wanted
…so we collected a lot of literature on plasma
reactions and built a lab reactor for a feasibility
study.
We had to learn some lessons about…
• Energy input may be calculated from Lissajous measurement or from Manley formula…
• The results are quite different
• Calorimetric measure-ment confirm Lissajous results
Plasma – measurement of energy input
BA Roman Eibauer, BTU 2011
Lissajous
Manley
„Cold Plasma“ – Specific Energy Input and
Reactor Temperature I
• Many Cold Plasmas are not quite so cold…high energy inputs:
1 J/ltr ~ 1 °C temperature rise
Magureanu et al. Appl.Catalysis B, 2007
F. Holzer, U. Roland H.D. Kopinke, UFZ-Ber. 1998/99
Kim et al. Int. J. Plasma Env. Sci. & Technol. 2007
„Cold Plasma“ – Specific Energy Input and
Reactor Temperature II
• Temperature effects on plasma
reaction kinetics?
• Research reactors should have a
defined temperature…
heating/cooling
• Technical (big) reactors are
adiabatic…
the transition to thermal
combustion will occur beyond
300 ..500 J/Ltr.
adiabatic
Kim et al. Int. J. Plasma Env. Sci. & Technol. 2007
- Small lab reactors – significant
temperature losses
- Many reference experiments
were run at a non-defined
temperature
DBD plasmas…we still have the aerosol problem
450 ng/m³ @ 15 kV
140 ng/m³ @ 17,5 kV
Aerosols
remain after VOC oxidation
and require more energy
input
Plasma was not a full success…
• Complicated interaction of
temperature, humidity and
catalysts decisive for energy
input.
• Methane was not oxidized
efficiently and we could not
find a catalyst for this task.
• Compared to wet scrubber,
comparable methane emission
but higher energy consumption
Methane above
TOC limit
TiO2 catalyst
active above
85°C
BA Simon Marschall, BTU 2012
DBD plasmas…what we were missing
• Kinetic constants for diverse VOCs and reaction conditions
• Many reactor designs, but almost no comparative data on reactor efficiency
• Generally accepted „model substances“ for testing reactor efficiencies
• More knowledge about byproducts, CO, phosgen, heterocyclic VOCs, particle production
Kim et al, J. Phys. D:
Appl. Phys 2005, 1292
Magureanu et al. Appl.
Catalysis B, 2007
Plasma für Gas Cleaning - Outlook
- Energy efficiency is critical, plasma will be restricted to
very low concentrations and special applications
+ Compact reactors/short residence time
+ Function without additional media (water, gas…)
+ No residues (ideally)
+ A natural process – atmospheric oxidation – is imitated
++ A lot of research is needed!
The End
Plasma in Gas Cleaning
Specific transport of ionized molecules
Could it be relevant in gas cleaning?
ESP - typical current density: I ≤ 1 mA/m2
elementary charge e = 1,60210-19 As
typical electrode spacing a = 0,1 m
typical residence time = 1 s
cC
a
τ
e
I
gasprocessed volume of
es (ions)argchnumber of
315 /m1025,6Cc
mC25107,2
0VΑv
Ν
gasvolume of
moleculesnumber of ppbv4ˆ
9104
mC
cC
Strom- Spannungsdiagramm
0,00
5,00
10,00
15,00
20,00
25,00
30,00
35,00
40,00
45,00
50,00
0,0 5,0 10,0 15,0 20,0 25,0
U in kV
I in
µA
1- Butanol 33% rel. Luftfeuchte 20°C pos. Korona 1- Butanol 33% rel. Luftfeuchte 20°C neg. Korona
rel. Luftfeuchte 33% Raumtemperatur neg. Korona rel. Luftfeuchte 33% Raumtemperatur pos. Korona