Particle Formation in Premixed and Diffusion Flames
Dr. Frank Ernst
phone: 044 632 25 10
Office hour:
Thursdays after the lecture
Department of Mechanical and Process Engineering
ETH Zurich, www.ptl.ethz.ch
Verbrennung und chemisch reaktive Prozesse in der Energie- und Materialtechnik
2
Particle formation revisited
Pre-mixed flames
particle formation
diagnostics
Electric field assisted particle formation
Diffusion flames
flame types
Particle formation in vapor-fed flames
Lecture outline
3
Particle formation & growth – key steps
Chemical reaction
Source of
monomer
species
Nucleation
Formation of clusters
Aggregation
Spherical particles form
via particle-particle
collisions
Collisions between
spherical particles form
chains
Coagulation
TiO2 TiCl4 + 2O2 TiO2 + Cl2
Decreasing number concentration
Increasing size and mass
4
TiCl4
TiCl4
TiCl4 H2
H2 H2 O2
O2 O2
TiO2
TiO2
TiO2 TiO2
H2O
H2O H2O
HCl
HCl
Chemical reaction
Nucleation
Aggregation
Coagulation
T (K)
25
00
20
00
15
00
10
00
50
0 Particle formation & growth – in flames
5
Premixed flames
Simple construction but particle
formation in these flames is
narrowly controlled.
Safety is an issue.
Excellent for basic
understanding and for
manufacture of a specific
product day in and day out.
Chemical reactions kinetics & thermodynamics
Fluid flow Laminar & turbulent
Temperature Particle
dynamics
6
Monitoring particle dynamics
by intrusive thermophoretic sampling
Burner
TI
t
Hood
Filter
Iris
X
Y
Fourier transform
infrared (FTIR) spectrometer
IR
CH 4 , O 2 , N 2
HMDSO in N 2
Shield N 2
Detector
e FTIR
Detector
N 2
Control
box
7
TEM
grid
5 bar N2 pressure
tres = 50 ms
Thermophoretic particle sampler (original design by Dobbins and Megaridis, 1987)
8
Image Analysis
TEM
Particle size analysis in the flame
Thermophoretic Sampling
(Height: 33 mm)
0
10
20
30
40
50
60
0 1 2 3 4
Distance from the burner, cm
Av
era
ge
pri
ma
ry p
art
icle
dia
me
ter,
nm
.
TiO2 data by thermophoretic
sampling
42 ± 11 nm
9
Sampling position
Burner
TI
Hood
Filter
X
Y CH 4 , O 2 , N 2
HMDSO in N 2
Shield N 2
N 2
Control
box
10
TiO2
.5 mm 23 mm
Filter
-8 mm
200 nm
Kammler et al. (2001) Chem.
Eng. Technol. 24, 83.
13 mm
40 mm
55 mm
11
SiO2
Kammler et al. (2001) Chem.
Eng. Technol. 24, 83.
5 mm HAB
200 nm
10 mm HAB
20 mm HAB
30 mm HAB
40 mm HAB
50 mm HAB
70 mm HAB
90 mm HAB
110 mm HAB
150 mm HAB
Filter
200 nm
130 mm HAB
12
SiO2
Kammler et al. (2001) Chem.
Eng. Technol. 24, 83.
50 mm HAB, r = 0 mm r = 3 mm r = 6 mm
r = 9 mm r = 12 mm r = 15 mm
200 nm
13
Kammler, PhD thesis, ETH #14622 (2002)
U.S. Patent
5,861,132
(1999)
Vemury et al. (1997) J. Mater. Res. 12, 1031.
Electrically assisted synthesis of
nanoparticles
14
0.5 cm
5 cm
10 cm
no electric field
200 nm
Filter
20 cm
Evolution of
TiO2 particle
growth
200 nm
2 cm
0 kV/cm 2 kV/cm
HAB
HA
B
0.5 cm
5 cm
10 cm
Filter
20 cm
HAB with electric field
Kammler et al. (2003) Powder Technol. 135, 310.
15
Diffusion flames
Simple construction but
particle formation in these
flames is a complex
system
Requires detailed
understanding of key
processes and their
interaction
Chemical reactions kinetics & thermodynamics
Fluid flow Laminar & turbulent
Temperature Particle
dynamics
16
Diffusion flame Premixed flame
17
Diffusion flame
Turbulent diffusion flames are frequently
used in industry
Safety
Fuel and oxygen do not mix until furnace
Scale up
Up to several tonnes per hour
Simplicity
Flexibility in controlling product particle
characteristics
18
Chung S-L., Katz J.L., Combustion and Flame 61, 271-284 (1985).
Counter-flow Diffusion Flames
19
Counter-flow Diffusion Flames
20
Xing Y., Kole T.P., Katz J.L., J. Materials Science Letters 22 (2003).
http://www.engr.uconn.edu/~renfro/facilities.html
Counter-flow diffusion flames
21
Co-flow diffusion flames
Simplicity
Safe
Concentric pipes
Fuel, air and precursor in
each pipe CH4
Air
Air
TiCl4
CH4
CH4
CH4
Air Air
TiCl4
TiCl4
TiCl4
22
Materials made in vapor-fed flames
Product
Particles
Carbon black
Titania
Fumed Silica
Volume
t/y
8 M
2 M
0.2 M
Ind.Process
(dominant)
Vapor Flame
Vapor Flame
Vapor Flame
Use
(exemplary)
Inks, Rubber
Paints
Toothpaste, Tires
Chemical Economics Handbook, 2001; direct industrial quotes
• A wide range of interesting applications
• Significantly large commercial markets
23
Wolfhard-Parker slot burner: 2-D flame
Combustion of hydrocarbons
Santoro R.J., Miller J.H., Langmuir 3 (2), 244-259 (1987).
24
Santoro R.J., Miller J.H., Langmuir 3 (2), 244-259 (1987).
Radial Distribution of Gaseous Species
Concentrations
Hydrocarbon Combustion in
a Diffusion Flame
Measurement by Mass
Spectrometry
9 mm above the burner
25
Santoro R.J., Miller J.H., Langmuir 3 (2), 244-259 (1987).
Radial distribution of the velocities
Laser velocimetry
with parallel beams
and Al-Oxide
particle seeds
26
Radial Temperature Distribution along the
Diffusion Flame Axis (co-annular burner)
thermocouple
measurements
Santoro R.J., Miller J.H., Langmuir 3 (2), 244-259 (1987).
27
Axial Evolution of Radial Distribution of
Light-scattered by Soot along a Diffusion
Flame
Santoro R.J., Miller J.H., Langmuir 3 (2), 244-259 (1987).
28
Pratsinis, Zhu, Vemury, Powder Technol. 86, 87-93 (1996)
Johannessen, Pratsinis, Livberg, ibid., 118, 242-250 (2001).
CH4
Air
Air
TiCl4
CH4
CH4
CH4
Air Air
TiCl4
TiCl4
TiCl4
A few possible configurations…
29
Pratsinis, Zhu, Vemury, Powder Technol. 86, 87-93 (1996)
Johannessen, Pratsinis, Livberg, ibid., 118, 242-250 (2001).
CH4
Air
Air
TiCl4
CH4
CH4
CH4
Air Air
TiCl4
TiCl4
TiCl4
CFD flow fields
30
CH4
Air
Air
TiCl4
CH4
CH4
CH4
Air Air
TiCl4
TiCl4
TiCl4
Pratsinis, Zhu, Vemury, Powder Technol. 86, 87-93 (1996)
Johannessen, Pratsinis, Livberg, ibid., 118, 242-250 (2001).
31
Particle formation in vapor-fed flames
Gaseous
Precursor
Molecules
Nucleation
Primary
Particles
Coagulation
and Sintering
Agglomerated
Particles Non-Agglomerated
Particles
t
100nm
32
Particle formation revisited
Particle growth in premixed flames
axial and radial effects
electrical field effects
Diffusion flames
Counter-flow and co-flow flames
Species distribution
Further reading
Kammler H.K., Mädler L., Pratsinis S.E. Flame synthesis of nanoparticles. Chemical Engineering
Technology 24, 6 (2001).
Kammler H.K., Jossen R., Morrison P.W., Pratsinis S.E., Beaucage G. The effect of external electric
fields during flame synthesis of titania. Powder Technology 135-136, 310-320 (2003).
Pratsinis S.E., Zhu W., Vemury S. The role of gas mixing in flame synthesis of titania powders. Powder
Technology 86, 97-93 (1996).
Johannessen T., Pratsinis S.E., Livbjerg H. Computational analysis of coagulation and coalescence in
the flame synthesis of titania particles. Powder Technology 118, 242-250 (2001).
Lecture summary
