particle formation in premixed and diffusion flames...particle formation in premixed and diffusion...

Particle Formation in Premixed and Diffusion Flames

Dr. Frank Ernst

ernst@ptl.mavt.ethz.ch

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