Particle Formation in Premixed and Diffusion Flames · 2019. 12. 11. · Particle Formation in Premixed and Diffusion Flames Dr. Frank Ernst [email protected] phone: 044 632

Particle Formation in Premixed and Diffusion Flames

Dr. Frank Ernst

[email protected]

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

Diffusion flames

flame types

Particle formation in vapor-fed flames

Scale-up of diffusion flames

Particle morphology

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



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



50 mm HAB, r = 0 mm r = 3 mm r = 6 mm

r = 9 mm r = 12 mm r = 15 mm

200 nm

13

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

14

Diffusion flame Premixed flame

15

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

16

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

17

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

18

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…

19



CH4

Air

Air

TiCl4

CH4

CH4

CH4

Air Air

TiCl4

TiCl4

TiCl4

CFD flow fields

20

CH4

Air

Air

TiCl4

CH4

CH4

CH4

Air Air

TiCl4

TiCl4

TiCl4



21

Particle formation in vapor-fed flames

Gaseous

Precursor

Molecules

Nucleation

Primary

Particles

Coagulation

and Sintering

Agglomerated

Particles Non-Agglomerated

Particles

t

100nm

22

Methane

Air

Argon / TiCl4FIC

FIC

FIC

Argon

Methane

Air

TiCl4

Flame Reactor

Hood

Filter Assembly

Pump

NaOH Solution

Pratsinis, Zhu, Vemury, Powder Technology 86, 87-93 (1996)

Particle Morphology:

Set-up for SiO2/TiO2 production (lab scale)

23

Oxygen flow rate

Silica producing flame (17 g/h)

2.5 l/min 4.7 l/min 8.5 l/min 13.3 l/min 24 l/min

5 cm

Effect of oxidant flow on flame

Mueller R., Kammler H.K., Pratsinis S.E., Vital A., Beaucage G., Burtscher P., Powder Technol., 140, 40-48 (2004).

24

Particle Size Control by O2 flow

THMDSO: 5°C

N2 = 2.9 l/min

CH4 = 1.4 l/min

100

80

60

40

20

0

BE

T-e

qu

iva

len

t p

art

icle

dia

me

ter

[nm

]

2520151050

Oxygen flow rate [l/min]

Silica Production Rate 17 g/h


25

Particle Size Control by O2 flow

9 g/h 100

80

60

40

20

0

BE

T-e

qu

iva

len

t p

art

icle

dia

me

ter

[nm

]

2520151050

Oxygen flow rate [l/min]

Silica Production Rate

17 g/h

9 g/h

THMDSO: 5°C

Production rate 17 g/h:

• N2 = 2.9 l/min

• CH4 = 1.4 l/min

Production rate 9 g/h:

• N2 = 1.4 l/min

• CH4 = 0.7 l/min


26

Fourier transformed infrared spectrometer

t

Hood

Iris

Fourier transform infrared

(FTIR) spectrometer

IR

Detector

eFTIR

Detector

Y

X

Filter

Diffusion

Burner

30 mm

N2

O2

N2/HMDSO

CH4

Chimney


27

O2: 2.5 l/min

Conversion of Fuel Absorption Spectra 0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Ab

so

rba

nc

e

3000 2500 2000 1500 1000

Wavenumber [cm-1

]

no combustion

10 mm HAB

50 mm HAB

90 mm HAB

150 mm HAB

CO2

CH4, HMDSO CH4, HMDSO

HMDSO

SiO2

SiO2

100

75

50

25

0

Co

nv

ers

ion

of

CH 4 a

nd

HM

DS

O,

%

1007550250

Height above burner (HAB) [mm]

Oxygen2.5 l/min

Flame Characterization


28

2.5 l/min

Conversion of Fuel Axial Flame Temperature 100

75

50

25

0

Co

nv

ers

ion

of

CH 4 a

nd

HM

DS

O,

%

1007550250


Oxygen2.5 l/min

2500

2000

1500

1000

500

Av

era

ge

fla

me

te

mp

era

ture

[K

]

350300250200150100500


Oxygen2.5 l/min



29

17 g/h


75

50

25

0

Co

nv

ers

ion

of

CH 4 a

nd

HM

DS

O,

%

1007550250


Oxygen2.5 l/min

4.7 l/min

8.5 l/min

13.3 l/min

24 l/min

2500

2000

1500

1000

500

Av

era

ge

fla

me

te

mp

era

ture

[K

]

350300250200150100500


Oxygen2.5 l/min

4.7 l/min

8.5 l/min

13.3 l/min

24 l/min



30

17 g/h


75

50

25

0

Co

nv

ers

ion

of

CH 4 a

nd

HM

DS

O,

%

1007550250


Oxygen2.5 l/min

4.7 l/min

8.5 l/min

13.3 l/min

24 l/min

2500

2000

1500

1000

500

Av

era

ge

fla

me

te

mp

era

ture

[K

]

350300250200150100500


Oxygen2.5 l/min

4.7 l/min

8.5 l/min

13.3 l/min

24 l/min

2000 K

2250 K



31

Effect of O2 flow on Particle Size

2.5 l/min 4.7 l/min

8.5 l/min 13.3 l/min

24 l/min Degussa OX-

50

dBET = 44 nm

dBET = 55 nm

dBET = 78 nm

dBET = 41 nm

dBET = 23 nm dBET = 55 nm

17 g/h


32

Scale up:

Variation of Burner Geometry

5.6

4.1

2.8

Burner 1

5.7

7.6

10

Burner 2

6.0

12.0

27.0

Burner 3

Dimensions in mm

Wegner K., Pratsinis S.E., Chem. Eng. Sci. 58, 4581-4589 (2003).

33

Oxygen Flow Rate, L/min

0 2 4 6 8 10BE

T-e

qu

iva

len

t P

art

icle

Dia

me

ter,

nm

0

20

40

60

80

100

Control of Silica Primary Particle

Diameter by the O2 Flow Rate

Burner 1

34

Oxygen Flow Rate, L/min

0 10 20 30 40 50BE

T-e

qu

iva

len

t P

art

icle

Dia

me

ter,

nm

0

20

40

60

80

100

Burner 1

2

3

Conditions:

CH4: 0.5

L/min

Ar: 0.3 L/min

SiO2: 5 g/h

Separate Operation Lines for each Burner

35

Single Operation Line dp = f(Dv)

Dv = vOx

- vFuel

, m/s

0 5 10 15 20 25 30

BE

T -

equiv

ale

nt P

art

icle

Dia

mete

r, n

m

0

20

40

60

80

100

Burner 1

Silica

36


Dv = vOx

- vFuel

, m/s

0 5 10 15 20 25 30

BE

T -

equiv

ale

nt P

art

icle

Dia

mete

r, n

m

0

20

40

60

80

100

Burner 1

2

Silica

37


Dv = vOx

- vFuel

, m/s

0 5 10 15 20 25 30

BE

T -

equiv

ale

nt

Part

icle

Dia

mete

r, n

m

0

20

40

60

80

100

Burner 1

2

3

Silica

38

Dv = vOx

- vFuel

, m/s

0 5 10 15 20 25 30BE

T-e

qu

iva

lent P

art

icle

Dia

mete

r, n

m

0

20

40

60

80

100C-Flame

Operation Line for Silica synthesis

39

Dv = vOx

- vFuel

, m/s

0 5 10 15 20 25 30BE

T-e

quiv

ale

nt P

art

icle

Dia

mete

r, n

m

0

20

40

60

80

100C-Flame

Briesen et al., 1998


40

Dv = vOx

- vFuel

, m/s

0 5 10 15 20 25 30BE

T-e

quiv

ale

nt P

art

icle

Dia

mete

r, n

m

0

20

40

60

80

100C-Flame

Premixed Flame



0, premixed

41

Dv = vOx

- vFuel

, m/s

0 5 10 15 20 25 30BE

T-e

quiv

ale

nt

Part

icle

Dia

mete

r, n

m

0

20

40

60

80

100

D-Flame, Burner 1

C-Flame

D-Flame, Burner 2

Premixed Flame



0, premixed

42

Dv = vOx

- vFuel

, m/s

0 5 10 15 20 25 30BE

T-e

qu

iva

len

t P

art

icle

Dia

me

ter,

nm

0

20

40

60

80

100Methane

Propane

Hydrogen

Different Fuels – Same Flame Enthalpy 25 g/h SiO2, 38 kJ/min by variation of fuel flow rate

43

CH4

Air

Air

TiCl4

CH4

CH4

CH4

Air Air

TiCl4

TiCl4

TiCl4



44

Air

O2/N2

50/50

O2

Air CH 4

TiCl 4

Air

CH 4

TiCl 4

Flame

Mixing B

Flame

Mixing C

Zhu and Pratsinis, 1996

Effect of oxidant composition on TiO2

morphology

45

Degree of Agglomeration matters...

Agglomerated:

fillers

catalysts

lightguide performs

particles for chemical mechanical polishing (CMP)

catalysts

…

Non-Agglomerated:

pigments

composites (e.g. for dental applications)

electronics

…

46

Particle formation revisited

Particle growth in premixed flames: axial and radial effects

Diffusion flames: particle formation in co-flow flames

Morphology

Diffusion flame: Effects on particle size: dilution effect, residence time at

high T, precursor concentration

Scale-up: difference in gas velocities is decisive for particle size

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

47

Further reading

Chung S.-L., Katz J.L., The Counterflow Diffusion Flame Burner: A New Tool for the Study of the

Nucleation of Refractory Compounds. Combustion and Flame 61, 271-284 (1985).

Xing Y., Kole T.P., Katz J.L., Shape-controlled synthesis of iron oxide nanoparticles. J. Materials Science

Letters 22, 787-790 (2003).

Santoro R.J., Miller J.H., Soot Particle Formation in Laminar Diffusion Flames. Langmuir 3 (2), 244-259

(1987).

Pratsinis S.E., Zhu W., Vemury S., Teh role of gas mixing in flame synthesis of titania powder. Powder

Technol. 86, 87-93 (1996).

Mueller R., Kammler H.K., Pratsinis S.E., Vital A., Beaucage G., Burtscher P., Non-agglomerated dry

silica nanoparticles. Powder Technol. 140, 40-48 (2004).

Wegner K., Pratsinis S.E., Scale-up of nanoparticle synthesis in diffusion flame reactors. Chem. Eng.

Sci. 58, 4581-4589 (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).

Wegner K., Stark W.J., Pratsinis S.E., Flame-nozzle synthesis of nanoparticles with closely controlled

size, morphology and crystallinity. Materials Letters 55, 318 (2002).

Wegner K., Pratsinis S.E., Nozzle-quenching process for controlled flame synthesis of titania

nanoparticles. AIChE J. 49, 1667-1675 (2003).

Particle Formation in Premixed and Diffusion Flames · 2019. 12. 11. · Particle Formation in Premixed and Diffusion Flames Dr. Frank Ernst [email protected] phone: 044 632

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