Aerosol and Particle Transport in Biomass Furnaces

Erik van KemenadeEindhoven University of Technology

Thermo Fluids Engineering

Background

Two Phase FlowTurbulence modellingPhase SeparationHeat Exchangers

BIOAEROSOLS

Graz University of TechnologyÅbo Akademi UniversityTechnical University of DenmarkERC GmbHMAWERA GmbHStandardKessel GmbH

Contents

Applicability of CFD codes

Particle deposition

K-εLESDNS

MechanismsDiffusional deposition regimeInertia moderated regime

fuel

flue gas

first boiler passage:43 tubes Ø53 x 2400

second boiler passage:24 tubes Ø53 x 31600

1500 Nm-3

0

0.01

0.02

0.03

0.04

0.05

0 0.5 1 1.5 2tube length [m]

tube

hei

ght[m

]

k-ε

0

0.01

0.02

0.03

0.04

0.05

0 0.5 1 1.5 2tube length [m]

tube

hei

ght[m

]

low k-ε

0

0.01

0.02

0.03

0.04

0.05

0 0.5 1 1.5 2tube length [m]

tube

hei

ght[m

]

low k-ω

0

4.102

8.102

1.2.103

1.6.103

0 0.005 0.01 0.015 0.02y [m]

turb

ulen

ce e

nerg

y di

ssip

atio

n

k-ε modellow k-ε modellow k-ω model

0 100 200 300 400 599 600 700t+

1

2

3

4

cwall

DNSLES a prioriLES no inverseLES inverse

τp = 5.4

•commercial CFD models are less suitable for describing particle behaviour

•inaccurate near wall

•geometrically inflexible

•computing time required

•use “global” methods to describe the main characteristics of the flow

•commercial CFD code

•Reynolds - Nusselt correlations (computerised)

•potential flow models

•add “blocks” for potential danger area’s

•tube (bundle)

•corners

•entrainment

Coarse Particles

0.5 0.4 0.3 0.2 0.1 0 0.1 0.2 0.3 0.40.4

0.3

0.2

0.1

0

0.1

0.2

0.3

0.4

x [m]

y [m

]

Um =5 m/s

dp =0.0001 mT =1000 ˚C

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

1 10 100 1000

aerodynamic particle diameter [µm]

F [-

]

a = 2000 kg m-3

1000

500

500

400

300

200

100

0

dmd log(dp)

[mg Nm-3 ]

10-8 10-7 10-6 10-5 10-4 10-3

dp [m]

0

0.2

0.4

0.6

0.8

1

F[-]

p = 2000 kgm-3

500

1000

eddy impactation

How do small particles reach the wall ?

Deposition velocity very close to the wall (viscous sublayer) :

++−−+ +⋅+== thd

d uuu

u243/2

* 105.4057.0 τSc

Brownian motion /eddy diffusion

thermophoresis

10-15

10-13

10-11

10-09

10-07

10-05

10-03

0 1 2 3 4 5 6

dp = 10 µmρp = 1000 kgm-3kp = 1 Wm-1K-1

length [m]

ud uth0.057 Sc-2/3u*

4.5.10-4.τ+2u*

first boilerpassage

second boilerpassage

depo

sitio

n ve

loci

ty [m

s-1 ]

0 1 2 3 4 5 6length [m]

first boilerpassage

second boilerpassage

depo

sitio

n ve

loci

ty [m

s-1]

ρp = 1000 kgm-3kp = 1 Wm-1K-1

dp = 10 µm

1 µm0.1 µm

0.4.10-5

0

0.8.10-5

1.2.10-5

1.8.10-5

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4

position [m]

rela

tive

conc

entr

atio

n [-]

n 0 = 1010 [m -3]

x 0 = 10-4 [m ol kg-1] 1011

1012

>1013

0.00E+00

2.00E-07

4.00E-07

6.00E-07

8.00E-07

1.00E-06

1.20E-06

0 1 2 3 4

position [m]

part

icle

siz

e [ µ

m]

n 0 = 1010 [m -3]

x 0 = 10-4 [m ol kg-1]1011

1012

1013

1014

Conclusions

• Description of the behaviour of large particles = OK

• The amount of small particles deposited is negligible

• Wall condensation can be of importance

• Integration of CFD and AFB models is essential regarding the boundary layer