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Aerosol and Particle Transport in Biomass Furnaces
Erik van KemenadeEindhoven University of Technology
Thermo Fluids Engineering
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Background
Two Phase FlowTurbulence modellingPhase SeparationHeat Exchangers
BIOAEROSOLS
Graz University of TechnologyÅbo Akademi UniversityTechnical University of DenmarkERC GmbHMAWERA GmbHStandardKessel GmbH
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Contents
Applicability of CFD codes
Particle deposition
K-εLESDNS
MechanismsDiffusional deposition regimeInertia moderated regime
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fuel
flue gas
first boiler passage:43 tubes Ø53 x 2400
second boiler passage:24 tubes Ø53 x 31600
1500 Nm-3
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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
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0 100 200 300 400 599 600 700t+
1
2
3
4
cwall
DNSLES a prioriLES no inverseLES inverse
τp = 5.4
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•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
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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
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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
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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
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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
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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
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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