Euler-Euler and Euler-Lagrange Modeling of Wood ... · Euler-Euler and Euler-Lagrange Modeling of...
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Euler-Euler and Euler-Lagrange Modeling of
Wood Gasification in Fluidized Beds
Michael Oevermann Stephan Gerber Frank Behrendt
Berlin Institute of Technology
Faculty III: School of Process Sciences and Engineering
Department of Energy Engineering
Chair for Energy Process Engineering and Conversion Technologies for
Renewable Energies
Fasanenstr. 89, 10623 Berlin, Germany
CFB-9, May 13-16, 2008, Hamburg
Overview
Motivation
Modeling approaches
Euler-Lagrange / Discrete Element Method (DEM)
Euler-Euler
Results
Summary and outlook
Motivation - simulation of wood gasification
Renewed interest in producing gas from biomass
Gasification in fluidized bed reactors
Lack of detailed knowledge about the complex interactions
between heterogeneous reactions and the fluid mechanics
in fluidized beds
Develop closure laws for large scale models
CFD modeling for particulate flow
Continuum models Euler-Lagrange DNS
tractable problem size
computational cost
Euler-Lagrange model
Basis:
OpenFOAM (www.opencfd.co.uk/openfoam)
Modules:
1 Solver for the gasphase (OpenFoam)
2 Lagrangian particle tracking / DEM (OpenFOAM)
3 Particle combustion / gasification model
(here: simple zero dimensional particle model)
Euler-Lagrange model – gasphase
Mass / momentum balance:
(ρε)t +∇ · ερu = ερs
(ερu)t +∇ · {ερuu}+∇p −∇ · τ + ερg = Fs
Energy / species balance:
(ρεE)t +∇ · [(ρE + p)εu] +∇ · q = Qs
(ρεuYα)t +∇ · [ρεYαu]− εwα = ερα,s
ρs, Qs, ρα,s
Euler-Lagrange model – particle tracking
Equation of motion for every single particle
mid~vi
dt+ ~vi
dmi
dt=
∑j
~Fij
Jid~ω
dt+ ~ω
dJi
dt=
∑j
~Mij
Fluid dynamic forces ( drag, buoyant, Magnus, etc.) withempirical correlations
Contact forces via spring-damper modell
Multiple particle contacts possible
Euler-Lagrange – contact forces by DEM
(Cundall & Strack, 1979)
i jkn
ηn µt
ktηt
~F nij = knδ~n + ηn~vn
ij
~F tij = min
(µt |~F n
ij |~t , ηt |~v tij |
)
Euler-Lagrange model – coupling
Detailed single particle
(Eulerian)
Solid phase
Qp,m
p s
Rp, m
ρg,~ v
g,~ω
g,T
g
~ Fs ,
Qsi,ε
(e. g. T p, Y ps )
φ
(Lagrangian)
iner
tre
actin
g
~r si(t), ~vsi(t)
~ωpi(t),T si(t),Qsi
~r sr(t), ~vsr(t)
~ωpr(t)
model (1d)Rp(t), mp(t), T p(t)
mps(t), Qp(t)
Particle library
mps(t ; φ), Qp(t ; φ)
Rp(t ; φ), mp(t), T p(t ; φ)
ρg(~x , t), ~vg(~x , t)
T g(~x , t), Y gs (~x , t)
Gas phase
Euler-Euler model
Public Domain Code MFIX (www.mfix.org)
1 gas phase
3 solid phases: wood (4mm), 2 x charcoal (1mm, 2mm)
5 homogeneous gas phase reactions (rev.),
4 heterogeneous reactions carbon
Models for primary and secondary pyrolysis
Gas phase chemistry
Simple reaction mechanism
Species: H2, O2, N2, CO, CO2, CH4, H2O, tar
1. 2 CO + O2 2 CO2
2. 2 H2 + O2 2 H2O
3. 2 CH4 + 3 O2 2 CO + 4 H2O
4. CO + H2O H2 + CO2
5. CH4 + H2O CO + 3 H2
Pyrolysis / heterogeneous reactions
Primary pyrolysis (Grönli, Melan (2000))
wood → H2O(g), CO(g), CO2(g), H2(g), CH4(g), tar(g), char(s).
Secondary pyrolysis (Boroson et al. (1989))
tar → CO(g), CO2(g), H2(g), CH4(g), tarinert.
Heterogeneous reactionsC + O2 → CO2 (Ross and Davidson(1982))
C + CO2 → 2 CO (Biggs and Agarwal(1997))
C + H2O → CO + H2 (Hobbs et al. (1992))
C + 2 H2 → CH4 (Hobbs et al. (1992))
Reactor at the department
Holzdosierung
Holzzufuhr
Reaktor
Gasfilter
Gasbrenner
Ø 95
42
60
0
110
0
Ø 5
0
50
Ø134
fuel inlet
air
productgasoutlet
Reactor at the department
Reactor – inlet boundaries
Ø 95
42
60
0
110
0
Ø 5
0
50
Ø134
fuel inlet
air
productgasoutlet wood inflow:
wood T = 150 ◦C, v = 0.08 cm/s
bulk density 0.385 g/cm3
air inflow:
gas species 21% O2, 79% N2
T = 400 ◦C, v = 25 cm/s
Results - Euler-Euler model
play play
Results – exhaust gas composition
Tar
H2O
CH4
CO
CO2
Time / s
Results - Euler-Euler model
0
0,05
0,1
0,15
0,2
0,25
E1 E2 E3 E4 E5 E6 E7 E8 E9 E10E11
E12E13
E14E15
E16E17
S1 S2
Vol % hydrogen carbon monoxidecarbon dioxide hydrocarbons
Experiments Simulations
Euler-Lagrange / DEM – results
Model assumptions:
proportional particle massloss and shrinking
transient calculation of particle mass-loss and energy
no heterogeneous reaction (in progress)
no particle-particle heat transfer
no radiation
Euler-Lagrange / DEM – results
play play
Summary and outlook
Euler-Lagrange and Euler-Euler model for woodgasification in fluidized beds
Euler-Euler: reasonable agreement with experimental data
Euler-Lagrange: allows detailed investigation ofparticle/chemistry/gas phase interactions
Refined chemistry
Parallelization of the DEM modell
Quantitative comparison between Euler-Euler,Euler-Lagrange/DEM und experiments
Coupling Euler-Lagrange with Euler-Euler methods
The financial support of the
Deutsche Bundesstiftung Umwelt (DBU)
is gratefully acknowledged!
Governing equations – Euler-Euler model
Species mass balance gas phase
∂
∂t(εgρgYgs) +∇ · (εgρg~vgYgs) = ∇ · (Dgs∇Ygs) + Rgs
Mass balance solid phase
∂
∂t(εmρmYms) +∇ · (εmρm~vsmYms) = ∇ · (Dms∇Yms) + Rms
Governing equations – Euler-Euler model
Momentum balance solid phase
∂
∂t(εmρm~vm)+∇·(εmρm~vm~vm) = −εm∇pm+∇·τm−
nm∑l=1l 6=m
~Iml +~Igm+εmρm~g
Governing equations – Euler-Euler model
Energy balance gas phase
εgρgcpg
(∂Tg
∂t+ ~vg · ∇Tg
)= −∇ · ~qg +
Nm∑m=1
γgm(Tm − Tg
)−∆Hg
Energy balance solid phases
εmρmcpm
(∂Tm
∂t+ ~vm · ∇Tm
)= −∇ · ~qm − γgm
(Tm − Tg
)−∆Hm