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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

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Overview

Motivation

Modeling approaches

Euler-Lagrange / Discrete Element Method (DEM)

Euler-Euler

Results

Summary and outlook

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Motivation - simulation of wood gasification

Renewed interest in producing gas from biomass

Gasification in fluidized bed reactorsLack of detailed knowledge about the complex interactions

between heterogeneous reactions and the fluid mechanics

in fluidized beds

Develop closure laws for large scale models

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CFD modeling for particulate flow

Continuum models Euler-Lagrange DNS

tractable problem size

computational cost

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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)

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Euler-Lagrange model gasphase

Mass / momentum balance:

()t + u = s

(u)t + {uu} + p + g = Fs

Energy / species balance:

(E)t + [(E + p)u] + q = Qs

(uY)t + [Yu] w = ,s

s, Qs, ,s

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Euler-Lagrange model particle tracking

Equation of motion for every single particle

midvidt

+ vidmidt

=

j

Fij

Jid

dt+

dJidt

=

j

Mij

Fluid dynamic forces ( drag, buoyant, Magnus, etc.) with

empirical correlations

Contact forces via spring-damper modell

Multiple particle contacts possible

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Euler-Lagrange contact forces by DEM

(Cundall & Strack, 1979)

i j

kn

n t

kt

t

Fnij = knn+ nvnij

Ftij = min

t|Fnij |

t, t|vtij|

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Euler-Lagrange model coupling

Detailed single particle

(Eulerian)

Solid phaseQp,

mp s

Rp, m

g,

vg,

g,

Tg

Fs,

Qsi ,

(e. g. Tp,Yp

s )

(Lagrangian)

inert

reacting

r

si

(t),v

si

(t)pi(t),Tsi(t),Qsi

rsr(t), vsr(t)

pr(t)

model (1d)

Rp(t),mp(t), Tp(t)

mps(t), Q

p(t)

Particle library

mps(t;), Q

p(t;)

Rp(t;), mp(t), Tp(t;)

g(x, t), vg(x, t)

Tg(x, t),Yg

s(x, t)

Gas phase

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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

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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

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Pyrolysis / heterogeneous reactions

Primary pyrolysis (Grnli, 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 reactions

C + 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))

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Reactor at the department

Holzdosierung

Holzzufuhr

Reaktor

Gasfilter

Gasbrenner

95

42

600

1100

5

0

50

134

fuelinlet

air

productgasoutlet

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Reactor at the department

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Reactor inlet boundaries

95

42

600

110

0

5

0

5

0

134

fuelinlet

air

productgasoutlet wood inflow:

wood T = 150 C, v = 0.08 cm/s

bulk density 0.385 g/cm

3

air inflow:

gas species 21% O2, 79% N2

T = 400 C, v = 25 cm/s

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Results - Euler-Euler model

play play

http://pdf/mfixsimu1.mpghttp://pdf/mfixsimu2.mpghttp://pdf/mfixsimu2.mpghttp://pdf/mfixsimu1.mpghttp://find/http://goback/

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Results exhaust gas composition

Tar

H2O

CH4

CO

CO2

Time / s

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Results - Euler-Euler model

0

0,05

0,1

0,15

0,2

0,25

E1 E2 E3 E4 E5 E6 E7 E8 E9E10

E11E12

E13E14

E15E16

E17S1 S2

Vol % hydrogen carbon monoxidecarbon dioxide hydrocarbons

Experiments Simulations

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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

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Euler-Lagrange / DEM results

play play

http://pdf/cfbmoviemittwoch.mpghttp://pdf/cfbmoviedonnerstag.mpghttp://pdf/cfbmoviedonnerstag.mpghttp://pdf/cfbmoviemittwoch.mpghttp://find/http://goback/

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Summary and outlook

Euler-Lagrange and Euler-Euler model for wood

gasification 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 modellQuantitative comparison between Euler-Euler,

Euler-Lagrange/DEM und experiments

Coupling Euler-Lagrange with Euler-Euler methods

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The financial support of the

Deutsche Bundesstiftung Umwelt (DBU)

is gratefully acknowledged!

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Governing equations Euler-Euler model

Species mass balance gas phase

t

(ggYgs) + (ggvgYgs) = (DgsYgs) + Rgs

Mass balance solid phase

t

(mmYms) + (mmvsmYms) = (DmsYms) + Rms

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Governing equations Euler-Euler model

Momentum balance solid phase

t(mmvm)+(mmvmvm) = mpm+m

nml=1l=m

Iml+Igm+mmg

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Governing equations Euler-Euler model

Energy balance gas phase

ggcpgTgt

+ vg Tg = qg +Nm

m=1

gmTm Tg Hg

Energy balance solid phases

mmcpmTm

t

+ vm Tm = qm gmTm Tg Hm

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