Post on 18-Oct-2020
Centre for Research & Centre for Research & Technology Hellas (CERTH)Technology Hellas (CERTH)
Institute for Solid Fuels Technology & Applications (ISFTA)
64th ΙΕΑ
– FBC meeting. June 2012 Naples
Nikolopoulos A., Nikolopoulos N. Grammelis P., Kakaras Em.
Contact: +30 210 6501 510, Fax : +30
210 6501 598, E-mails:
a.nikolopoulos@certh.gr, grammelis@certh.gr
3-D CFD SIMULATION OF A CFB CARBONATOR COLD MODEL
Presentation overview
♦♦MotivationMotivation
♦♦CFD modelingCFD modeling
EMMSEMMS
Full loop Full loop simulationsimulation
ResultsResults
♦♦ConclusionsConclusions
Presentation overview
♦♦MotivationMotivation
♦♦CFD modelingCFD modeling
EMMSEMMS
Full loopFull loop
ResultsResults
♦♦ConclusionsConclusions
Calcium looping is an attractive post combustion CO2
capture technology especially for retrofitting power plants.
Motivation
CO2
650oC
900oC
ASUair
fuel
flue gasPower plantfuel
“clean” flue gas
O2
N2
carbon
ator
calciner
dryer
purge
F0
FR
FCO2
CaCO3
2 3CaO CO CaCO eat
3 2CaCO eat CaO CO
Carbonation
Calcination
The effectiveness of this process mainly relays on the design and operating parameters of the two interconnected Circulating Fluidized bed reactors (Carbonator -
Calciner). Especially,
carbonator is a novel reactor and there is no data available for
large scale. Proper comprehensive CFD modeling is important for design optimization.
Presentation overview
♦♦MotivationMotivation
♦♦CFD modelingCFD modeling
EMMSEMMS
Full loop simulationFull loop simulation
ResultsResults
♦♦ConclusionsConclusions
•
Isothermal CFD modeling of plexi-glass cold model (Carbonator) of USTUTT
•
Operating conditions received from USTUTT (PSD, TSI ≈
1.5 Kg, Superficial gas velocity 2.89 m/s).
•
3-D transient full full ––
loop loop (CFB loop) TFM CFD simulation of
the plexi –
glass CFB cold model.
•
Dense Grid applied (~287,000 cells287,000 cells, equivalent cell length to particle diameter ratio : ~ 21~ 21)
•
The EMMS scheme was applied for the hydrodynamic simulation of USTUTT’s CFB cold model isothermal flow.
•
For the returning system, a new stress model new stress model for the inter – particle friction forces was developed.
CFD modeling
Presentation overview
♦♦MotivationMotivation
♦♦CFD modelingCFD modeling
EMMSEMMS
Full loop simulationFull loop simulation
ResultsResults
♦♦ConclusionsConclusions
--
CERTH/ISFTA developed an advanced EMMS model for the CERTH/ISFTA developed an advanced EMMS model for the operating conditions of the plexi operating conditions of the plexi ––
glass carbonator cold model of glass carbonator cold model of
USTUTTUSTUTT
--
EMMS formulationCFD modeling
uf
upf
upfupf
upc
upc
upcuf
uc
usi
usi
g
Slip vel. definition
usf = uf ‐ upfusc = uc ‐ upc
upc
ucComputational domain
-
EMMS schemes. Dense
(clusters) and dilute
phase (dispersed particles) in each Control Volume (C.V.).
EMMS formulation
Particle Particle --
gas properties for USTUTT gas properties for USTUTT cold model testscold model tests
Particle Diameter 142 μm Particle Density 5700 kg/m3
Gas Density 1.225 kg/m3
Gas Viscosity 1.7894 10-5
kg/(ms)εmf 0.55
EMMS scheme is formulated incorporating:Mass and momentum conservation equations for (Dense
and dilute, C.V.)
Semi –
empirical equations (Clusters diameter and bulk density) Constraints
Objective function: Minimum energy
interexchange between gas and solids
- The governing equations(EMMS model) were obtained for the operating conditions of USTUTT cold
model, and solved for all possible combinations of voidagevoidage and uuslipslip prior to their CFD implementation
and numerical run.
-
The non-linear optimization EMMS problem was solved with GAMS software and the results were
integrated in Fluent package with C++ UDF (User Defined Functions) coding
CFD modeling
10
EMMS equations
1 11
min
st f f f c c c i i fg s
N m F U m F U m F U f
imum
= 1 1 1EMMS g c c f f s gF f g a f g a
,Wen Yud
Emms
FH
F
c g n 60.027 10 32cl p p s sd d d
13 3 14 4
cdc g sc sc di si si c s g c
p cl g
f fC U U C U U f g ad d
1 13 1 14
fdf g sf sf f s g f
p
fC U U f g a
d
1 11
f g g c gdf sf sf di si si dc sc sc
p cl p
fC U U C U U C U Ud f d d
1f c g gU f U f u 1 1pf pc s gU f U f u
1g c ff f
Semi –
empirical equations
Closure equations
Mass conservationMomentum conservation
Objective function
ResultsResults
CFD modeling
Dense phase Dilute Phase Inter-phase
Effective drag coef.
4.650dc d cC C
4.650df d f fC C
4.65(1 )Di DoiC C f
Standard drag coef. 0 0.313
24 3.6Re Red c
c c
C
0 0.313
24 3.6Re Red f
f f
C
0 0.313
24 3.6Re Red i
i i
C
Reynolds number Re g p
c scg
dU
Re g pf sf
g
dU
Re g cli si
g
dU
Slip velocity 1
c pcsc c
c
UU U
1
f pfsf f
f
UU U
11f pc
si fc
UU f U
Drag force 2
4 2p g
c dc sc sc
dF C U U
2
4 2p g
f df sf sf
dF C U U
2
4 2gcl
i di si sidF C U U
Numbers of particles or clusters
3
1
6
cc
p
fm
d
3
1 1
6
ff
p
fm
d
3
6
icl
fmd
EMMS formulation
020406080
100120140160180200
0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1
Hd (‐)
εg (‐)
Heterogeneity indexThe Hd
(εg
) function for uslip
=2 m/sec.
- 18
interpolation polynomials
for slip velocity: 0.25, 0.5, 0.75, 1, 1.25 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 4, 5, 6, 8
| |,d slip gH f u
•
The results (Hd
index) of the optimization problem, were interpolated in order to be efficiently introduced in the Fluent
CFD
package (via UDF).FEMMS
= FWen,Yu / Hd
CFD modeling
Presentation overview
♦♦MotivationMotivation
♦♦CFD modelingCFD modeling
EMMSEMMS
Full loop simulationFull loop simulation
ResultsResults
♦♦ConclusionsConclusions
13
Inter-particle frictional forces
“Dilute”
flow (εs
< 0.5)
“Dilute”
flow Kinetic theory (Gidaspow)
“Dense”
flow (εs
> 0.5)
“Dense”
flow
Plastic theory
(Drucker -
Prager)
In the CFBs recirculation system the flow is dense and inter –
particle
friction forces prevail.
CFB flow is simulated with the Euler –
Euler (TFM) approach
Solids are considered as a “Pseudo”-
fluid
Full loop simulation
14
Yield criterion(Tresca, von Mises, Drucker-Prager, Gray –Stiles)
Flow ruleassociated flow rule Drucker-Prager
Plastic theory
Model development / State-of-the-art
The rate of energy loss during plastic deformation is zero
(W = Di σi = 0)
Εxtended von Mises, Drucker-Prager
Only dilatancy and NOT consolidation in a control volume is properly modeled
22sin 0dTY II
Full loop simulation
15
InterInter--particle frictional forcesparticle frictional forces
Yield criterion:
Pitman - Schaeffer - Gray – Stiles Critical point
The rate of energy loss rate of energy loss during plastic deformation during plastic deformation
is not zerois not zero(W = Di σi ≥
0)
Both dilatancy and consolidation in a control volume are properly modeled
Disadvantage: Numerical stiffness
sP u
Model development / new model
16
Constitutive equationsConstitutive equations
Conventional model
New model
TFM equations Stress ModelStress Model
InterInter--particle frictional forcesparticle frictional forces
210 4[1 (1 )]96 (1 ) 5
s s so s ss
s ss o
dg e
e g
s o ss sss ss
s o ss ss
g
ss o s s ss ss
5 2 1 3 124 1 3
451
6 1 3 1
g e edg e e
g d e e
s
s s o ss ss
4 15
king e d
sin
2fr
s dD
PII
2
2 2s
sin4sin ( )
s
dD s
Pu
2 24sin ( )s
s dD s
P
II u
kin
col ss s s o ss
4 (1 )5
d g e
fr
fr 0
μsshear
frs s kin col
frs s kin col fr
kin col fr
μsbulk
frs s kin
frs s fr
frs s kin
frs s fr
sP fr
s s kinfr
s s fr
P
P
frs s kin
frs s kin fr
P
P P
og11
3s
maxs
1
max2.5
smaxs
1s
17
InterInter--particle frictional forcesparticle frictional forces
Model validation through 2D CFD Model validation through 2D CFD simulation of a repose angle simulation of a repose angle ((φφexpexp
=36.03=36.03oo) measurement experiment ) measurement experiment (Geldart B)(Geldart B)
The new model through appropriate The new model through appropriate UDFs was implemented in Fluent 13 UDFs was implemented in Fluent 13
Transient simulation: Transient simulation: ΔΔT = 40T = 40μμss
φφexpexp
=3=366..0303οο
Batch of particles at T=0sBatch of particles at T=0s
Free fallFree fall
Two CFD models were applied: Two CFD models were applied: --
Conventional oneConventional one(Ext. von Mises)(Ext. von Mises)
--
New oneNew one(Pitman (Pitman --
Schaeffer Schaeffer --
Gray Gray ––
Stiles)Stiles)
Stress Model ValidationStress Model Validation
18
InterInter--particle frictional forcesparticle frictional forcesC
onve
ntio
nal m
odel
Con
vent
iona
l mod
elN
ew m
odel
New
mod
el 1.2 sec1.2 sec 2.2 sec2.2 sec1.8 sec1.8 sec
φφexpexp
=3=366..0303οοStress Model ValidationStress Model Validation
1.1 sec1.1 sec 1.4 sec1.4 sec 1.82 sec1.82 sec
t 1.20 sec
φφ==2121οο
φφ<4<4οο
Presentation overview
♦♦MotivationMotivation
♦♦CFD modelingCFD modeling
EMMSEMMS
Full loop simulationFull loop simulation
ResultsResults
♦♦ConclusionsConclusions
20
New stress model developed for the inter particle New stress model developed for the inter particle friction forces in the recirculation systemfriction forces in the recirculation system
CFB riser Loop - Seal
TFM equations Stress ModelStress Model
CFD simulation
continuity equations
momentum equations
Viscous Stress tensors
granular temperature
0
0
g g g g g
s s s s s
ut
ut
g g g g g g g
g g g g s g
s s s s s s s
s s s s s g s
u u ut
p g u u
u u ut
p p g u u
23
23
T
g g g g g g g g g
T
s s s s s s s s s
u u u I
u u u I
: 3 0ss s s sp I u
kin 210 4[1 (1 )]
96 (1 ) 5s s s
o s sss ss o
dg e
e g
s o ss sss ss
s o ss ss
g
ss o s s ss ss
5 2 1 3 124 1 3
451
6 1 3 1
kin
g e edg e e
g d e e
col 4 (1 )5
ss s s o ssd g e
4 (1 ) /5
ss s o ss kin s sg e d
fr sin
2fr
s dD
P
II
2
22
sin
4sin
fr
s dD s
P
II u
fr 0 224sin
fr
s dD s
P
II u
og 11
3
max1 s
s
max2.5
max1s
s
s
- The CFD model developed incorporates the EMMS scheme and the new stress model for the recirculation system.
21
-
The EMMS scheme developed increases the accuracy of the model especially in the
dense bottom region which is hard to model, and in which the majority of CO2
capture takes place.
CFD modeling of plexiCFD modeling of plexi--glass cold model (glass cold model (CarbonatorCarbonator) of USTUTT) of USTUTT
CFD simulation
22
The model incorporating the EMMS scheme efficiently captures the hydrodynamics of the CFB carbonator with high accuracy.
Regarding Pressure profile the mean error is less than 10%.
The error in the re-circulation flux is less than 2% depicting the sophistication of the developed models for the inter-particle friction forces.
CFD simulation
23
CFD simulationContours of time averaged volume fraction of solidsContours of time averaged volume fraction of solids
Riser exit -
cyclone
Bottom zone
Loop Seal
24
CFD simulationVectors of time averaged solids velocityVectors of time averaged solids velocity
Bottom zoneLoop Seal
Presentation overview
♦♦MotivationMotivation
♦♦CFD modelingCFD modeling
EMMSEMMS
Full loop simulationFull loop simulation
ResultsResults
♦♦ConclusionsConclusions
•
The developed EMMS scheme along with the implementation of a dense grid resulted in highly accurate results with respect to the governing hydrodynamics of the CFB cold model carbonator.
•
In full loop simulations of CFBs the inter –
particle friction forces should be accurately simulated. The stress tensor formulation based on the
von-
Mises
yield criterion severely under –
predicts the friction forces.
•
The developed stress tensor formulation based on Pitman - Schaeffer - Gray – Stiles Yield criterion efficiently captures the hydrodynamic behavior of the Loop –
Seal.
Conclusions
27
CERTH/ISFTA
Thank you for your attention!
Questions?
Acknowledgements: The present work was funded by the Research Programme of the Research Fund for Coal and Steel Coal RTD (Research Project CaL –
Mod
/ RFCS-CT-2010-0013