"Post-combustion CO2 capture by Ca-looping"
Borja Arias RozadaCO2 Capture Group
National Institute of Coal (INCAR-CSIC)
Workshop on Mathematical Modelling of Combustion
23-25 May, Santiago de Compostela, Spain
Post-combustion CO2 capture using Ca-looping
• What is Ca-looping?• Ca-looping for post-combustion CO2 capture: description of the process• Status of the technology
• Modelling work:• Particle models• Reactor models
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
0,001
0,010
0,10
1,00
10,00
100,0
600 700 800 900 1000 1100
Carbonation
CalcinationCaO + CO2 CaCO3
Lime
CO2 capture
Gas with CO2
Sorbent regeneration
Sorbent+CO2CO2
Fresh sorbent
Sorbent
Spent sorbent
Energy
CO2 capture using solid sorbents
What is a Ca-looping?
Use of lime as sorbent
LimestoneP C
O2
eq, a
tm
Temperature (ºC)
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Advantages of Ca-looping versus other post-combustion technologies
CARBONATORCOMBUSTOR
Concentrated CO2
CoalCaCO3(F0)
CaO Purge
CaCO3
CaOFlue Gas
Flue gas“without” CO2
Coal Air
O2
Air
N2
ASU
CALCINER
Power OUT
Power OUT
CO2
Some advantages of Ca-looping:• Low energy penalty
• Purge of CaO: synergies with cement industry
• Pre-treatment of flue gas no needed Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Technical development of Ca-looping
• Classification of CO2 capture technologies:• Near commercial (amines, oxy-fuel combustion, pre-combustion)• Emerging technologies
Roadmap proposed for the development post-combustion CO2 capture with Ca-looping
Post-combustion CO2 capture using Ca-looping
• What is Ca-looping?• Ca-looping for post-combustion CO2 capture: description of the process• Status of the technology
• Modelling needs:• Particle models• Reactor models
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
EXPERIMENTAL
MODELLING
Particle models OD/1D Models 2D/3D Models
Post-combustion CO2 capture using carbonate looping
Lab ScaleSmall pilot plant scale
Pilot plant scale (1.7 MWt) Demo ScaleScale
CO2
CaCO3
CaSO4
CaO
Conversion (X)
Reactivity (dX/dt)
SO2
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
0.00
0.35
0 50 100 150 200
t (s)
X CaO
1
2
Particle Models: CaO conversion to CaCO3Ca
O c
onve
rsio
n
Time (s)
Typical conversion of CaO particles to CaCO3
( )(1 ) 1 ln(1 )
(1 ) 1 1 ln(1 ) 1
− − Ψ −=
− + − Ψ − − Ψ
s o s
o
k S C X XdXZdt Xβ
ε
Maximum CO2 carrying capacity under the chemical fast reaction regime
Cycle 1Cycle 2
Cycle 3Cycle 4Cycle 10
Cycle 20
CaO
con
vers
ion
Time (s)
Cycle 1Cycle 2
Cycle 3Cycle 4Cycle 10
Cycle 20
CaO
con
vers
ion
Time (s)
1. Chemically controlled
CaO
CO2
2. Diffusion/Chemically controlled
CaO
CO2
CaCO3
Reaction rate kinetics: Random Pore Model
Ref: Grasa et al. AIChE Journal, 2009, (55) 1246-1255
Effect of number of cycles on sorbent conversion
XN
XN
Reactivity fast enough for circulating fluidized beds
kso (m4/kmol.s) Eak (kJ/kmol) Do (m2/s) EaD(kJ/kmol)
0.54*10-5 20.3*103 3.85*10-6 160*103
Kinetic parameters
Changes of textural properties during cycling
Sintering of the sorbent
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Average activity of the solid in a Ca-looping
Ref: Grasa et al. Ind. Eng. Chem. Res. 2006, 45:8846-8851Abanades, Chemical Eng. Journal 2002, 90: 303-306Rodríguez et al. Chemical Eng. Journal, 2010, 156: 388-394
NR
NR
N FFFFr
)( 0
10
++
=−
Sorbent decay conversion
Continuous system: Particles with different number of cycles
∑∞
=
=1N
NNave XrX
Average activity of the particles in the system
Rapid decay during initial cycles Residual conversion
(0.07-0.10) after hundreds of cycles
r
r
N XNk
X
X ++
−
=
11
1
Other aspect to consider:•Presence of SO2 in the Ca-looping•Partial carbonation and calcination of the sorbent
F0
F0
FR
FR
Fgas+FCO2
Fgas FCO2
CalcinerCarbonator
Carbonation: 650 ºCCalcination:850 ºC
K=0.52Xr=0.075
0
0.1
0.2
0.3
0.4
0.5
0.00 0.05 0.10 0.15 0.20
FO/FRX a
ve
Effect of Fo on Xave
Strategies of operation:•Low Xave and high FR•High Xave and low FR
FCO2 capt = FR * Xave
EXPERIMENTAL
MODELLING
Particle models OD/1D Models 2D/3D Models
Post-combustion CO2 capture using carbonate looping
Lab ScaleSmall pilot plant scale
Pilot plant scale (1.7 MWt) Demo ScaleScale
CO2
CaCO3
CaSO4
CaO
Conversion (X)
Reactivity (dX/dt)
SO2
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Small pilot-plant facility: Description
Small pilot plant at INCAR-CSIC (30 kWt)
Two interconected circulating fluidized beds
Carbonator reactor
CARB
ON
ATO
R
CALC
INER
Simulatedflue gas (CO2)
AirCoal
Clean flue gasCO2
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Main features:
• Two CFB reactors (Height~6.5 m, diameter=100 mm)
• Electrically heated
• Measurement port (temperature, pressure, gas composition)
• Solid circulation measurements
• Solid samples characterization (TG analysis, C/S analyzer)
Ref: Rodriguez et al. AIChE J 2011, 57 (5) 1356-1366
Steady state:Defined as the situation where carbonator and calciner temperature, pressuredrops, inlet gas flows and outlet gas concentration remain constant for aperiod of time of at least 10-20 minutes.
Some measured experimental parameters:•Average carbonation temperature•Inventory of solids•Inlet CO2 concentration and total flow•Outlet CO2 concentration•Carbonate content of entering and exiting solids•Average CO2 carrying capacity of solids•Solid circulation rates
Small pilot-plant facility: Experimental results
Main achievements:
• Has completed 450 h of operation
• Max. CO2 capture efficiency: 97 %
• Absorption capacity up to 7 molCO2/m2s)
0
20
40
60
14:05 14:15 14:25 14:35 14:45 14:55 15:05Inve
ntor
y of
sol
ids
(cm
H2O
)
Calciner Carbonatorr
0
5
10
15
20
25
14:05 14:15 14:25 14:35 14:45 14:55 15:05
Con
cent
ratio
n (%
)
CO2O2O2 probe
QT= 19 m3/h, νCO2 = 0.12, Xave= 0.08
500
600
700
800
900
1000
14:05 14:15 14:25 14:35 14:45 14:55 15:05
Tem
pera
ture
(ºC
) Carbonator Calciner
CO2~2.5%
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Description of the IFK (University of Sttutgart) 10 kWth facility
Ref: Charitos et al. Int. J. Green. Gas. Con., 2010, (4) 776-784
Main features:• A CFB (height=12m) and a BFB• Electrically heated• Measurement ports (temperature, pressure, gas composition)• Solid circulation measurements• Cone vale to control sorbent flow between reactors• Posibility of oxy-fuel combustion in the BFB calciner
Model validation in two experimental facilities: IFK and CSIC
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
FCa Xcalc from calciner
FCa Xcarb to calcinerFCO2 from flue gas
FCO2 (1-Ecarb)
Carbonator reactor concept
Initial assumptions carbonator reactor:•Instantaneous and perfect mixing of the solids•Plug flow for the gas phase
Overall mass balance in the carbonator
Carbonator reactor
NCaO
Xave
in CO2
in CO2inCO2carb F
FF)(E efficiencyn Carbonatio −=
CO2 reacting with CaO in the bed
CO2 removed from the gas phase
CaCO3 formed in the circulating stream of CaO= =
Ref: Rodriguez et al. AIChE J 2011, 57 (5) 1356-1366
0
20
40
60
80
100
14:05 14:25 14:45 15:05
Eca
rb (%
)
0
0.03
0.06
0.09
0.12
0.15
νCO
2
Ecarb Ecarb_eq CO2
Post-combustion CO2 capture using carbonate looping
in CO2
in CO2inCO2carb F
FF)(E efficiencyn Carbonatio −=
Continuous measurement of Ecarb during an experimental run:
•Flue gas fed to the carbonator
•CO2 concentration at the inlet and exit of the reactor
CO2 mass balance in the systemCO2 reacting with
CaO in the bedCO2 removed from
the gas phaseCaCO3 formed in the
circulating stream of CaO= =
Tcarb = 655 ºC, WCa = 260 kg/m2, nCO2 = 0.12, Xave= 0.08
CARB
ON
ATO
R
CALC
INER
Simulatedflue gas (CO2)
AirCoal
Clean flue gasCO2
Ftotal
CCO2 in
CCO2 out
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Post-combustion CO2 capture using carbonate looping
Experimental measurement
CARB
ON
ATO
R
CALC
INER
Simulatedflue gas (CO2)
AirCoal
Clean flue gasCO2
Supply of active flow of CaO
XcalcXcarb
FCa
FCO2
( )calcaveCacarbCO XXFEF2
−≤
CO2 mass balance in the systemCO2 reacting with
CaO in the bedCO2 removed from
the gas phaseCaCO3 formed in the
circulating stream of CaO= =
Ref: Rodriguez et al. Energy Procedia 2011, (4) 393-401
( ) 2COcarbcalccarbCa3 FEXXF
CaOofstreamgcirculatintheinformedCaCO
=−=
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Post-combustion CO2 capture using carbonate looping
( )e2COavesave ffXkr −=
CO2 mass balance in the systemCO2 reacting with
CaO in the bedCO2 removed from
the gas phaseCaCO3 formed in the
circulating stream of CaO= =
Particles reacting in the carbonator
>
<=
*tfor t 0
*t tif *t
Xr
N
N
>
<=
*tfor t 0
*t tif *t
Xr
ave
ave
Simplified reaction rate
aCaActiveCa fNN =
−= τ
−*t
a e1f
CaOFCaN
=τt*
Xave
Ref: Alonso et al. Chem. Eng. Journal, 2009, (64) 883-891
( )e2COavesaCareactor
ActiveCa ffXkfNdtdXN
bedtheinCaOwithreacting2CO
−ϕ=
=
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Apparent reaction rate=0.43 s-1
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150 200
faNCaXave, mol/m2
Ecar
b
ExperimentalModel
Comparison of CO2 capture efficiencies and CO2 removal rates in the reactor
CO2 mass balance in the systemCO2 reacting with
CaO in the bedCO2 removed from
the gas phaseCaCO3 formed in the
circulating stream of CaO= =
Post-combustion CO2 capture using carbonate looping
( )2CO
e2COavesaCacarb F
ffXkfNE
−ϕ=
FCO2= 7 mol/m2s
The CO2 capture in the reactor is controlled mainly by the kinetics of the carbonation reaction
Experimental determination of ks
ϕ close to unity
aveaCO
CaOactive Xf
FN
2
=τ
Experimental data:
Inlet CO2 Vol. % = 11.4 for IFK &16.5 for INCAR-CSIC
Tcarb= 634-660 °C, Xmax,ave= 0.08-0.23
Ref: Charitos et al. Ind. Eng. Chem. Res. Submitted for publication. Common paper between IFK and INCAR-CSIC
Model validation in two experimental facilities: IFK and CSIC
Critical active space time at which
ECO2/Eeq>90%:
• IFK data set: 0.025 h
• INCAR-CSIC data: 0.008 h
Main differences between both series of experimental and calculated data• Different inlet CO2 concentration (11.4% IFK, 16.5% INCAR)
• Different limestone (IFK limestone less reactive, ks=0.20s-1)
Active space time
( )e2COsactivecarb ffkE −ϕτ=( )
2CO
e2COavesaCacarb F
ffXkfNE
−ϕ=
EXPERIMENTAL
MODELLING
Particle models OD/1D Models 2D/3D Models
Post-combustion CO2 capture using carbonate looping
Lab ScaleSmall pilot plant scale
Pilot plant scale (1.7 MWt) Demo ScaleScale
CO2
CaCO3
CaSO4
CaO
Conversion (X)
Reactivity (dX/dt)
SO2
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Next steps in Ca-looping development: 1.7 MWt pilot plant
Facility area
FP7 “CaOling” Project:Development of postcombustion CO2 capture with CaO in a large testing facility: “CaOling”
Main objective:
To advance in the experimental validation of the carbonate looping cycle (at a 1 MWt scale range) and demonstrate that this is a low cost, highly energy efficient CO2 capture technology, suitable for retrofitting coal combustion power plants
Operation will start in September 2011
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
Calciner operating under air or oxy-combustion
conditons
Double loop seal to control solid circulation
between reactors
Removable cooling bayonet tubes to change
heat extraction in reactors
O2 and CO2 tanks and gas mixer, to change oxy-combustion ratio
Calciner gas heater and indepent steam inyection
Gas velocities similar to those encountered in CFB
boilers (3-5 m/s)Continuous coal and
limestone feeding system
Next steps: 1.7 MWt pilot plant
Complete instrumentation (temperature, pressure,
solid samples)
Next steps: 1.7 MWt pilot plant
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
SOME OBJECTIVES:• To gain the necessary design data and experience for rapid scale-up of the technology, building
experimentally validated models from the careful interpretation of results produced from lab-scaleprototypes and from the experimental campaigns in a 1 MW test facility.
• To evaluate and optimise the concept in operating conditions equivalent to large-scale industrial unitsand integrated in a commercial plant. To analyse the controllability and stability of the process
• To find the optimum set of operating conditions to minimize sorbent make-up flow cost (calcinationtemperatures, O2/CO2 ratios in the calciner, requirement for steam in the carbonator and calciner, bestsuitable approach for SO2 capture, etc).
• Modelling work. Next steps:• Solid distribution of the whole system: pressure balance approach
(inventory of solids in the reactors, solid circulation rates,…)• 2D/3D reactor models including the more complex fluid-dynamics of large
scale systems• CFB Calciner reactor: oxy-fuel combustion+calcination
Postcombustion Calcium Looping is a rapidly developing technology successfullycharacterized at small pilot plant scale.
A simple carbonator reactor model (CSTR for solids and PF for gas) is shown to fitreasonably well the available results in CFB mode of operation.
The model highlights the importance of sufficient solid inventories and solidcirculation rates for a given activity of the solids and a given flow of flue gasesentering the carbonator.
The extrapolation of results to large scale CFB carbonator reactors anticipates captureefficiencies over 90% in operating at realistic conditions (similar to those present incommercial CFBC units) even with CaO particles in their residual activity after 10s to100s of carbonation-calcination cycles.
Carbonation efficiency correlates well with active space time, which combines themain carbonation operation parameters.
A flexible experimental facility has been constructed in La Pereda Power Plant (Spain)aiming to validate Calcium Looping technology in the 1MWs size.
Conclusions/Remarks
Post-combustion CO2 capture using Ca-loopingWorkshop on Mathematical Modelling of Combustion
"Post-combustion CO2 capture by Ca-looping"
Workshop on Mathematical Modelling of Combustion
23-25 May, Santiago de Compostela, Spain
Thank you for your [email protected]
•This work has been carried out as part of the FP7 “CaOling“ Project.•Special thanks to IFK (Prof. Scheffknecht) for permission to use some of their data and figures in this presentation.