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transcript
Calcium Looping Cycles – Sorbent Particle Size Change
and Steam Reactivation
Y. Wu1,2, J. Blamey2, E.J. Anthony1 and P.S. Fennell21CanmetENERGY2Imperial College
1st
High Temperature Solid Looping Cycles IEA Network Meeting
Oviedo, Sept. 16, 2009
Process Overview
Carbonation
~ 600 ºCFluidized Bed
Calcination
~ 900 ºCFluidized Bed
CaCO3 CaO
Sequester
>90 mol% CO2Fuel
O2
New or Existing
Combustor
Fuel
Air
Flue Gas8% < CO2 < 15%
Heat
Heat
Vent
< 1 mol% CO2
Limestone
Oxy-fuel CFBC
CO2
Looping Combustion
CaO (s) + CO2
(g) ↔
CaCO3
(s)
Gasifier or Steam
Methane Reformer
FuelSyngas
CO, CO2 , H2 , H2 O
Oxidant
Conventional Combustionor
H2
Production
Sorbent Deactivation1st carbonation
2 μm
a
1st carbonation
2 μm
a Sintering
2 μm
b
30th carbonation
2 μm
b
30th carbonation
Sorbent Decay
Abanades, J., Alvarez, D., Energy & Fuels 17 (2003), 308-315
Grasa, G.S. and Abanades, J.C., Ind. Eng. Chem. Res. 45 (2006), 8846-8851
∞
∞
++
−
= XkN
X
X N
11
1
ObjectivesDetermine the effect of steam reactivation on spent sorbent after repeated carbonation and calcination cyclesInvestigate the hydration rate with atmospheric pressure steamInvestigate sorbent particle size changes during repeated cycles and steam reactivationDiscuss the influence of particle size change in the context of attrition studiesTo separate the effects of particle diameter loss due to attrition from those caused by densification of the particles
Experimental ConditionsCa-based sorbent – limestones
Havelock (0.71-1.00 mm, NB, Canada)Kelly Rock (0.60-0.80 mm, NS, Canada)Katowice (0.40-0.80 mm, Poland)Purbeck (0.71-1.00 mm, UK)
Important to note that the SiO2
in the Purbeck limestone is present mainly as distinct flint pieces (which is a hard, sedimentary form of SiO2
); this is not the case for the other limestones.
Experimental Conditions
Carbonation650°C, 5 min
Calcination900°C, 5 min
Gas composition15% CO2, N2 and He balance
Atmospheric pressure, up to 50 cyclesTwo types of runs
Bulky sample (~20 mg) for reactivity and steam reactivationSingle particle for particle size analysis
0
100
200
300
400
500
600
700
800
900
1000
0 20 40 60 80 100 120
Time, min
Tem
pera
ture
, °C
FirstCalcination
Cycle 1 Cycle 2 Cycle 3 Cycle nCycle 4 Cycle 5
Experimental Conditions
Steam reactivationBulky sample (~20 mg)After 10 cycles of carbonation/calcinationAtmospheric pressure, 130°C, 5 min
Particle images captureSingle particlesRaw particle, after 1st calcination, 1st
cycle, 4th cycle……
Seben Optical Microscope
Steam
Generator
Hydrator
Steam
HPLC PumpDI Water
Reference Dimension
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 10 20 30 40 50 60
Number of cycles
Car
ryin
g ca
paci
ty
Bulk sample, no reactivation
Bulk sample, steamreactivation after 10 cyclesParticle HL2, steamreactivation after 10 cyclesParticle HL3, steamreactivation
after 10 and 14 cycles
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 5 10 15 20 25
Number of cycles
Car
ryin
g ca
paci
ty
HavelockKelly RockKatowicePurbeck
Effect of Steam Reactivation
Reactivity decay: HL<KW≈PB<KRSimilar to previous findings for Havelock and Purbeck
Steam reactivation, 130°C, 5 min
Second reactivation, 130°C, 5 min
Havelock
Steam Hydration Rate
0.80
0.82
0.84
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
0 2 4 6 8 10 12
Hydration time, min
CaO
con
vers
ion
to C
a(O
H) 2
Steam reactivation after 20 cycles
Steam temperature 160°C
Steam reactivation after 20 cycles
HavelockKelly RockKatowicePurbeck
Steam temperature 160°C
Atmospheric pressure steam, 130°CReactivation after 10 cyclesCalcined in N2 to determine the extent of CaO conversion>90% conversion in ~2 minPrevious work has used up to 30 minutes, and pressurised steam
Particle Size Shrinkage
~7% size shrinkage for Havelock and Katowice
Size decay: ∞
∞
++
−
= dNk
d
ds
N
11
1
0.91
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1.00
1.01
0 (ori
gin)
0 (1s
t calc
)1 (
carb)
1 (ca
lc)4 (
carb)
4 (ca
lc)10
(carb
)10
(calc
)20
(carb
)20
(calc
)50
(carb
)50
(calc
)
Number of cycles
Nor
mal
ized
val
ue
(b)
Katowice
LengthEquivalent diameter
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1.00
1.01
0 (ori
gin)
0 (1s
t calc
)1 (
carb)
1 (ca
lc)4 (
carb)
4 (ca
lc)10
(carb
)10
(calc
)20
(carb
)20
(calc
)50
(carb
)50
(calc
)
Number of cycles
Nor
mal
ized
val
ue
(a)
Havelock
LengthEquivalent diameter
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 10 20 30 40 50 60
Number of cycles
Car
ryin
g ca
paci
ty PB bulk samplex Particle PB3+ Particle PB4
Larger size decayvs. better reactivity?
Reactivity decay: HL<KW≈PB<KRSize decay: HL ≈KW>PB ≈KR
Particle Size Shrinkage (Single Particle)
PB4
PB3
PB3
PB4
Reactivity decay: PB4<PB3
Size decay: PB4>PB3
Less than 2% size shrinkage for Kelly Rock and Purbeck (4% for PB4)
0.980
0.985
0.990
0.995
1.000
1.005
1.010
0 (ori
gin)
0 (1s
t calc
)1 (
carb)
1 (ca
lc)4 (
carb)
4 (ca
lc)10
(carb
)10
(calc
)20
(carb
)20
(calc
)50
(carb
)50
(calc
)
Number of cycles
Nor
mal
ized
equ
ival
ent
diam
eter
(c) Kelly RockParticle KR1Particle KR2
x Particle KR3
0.95
0.96
0.97
0.98
0.99
1.00
1.01
0 (ori
gin)
0 (1s
t calc
)1 (
carb)
1 (ca
lc)4 (
carb)
4 (ca
lc)10
(carb
)10
(calc
)20
(carb
)20
(calc
)50
(carb
)50
(calc
)
Number of cycles
Nor
mal
ized
equ
ival
ent
diam
eter
(d)
Particle PB1Particle PB2Particle PB3Particle PB4
Purbeck
The Influence of SiO2
Purbeck and Kelly Rock have more SiO2 (3-4%) than Havelock and Katowice (~1%).SiO2 may distribute through the particle or exist as distinct flint pieces.Higher SiO2 content spread throughout the particle enhances sintering.
Greatly reduced porosityArea of increased sintering
The flint forms a network to prevent the particle from shrinking. Manovic, V. et al., Fuel 88 (2009), 1893-1900
1.37% SiO2
10.21% SiO2
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
0 (ori
gin)
0 (1s
t calc
)1 4 10
10 (h
yd)
11 (c
arb)
11 (c
alc)
1414
(hyd
)15 20 25 50
Number of cycles
Nor
mal
ized
equ
ival
ent d
iam
eter Particle HL1, no
reactivation
Particle HL2, steamreactivation after 10cyclesParticle HL3, steamreactivation after 10 and14 cycles
Steam reactivation
Particle Size Change During Steam Reactivation
Havelock
Original 10 CyclesSteam Reactivated
Porosity Changes
Molar conservation of Ca
)1(13
ct
ct r
r εε −⎥⎦
⎤⎢⎣
⎡−=
)1(1 0
3
0
3
3 ερρ
ε −⎥⎦
⎤⎢⎣
⎡−=
cCaCOCaO
CaOCaCOc r
rM
M
0.75
0.80
0.85
0.90
0.95
1.00
1.05
0 (1s
t calc
)1 (
carb)
1 (ca
lc)4 (
carb)
4 (ca
lc)10
(carb
)10
(calc
)20
(carb
)20
(calc
)50
(carb
)50
(calc
)
Number of cycles
Nor
mal
ized
por
osity
HavelockKatowiceKelly RockPurbeck (average of PB1, PB2, and PB3)PB4
(a)
ε0
–
porosity of original particle
εc
–
porosity after first calcination
εt
–
porosity at time t 0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
0 (1s
t calc
)
1 4 10
10 (h
yd)
20 50
Number of cycles
Nor
mal
ized
por
osity Particle HL1, no reactivation
Particle HL2, steam reactivationafter 10 cycles
(b)
Particle Size Changes and Attrition Study
Particle size distribution (PSD) is an important parameter in fluidized bed combustion.Some previous work has measured changes in size distribution and attributed these changes solely to attrition.Particle size change through densification has previously been ignored in the model, but may be important.
Population balance model:
Saastamoinen, J. et al., Powder Technol. 187 (2008), 244-251
Final simplified PSD equation
Conclusions
Steam reactivation under atmospheric pressure can restore the CO2 carrying capacity of the spent sorbent.Steam hydration is relatively quick.Particle size can reduce after repeated cycles.Particle size changes due to repeated cycles should be taken into account in attrition studies in CO2 looping combustion.
Acknowledgement
Financial support from Kaust program by Imperial College London and from Natural Resources Canada is sincerely appreciated.Other colleagues of Dr. Paul Fennell’s group: Dr. Nick Florin, Charlie, Kelvin, Nigel