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

Overview

IntroductionObjectivesExperimentalResultsConclusion and future work

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.

Future Work

In-situ steam reactivation apparatusFriability of reactivated particles

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

Thank you!