sulfation rates of particles in cal reactors - oxyfbc home

SULFATION RATES OF PARTICLES IN CaLREACTORS

J.M. Cordero, B. Arias, M. Alonso, J.C. Abanades

CSIC‐INCAR [email protected]

IFK-UNIVERSITY OF STUTTGART, STUTTGART Jun 2012

www.caoling.eu

SO2 capture in CaL post‐combustion technologies: general sketch

CFBCARBONATOR

STANDARDPOWER PLANT

Concentrated CO2

Coal CaCO3CaO Purge

CaCO3

CaO

Flue Gas

Flue gas“without” CO2

Coal Air

O2

Air

N2

ASU

OXY-CFBCALCINER

Power OUT

Power OUT

CO2

SO2CaSO4 CaSO4

S S

There are other pollutants that can affect the CO2capture efficiency

Sulfation reaction in the three main processes mustbe investigated

SO2 capture in CFBCs

Concentrated CO2

CoalCaCO3 CaO Purge

CaCO3

CaO


Coal Air

O2

Power OUT

Power OUT

CFBC CARBONATOR OXY-CFB CALCINER

850-900 ºC500 - 3000 ppm SO210-15% CO2P = 1 atm

~ 650 ºC100-500 ppm SO210% CO2P = 1 atm

870 - 930 ºC500 - 3000 ppm SO2>70% CO2P = 1 at

Grasa et a´, IEC 2007 T = 900 ºCdp = 300-600 µm2200 ppm SO2

Grasa et al, Ind. Eng. Chem. Res. 2008; 47:1630–1635

Sulfation is a “well known” reaction in CFBC environmentsSeveral studies suggest that sulfation reactions will be enhanced when using CaL

purges

Flue Gas

0

0.1

0.2

0.3

0.4

0 50 100 150

XCaSO

4

t (min)

Cycle 1

Cycle 15

Cycle 100

SO2 capture in the CaL carbonator

Concentrated CO2

CoalCaCO3 CaO Purge


Coal Air

O2

Power OUT

Power OUT


850-900 ºC500 - 3000 ppm SO210-15% CO2P = 1 atm

~ 650 ºC100-500 ppm SO210% CO2P = 1 atm

870 - 930 ºC500 - 3000 ppm SO2>70% CO2P = 1 at

Grasa et a´, IEC 2007

Flue Gas

CaCO3

CaO

T = 650 ºCdp = 63-100 µmGas phase = 500 ppm SO2Oxygen in all cases > 5%

• The experimental procedure: sulfation after N cycles of calcination-carbonation.

• The initial rate of sulfation is clearly affected by SO2 concentration.

• Apparent first order with respect to SO2, maintained along cycles.

SO2 concentration effect over Compostilla limestone.

SO2 capture in the CaL carbonator: effect of the SO2 concentration

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0 400 800 1200

X CaS

O4

t (s)

500 ppm1000 ppm2000 ppm3000 ppm0 0,000

0,001

0,002

0,003

0,004

0,005

0,00 0,01 0,02 0,03 0,04 0,05

X C

aSO

4/t(

s-1 )

CSO2 (mol/m3)

Compostilla N=1Imeco N=1Enguera N=1Compostilla N=20

00

Carbonation conditions: particle size effect

• Reaction rates similar to both sizes homogeneous model of sulfation

Effect of the particle size after the first calcination and 20 calcination/carbonation cycles for Compostillalimestone.

Constant concentration of CaSO4 through the particle


SO2 capture in the CaL carbonator: effect of the particle size

K. Laursen et al, Fuel 2000; 79:153–163

SULFATION

Shell Network Homogeneous

0,00

0,05

0,10

0,15

0 100 200 300

X CaS

O4

t (s)

63-100 µm400-600 µm63-100 µm400-600 µm

N = 1

N = 20N = 20

N = 1

0

Carbonation conditions: cycles effect

0

0,1

0,2

0,3

0 300 600 900 1200

X CaS

O4

t (s)

N=1

0

0,1

0,2

0,3

0 300 600 900 1200X C

aSO

4t (s)

N=10N=20N=50

N=10

N=20 N=50

Evolution of CaO conversion to CaSO4 with time. Comparing the effect of the number of cycles.


• For N = 1, sulphation rate falls sharply after 10 minutes of reaction, due to pore blockage.

• For N > 1, there is a smoother transition between fast and slow stages of reaction. This transition is due to theproduct layer diffusion, that produces a change of regime when the critical thickness is reached.

SO2 capture in the CaL carbonator: effect of N cycles

Carbonation conditions: fitting with the Random Pore Model

0

0,1

0,2

0,3

0 300 600 900 1200

X CaS

O4

t (s)

N=1

0

0,1

0,2

0,3

0 300 600 900 1200X C

aSO

4t (s)

N=10N=20N=50

N=10

N=20 N=50

Comparison of the experimental values with those calculated for Compostilla limestone, fordifferent number of cycles.


• For N = 1, the model only fits well from a conversion up to 0.1. From that value, the model overpredicts theresults (pore blockage)

• For N = 50, the RPM fits well over all the range of conversion, showing that the product layer can full developwithout any geometrical restriction.

SO2 capture in the CaL carbonator: fitting by the Random Pore Model

B. Arias et al, AIChE(in press)

SO2 capture in the CaL calciner

Concentrated CO2

CoalCaCO3 CaO Purge

CaCO3

CaOFlue Gas


Coal Air

O2

Power OUT

Power OUT


850-900 ºC500 - 3000 ppm SO210-15% CO2P = 1 atm

~ 650 ºC100-500 ppm SO210% CO2P = 1 atm

870 - 930 ºC500 - 3000 ppm SO2>70% CO2P = 1 at

Grasa et a´, IEC 2007

Sulfation in the Oxy‐CFB calciner: effect of N cycles

T = 930 ºCdp = 63-100 µmGas phase = 500 ppm SO2, 70% CO2Oxygen in all cases > 5%

• The sulfation pattern is different from that shown for CFBC conditions.

• The final conversion to CaSO4 and the initial slope of the sulfation curves decreased generally with the cycles.

• Since the surface area S only can decrease while cycling, two scenarios are possible for both limestones:

1. The sulfation pattern is homogeneous (pseudo-homogeneous) from the beginning.

2. The sulfation pattern starts being unreacted core, but between N = 1 and 20, it transforms into homogeneous.

For checking the sulfation pattern at oxy-CFB conditions, experiments varying the particle diameter wereperformed.

0

0.1

0.2

0.3

0.4

0.5

0 900 1800 2700 3600

XCaSO

4

t (s)

cycle 1

cycle 20

cycle 50

Compostilla Enguera Brecal

0

0.1

0.2

0.3

0.4

0.5

0 900 1800 2700 3600

XCaSO

4

t (s)

cycle 1

cycle 20

cycle 50

cycle 175

0

0.1

0.2

0.3

0.4

0.5

0 900 1800 2700 3600

XCaSO

4

t (s)

cycle 1

cycle 50

cycle 150

Sulfation in the Oxy‐CFB calciner: effect of the particle size


• The initial rate of sulfation is similar whichever is the particle diameter and the number of cycle N, so:

The sulfation pattern is pseudo-homogeneous from the beginning

Compostilla

1st calcination N calcinations

SULFATION

SULFATION

0

0.1

0.2

0.3

0.4

0.5

0 500 1000 1500 2000

XCaSO

4

t (s)

36‐63 µm

63‐100 µm

100‐200 µm

N = 1

0

0.1

0.2

0.3

0.4

0.5

0 500 1000 1500 2000

XCaSO

4

t (s)

63‐100 µm

400‐600 µmN = 50

Sulfation in the Oxy‐CFB calciner: effect of the particle size


Enguera

• The sulfation rate depends on the particle size, but:

• The three smaller particle sizes studied behavior is almost homogeneous for cycle 50 (initial slope).

• The larger particle size is always non homogeneous, on the contrary that occurred for Compostilla limestone.

0

0.1

0.2

0.3

0.4

0.5

0 500 1000 1500 2000

XCaSO

4

t (s)

36‐63 µm

63‐100 µm

100‐200 µm

400‐600 µm

N = 1

0

0.1

0.2

0.3

0.4

0.5

0 500 1000 1500 2000

XCaSO

4

t (s)

36‐63 µm

63‐100 µm

100‐200 µm

400‐600 µm

N = 50

Sulfation in the Oxy‐CFB calciner: effect of the CO2


Comparison of the conversion curves under CO2 atmosphere with those without CO2

• Regardless of the limestone, CO2 did not show important influence over the initial sulfation rate.

• The times and temperatures of exposition to sinterization are insignificant compared to the sulfation rate, so itseffect is despicable.

Compostilla

0

0.1

0.2

0.3

0.4

0.5

0 1000 2000

XCaSO

4

t (s)

0% CO2

70% CO2

N = 1

0

0.1

0.2

0.3

0.4

0.5

0 1000 2000

XCaSO

4

t (s)

0% CO2

70% CO2

N = 50

Sulfation in the Oxy‐CFB calciner: effect of the SO2 concentration


• The sulfation rate increases with SO2 concentration in gas phase, as was expected, following an apparent firstorder.

Enguera N = 50

0

0.03

0.06

0.09

0.12

0 50 100

Xs

t (s)

1000 ppm

1500 ppm

3000 ppm

0

0.001

0.002

0.003

0 1000 2000 3000 4000

∆XCaSO

4/∆t (s

‐1)

CSO2 (ppm)

CompostillaEnguera

SO2 capture in CaL post‐combustion technologies

Conversion to CaSO4 curves for Enguera limestone.

T = 650, 850, 930 ºCdp = 63-100 µmSO2 concentration = 500 ppm SO2 (balance in air)Oxygen in all cases > 5%

• At the view of the graphs, it appears that a change of mechanism is produced some point between 850-930 ºC. Supporting this:

• The conversion curve for 930 ºC is below the expected considering the others at lower temperature.

• The final conversion of the interval shows a maximum at 850 ºC.

• There is a number of explanations,

• Blockage of small pores due to improved kinetics (difficult N = 50)

• Sintering at higher temperatures (short times)

• Change in sulfation mechanism

• Others

0

0.1

0.2

0.3

0.4

0 200 400 600 800 1000

XCaSO

4

t (s)

650 °C

850 °C

930 °C

N = 50

SO2 capture in CaL post‐combustion technologies

Conversion to CaSO4 curves for Compostilla limestone.

T = 650, 850, 930 ºCdp = 63-100 µmSO2 concentration = 2000 ppm SO2 (balance in air)Oxygen in all cases > 5%

• For Compostilla limestone, the result was the same.

0

0.1

0.2

0.3

0.4

0 200 400 600 800 1000

XCaSO

4

t (s)

650 °C

850 °C

930 °C

N = 50

Non Homogeneous(Unreacted Core)

Homogeneous

Pseudo-Homogeneous(Network)

Unreacted Core: Grains separated by micropores. Only reacts the external surface area.

Sulfation patterns

Network: Grains gathered together, only reacts the external surface area of this groups, remaining slightlyor unsulfated their core.

Homogeneous: The surface area of the particle reacts homogeneusly, independently of the radius position.

XS

dP

dP

XS

Sulfation

Sulfation

Sulfation

Sulfation patterns in CaL systems

Conditions of reactionOperating conditions

Properties of the sorbentType of limestonedP

Modifications of the internal structureConversion (time of reaction)N (normally N , dpore and S )

Characteristic of some limestones, specially with low

N , high particle size and reaction conditions typical of

CFBCs and CFB calciners.

Common for all types of CaL particles with high N and dp below 200 µm, in all reactors.

1st calcination Cycle N Cycle M M >> N

Unreacted core Pseudo-homogeneous Homogeneous

SULFATION

SULFATION

SULFATION

Future work

• To study the use of the purge of the Ca-looping cycles in a combustor tocapture the SO2 before it enters the system of CO2 capture. This meansstudying the sulfation reaction under the conditions that exist typically incombustors.

• To study the sulfation behavior of samples of sorbents from La Pereda powerplant.

• To study the competence between carbonation and sulfation reactionscarried at the same time: co-capture.

Conclusions

•The apparent order of reaction was one for sulfation reaction at carbonatingand calcining conditions in the Ca-looping CO2 capture systems.

• The CO2 concentration did not affect the initial sulfation rates.

• The number of cycle, N, affects the pattern of sulfation, becoming it morehomogeneous with higher N. Spent enough CaL sorbents will sulfatehomogeneously in both carbonator, CFBC and calciner. For low values of Nand moderate to high particle sizes, the pattern usually is unreacted core typefor many limestones.

• The reactor that achieved a better conversion to CaSO4 was the CFBC.

• The results indicate that the post-combustion Ca-looping carbonators andcalciners would be effective reactors for capturing SO2 from flue gases.

Acknowledgements

• This work is partially funded by the European Commission (FP7-CaOlingproject).

• J.M.C. acknowledges a predoctoral research from FICYT.

SULFATION RATES OF PARTICLES IN CaL REACTORS

J.M. Cordero, B. Arias, M. Alonso, J.C. Abanades

CSIC‐INCAR [email protected]

IFK-UNIVERSITY OF STUTTGART, STUTTGART Jun 2012

THANKS FOR YOUR ATTENTION

www.caoling.eu

sulfation rates of particles in cal reactors - oxyfbc home

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