kinetics study for o2 absorption/ desorption using a

1st International Oxyfuel Combustion Conference 7th – 11th Sept., 2009 Cottbus, Germany

Kinetics Study for O2 Absorption/ Desorption Using a Cobalt BasedDesorption Using a Cobalt Based

Oxygen Carrier

Teng ZHANG, Zhen-shan LI, Ning-sheng CAI

10th, Sept., 2009

Key Laboratory of Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing, CHINA

Outline

Introduction

Research

Perovskite

Co-based O2 carrier

• TGA and SEM

• Dynamics model

• Fixed bed

• Dual fixed beds

• Fluidized bed

1st International Oxyfuel Combustion Conference 2

Summary

IntroductionOxyfuel combustion — capturing CO2 from the use of fossil fuel


IntroductionAir

Oxygen production：1、Cryogenic ASU Cryogenic ASU

ASU

P1 ,T1

PO2,out ,TO2,outPO2,in ,TO2,in

O2

different boiling points of O2 and N2

2、Membrane separationselective permeation of O2

3、Pressure swing adsorption（PSA）

AirOff gas

PN2,in ,TN2,in

PN2,out ,TN2,outN

O2selective reversible adsorption of N2(not O2)

onto molecular sieve sorbents at high pressures

AirVacuum

N2

Boiling point at 1 atm - O2: 90K, N2: 77K

Bed A Bed BPSA Membrane

separation


O2 O2 O2

O2

IntroductionCryogenic ASU takes ~25% of the total investment costand consumes ~15% of the total electricity produced

Only O2-CO2 mixed gas with O2

concentration between 20 40%


concentration between 20~40% is needed, rather than pure O2

Introduction

Air Ceramic Autothermal Recovery (CAR

CO2、H2O

y (from BOC)storage and release of O2 in two or multiple fixed-bed reactors containing perovskite-fixed-bed reactors containing perovskite-type material operated at high temperatures

O Oxygen

' '1 - 1 - 3 -A A B B Ox x y y perovskite-type

Carbon Dioxide

Oxygen

Storage

Oxygen

Release

O2、CO2、H2ON2

BoilerCarbon Dioxide


WaterFuel

Major challenge of perovskite material

When using CO2 as purge gas during the O2 release stage, carbonate (SrCO ) was formed

2.2.60.50.50.90.1

0 15OO0 25Fe0 5CoOO0 05La0 9SrCO0.9COOFeCoSrLa

(SrCO3) was formed

232233 0.15OO0.25Fe0.5CoOO0.05La0.9SrCO

In the next step, O2 storage stage, the carbonate(SrCO3) will decompose and CO2 will be released into air, diluted by N2

22.2.60.50.50.90.1

2232233

aN0.9COOFeCoSrLaaN0.15OO0.25Fe0.5CoOO0.05La0.9SrCO

This will result into failing to capture CO2 from flue gas.

Using pure steam to replace flue gas as purge gas can solve this


g p p g p g gproblem, but it will require more energy.

Research · PerovskiteThe main element that has carbonation with CO2 is Sr, So Sr => Mg

O Storage Process Carbonation Process

4.04.55.0

4.04.55.0

4.04.55.0

LSCF SCCF LM CF

LSCF SCCF LM CF

LSCF SCCF LM CF

10

12

) 10

12

)

O2 Storage Process Carbonation Process

2.02.53.03.54.0

LSCFSCCFLMCFCMCFYBCt C

hang

e (%

)

2.02.53.03.54.0


hang

e (%

)

2.02.53.03.54.0


hang

e (%

) CMCF YBCA

CMCF YBCA

CMCF YBCA

6

8

ht C

hang

e (%

LSCFSCCFLMCFCMCF

6

8

ht C

hang

e (%

LSCFSCCFLMCFCMCF

LSCF SCCF LM CF CM CF



0.00.51.01.52.0 YBC

Wei

ght

0.00.51.01.52.0 YBC

Wei

ght

0.00.51.01.52.0 YBC

Wei

ght

0

2

4

Wei

gh CMCFYBC

0

2

4

Wei

gh CMCFYBC

YBCA

YBCA

YBCA

0 100 200 300 400 500 600 700 800 900 10000.0

Temperature ( ℃)0 100 200 300 400 500 600 700 800 900 1000

0.0

Temperature ( ℃)0 100 200 300 400 500 600 700 800 900 1000

0.0

Temperature ( ℃)

0 100 200 300 400 500 600 700 800 9001000Temperature (℃ )

0 100 200 300 400 500 600 700 800 9001000Temperature (℃ )

1. After changing Sr to Mg, Carbonation reaction can be weakened, but at the same time, Oxygen capacity will also be reduced.


, yg p y

2. All these five perovskite-type materials cannot avoid carbonation reaction below experimental temperature 950 .

Research · Co-based O2 carrier

Co-based oxygen carrier

After using CO2 to release O2

5

6

7

nge

(%)

LSCF SCCFLM CF

Before using CO2 to release O22

3

4

Wei

ght C

han LM CF

CMCF YBC A

A：CoO B：Co3O4

0 100 200 300 400 500 600 700 800 900 10000

1

Tem perature ( ℃ )

XRD results indicated it does not react with CO2 at high temperature

A：CoO B：Co3O4

higher oxygen capacity and higher reaction rate

1st International Oxyfuel Combustion Conference 9432 26 OCoOCoO theoretical oxygen capacity is 7.11wt%.

Research · TGA

20 cycles with Air/CO at 840

Cycles characteristic

13.6

13.8

800

9001000

20 cycles with Air/CO2 at 840

13.2

13.4

mg) 600

700800

ure

( ℃)

12.8

13

Mas

s (m

300

400500

Tem

pera

tu

12.4

12.6

0100

200


0 50 100 150 200 250 300 350 400 450Reaction time (min)

Research · SEMSEM Analyse

Befo

re Reeactio

n

1.00KX 5.00KX3.00KXAfter m

a

.00 5.003.00

ny cycles


After many cycles，no obvious sinter phenomenon were found in micro structure。

Research · TGA

SO2(2570ppm) effect on oxygen carrier

4

5

6

600

800

1000

(℃)

e (%

)

910℃922℃100000

SO3

(ppm

)

1

2

3

200

400

600

Tem

pera

ture

wei

ght c

hang

e

1000

10000

otal

of S

O2

and

S

0 20 40 60 80 100 120 140

00

Time (min)600 650 700 750 800 850 900

1000

To

Temperature ( ℃ )

TGA Results Theoretical equilibriumdoes not react with SO2 at 910

NO(2790ppm) effect on oxygen carrier

TGA Results with SO2 at 910 .


The weight does not change during the temperature 200-920 。

Research · TGAOxygen absorption

100100100Air

405060708090

vers

ion

(%)

880℃850℃800℃700℃600℃

700℃, Maxi mum r at e

405060708090

vers

ion

(%)

880℃850℃800℃700℃600℃


405060708090

vers

ion

(%)

880℃850℃800℃700℃600℃


Reaction rate increases at 460-700 and decreases

0102030

0 5 10 15 20 25 30

Conv 600℃

500℃480℃460℃0

102030

0 5 10 15 20 25 30

Conv 600℃

500℃480℃460℃0

102030

0 5 10 15 20 25 30

Conv 600℃

500℃480℃460℃

at 700-880 .

Reaction Time (min)Reaction Time (min)Reaction Time (min)

80

100

(%)

100% O2

N2 diluted@ 810

20

40

60

Conv

ersio

n ( 100% O2

80% O260% O240% O220% O2

Reaction rate increases as O2 concentration increases.


00.0 0.5 1.0 1.5 2.0 2.5 3.0

Reaction Time (min)

20% O2

Research · TGAOxygen desorption

100 Ramping rate 10℃/min100 Ramping rate 10℃/min

For either N2 or CO2 diluted O2:40

60

80

onve

rsio

n (%

)

100% O280% O260% O240% O2

N2 diluted

40

60

80

onve

rsio

n (%

)

100% O280% O260% O240% O2

N2 diluted

1. The breakeven decomposition temperature increases with O2

0

20

860 880 900 920 940 960 980

Temperature (℃)

Co 40% O220% O2

0

20

860 880 900 920 940 960 980

Temperature (℃)

Co 40% O220% O2

concentration.

2. They have similar effects.

p (℃)p (℃)

60

80

100

on (%

)

40% O2

Ramping rate 10℃/minCO2 diluted

60

80

100

on (%

)

40% O2

Ramping rate 10℃/minCO2 diluted

0

20

40

Conv

ersio 30% O2

20% O210% O20% O2

0

20

40

Conv

ersio 30% O2

20% O210% O20% O2


820 840 860 880 900 920 940 960

Temperature (℃)

820 840 860 880 900 920 940 960

Temperature (℃)

Research ·Dynamics modelEquilibrium P and T Decomposition

temperature increases with

Temperature1 5

2

(atm

)

N2 diluted

O2 partial pressure

O2 partial pressure1

1.5

al p

ress

ure

CO2 dilutedO2 storage

O2 pa a p essu e

0

0.5

O2

parti

O2 release

800 850 900 950

Temperature (℃)

Thermal dynamic equilibrium


]49.133)1000(78.291)1000(32.193)1000(913.42exp[101325, 232

TTT

ePO

Shrinking-core modelIf the rate is dominated by the diffusion in the air

2 1t

If the rate is dominated by the diffusion in the product layer

1

)(21

t eg dtCCkX

2

32

)(36)1(2)1(31t

dCC

If the rate is dominated by the reaction on the surface

1

3 )(36)1(2)1(31t eA dtCCDXX

2

31

)(6)1(1t

dtCCkX 1

3 )(6)1(1t

dtCeCkX

For TGA experimental process:

Absorption process:

Product layer

The rate is firstly dominated by the reaction on the surface and then by the diffusion in the product layer;

Desorption process:


Unreacted coreProduct layerDesorption process:

The rate is dominated by the reaction on the surface.

Absorption process:100

60

80

sion

x(%

)

0

20

40

Conv

ers

500℃ ex per i ment a l do t s 600℃ ex per i ment a l do t s 700℃ ex per i ment a l do t s 800℃ ex per i ment a l do t s 850℃ ex per i ment a l do t s

0 2 4 6 8 100

Ti me( mi n)

Absorption process Reaction dominated stage

1. The first stage is reaction dominated stage, which is rather fast; then slow down, change into product diffusion dominated stage.

2 In practical appliance the first stage is more crucial to the whole process


2. In practical appliance, the first stage is more crucial to the whole process thus should be more concerned.

Desorption process:p p

100

120缩核模型曲线

实验点

Theoretical data from SCM

Experimental data100

120 缩核模型曲线

实验点

Theoretical data from SCM

Experimental data

40

60

80

100%

80%

60%

nwer

sion

X (%

)

40

60

80

40%

30%

20%onw

ersi

on X

(%)

880 900 920 940 960 980

0

2040%

20%

Con

820 830 840 850 860 870 880 890 900 910 920 930 940 950 960

0

2010%

0%

Co

2

131

)(61t

tdtCeCkX

Temperature( ℃ ) Temperature( ℃ )

Temperature increases at a constant speed, which means T is a function of t. And C, Ce, K change with T, are not constant. So we can not directly calculate like previous process.


The theoretical and experimental lines fits quite well.

Research · Fixed-bed

25

O2 storage - various air flow rateAir

20

25

n (%

)

O Concentration

Φ:30mm

CoO:40gOxygen

Storage

10

15

2 con

cent

ratio

n

N 富积气体840

O2 Concentration g

20~40μm

g

0

5

O2 400ml/min Air

240ml/min Air

100ml/min Air

N2富积气体

800

820

atur

e (o C

)

400ml/min Air240ml/min Air100ml/min Air

00 20 40 60 80 100

Time (min)

Strong oxygen absorption capacity， 740

760

780

Tem

pera


g yg p p y，

Exothermic (heat release)740

0 20 40 60 80 100

Time (min)


35

O2 release - various temperatures CO2

（200mL/min）

25

30

35

o (%

)

1

2

At 920 , O2 concentration can last above 20% for a long time.

Considered the existent of vapour in flue th O t ti b

（200mL/min）

t1 > t2 > t3Oxygen

Release

10

15

20

O2 c

once

ntra

tino 2

3

9401

O2 Concentrationgas, the O2 concentration can be even higher after condensing the vapour.

O2、CO2

0

5

0 20 40 60 80 100900

920

erat

ure

(o C)

23

Time (min)

840

860

880

Tem

pe

Higher maximum O2 concentration is obtained with higher desorption temperature


8400 20 40 60 80 100

Time (min)

with higher desorption temperature

Endothermic


35

CO2O2 release - various CO2 flow rate

25

30

n (%

)

100ml/min CO2200ml/min CO2300ml/min CO2

Oxygen

Release

10

15

20

O2 c

once

ntra

tion

940

O2 Concentration O2、CO2

0

5

10

900

920

ratu

re (

o C)

O2 concentration decreases

0 20 40 60 80 100 120Time (min)

840

860

880

Tem

pe 100ml/min CO2200ml/min CO2300ml/min CO2


with increasing CO2 flow rate

Endothermic

0 20 40 60 80 100 120

Time (min)

Research · Dual fixed beds Preparation of the Co3O4/Al2CoO4 Oxygen Carrier Particle

① Activated alumina with particle size 200-450μm was selected and added into p μdistilled water.

② Cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was then also added into the mixture of distilled water and activated alumina.

③ This solution was stirred for 1 h at 348K and was dried at 353K for another 18 h before it was calcined at 773K for 3 h in air. By this method, water, and nitric acid in the solution could be evaporated off at different stages. Spherical particles were obtainedparticles were obtained.

④ These particles were calcined in air at 1,173 K for 1.5 h.⑤ Steps ②~④were repeated for 10-15 times until the mass ratio of Co3O4 to

Al2CoO4 was about 7/3.2CoO4 was about 7/3.

It was found from the results of XRD analysis that the synthesized Co-based oxygen carrier includes only Co3O4 and Al2CoO4


Co based oxygen carrier includes only Co3O4 and Al2CoO4.

Research · Dual fixed beds

1. Gas resource 2. Mass flow control unit 3. Four-way valve4. Fixed-bed reactor 5. Temperature control unit 6. Thermocouple7. O2 analyzer 8. Data acquisition

Parameters Temperature(℃)

Air flow rate(mL/min)

CO2 flow rate(mL/min)

Solid mass(g)

R t ⅠAbsor. process 600~850 1400 0

Ab t 250


Reactor Ⅰ About 250Desor. process 935 0 400

Reactor ⅡAbsor. process 600~850 1000 0

About 150Desor. process 925 0 400

40

50

60 氧气浓度曲线O2 concentration

10

20

30

40

0 100 200 300 400 500 600 700 8000

10

Time (min)

It is feasible to produce a continuous stream of oxygen-enriched carbon dioxide with oxygen concentration higher than 20%;Co-based O2 carrier has high cyclical stability.

700800900

10001100

re(℃

) t1 t2

温度曲线Temperature

100200300400500600

Temp

erat

ur


0 100 200 300 400 500 600 700 8000

100

Ti me ( mi n)

Research · Fluidized bed

25

O2 storage

15

20

%)

O2 Φ:30mm

Sample:236g

200 450 mOxygen

Storage

10

15

Conc

entra

tion

(%

Air(500mL/min)

200~450μm g

Temperature

700

800

9000

5

0 10 20 30 40 50 60 70 80800

100

200

300

400

500

600

t/ ℃

Time (min) 800

Similar with fixed bed.


0

100

0 10 20 30 40 50 60 70 80Time (min)


16

O2 release

10

12

14

%)

O2

Oxygen

Sample:236g200~450μm

4

6

8

Conc

entra

tion

(%

N (500mL/min )

Oxygen

Release

700

800

900

℃

0

2

0 20 40 60 80 100 120Time (min)

N2(500mL/min )

880

100

200

300

400

500

600

Tem

pera

ture

t/ ℃

Time (min)

Similar with fixed bed.


0

100

0 20 40 60 80 100 120Time (min)


16

O2 release and use @ 880

10

12

14

16

)

O2 CO2 CO SO2

Oxygen

Sample:236g200~450μm+P t l k 2 0

6

8

10

Conc

entra

tion

(%)

N2(500mL/min )

Oxygen

ReleasePetrol coke:2.0g200~450μm

600

700

800

900

℃

0

2

4

0 20 40 60 80 100 120 140 160

N2(500mL/min )

880

100

200

300

400

500

600

Tem

pera

ture

t/ ℃

Time (min)

The components of petrol coke used:


00 20 40 60 80 100 120 140 160

Time (min)

volatile content ：10.89%; fixed carbon ：89.11%.


35


25

30

%)

O2 CO2 CO SO2

Oxygen

Sample:236g200~450μm+P t l k 2 0

10

15

20

Conc

entra

tion

(%

N2(500mL/min )

Oxygen


700

800

900

℃

0

5

0 10 20 30 40 50 60 70

N2(500mL/min )

920

100

200

300

400

500

600

Tem

pera

ture

t/ ℃Time (min)


volatile content ：10 89%; fixed carbon ：89 11%


00 10 20 30 40 50 60 70

Time (min)



25


15

20

%)

O2 CO2 CO SO2

Oxygen

Sample:236g200~450μm+

10

15

Conc

entra

tion

(%

N (400mL/min )

Oxygen


700

800

9000

5

0 10 20 30 40 50 60 70 80 90Ti ( i )

N2(400mL/min )

900

200

300

400

500

600

700

Tem

pera

ture

t/ ℃

Time (min)




0

100

0 10 20 30 40 50 60 70 80 90Time (min)


Compare O2 release process with and without petrol coke:p 2 p p

a) The existence of petrol coke during the O2 release will keep O2concentration rather lower, especially at the beginning, this will increase the O2 release rate or decrease the required desorption temperature；

O i t h t th b i i d th CO t tib) O2 is even not enough at the beginning, and the CO concentration increases, the reaction rate is limited by the O2 release speed, higher rate achieves at higher temperature；

a) The sum of CO and CO2 will decrease to 0 finally, indicates the petrol coke were burnt completely at the end.


Summaryy Compared to perovskite-type materials, Co-based oxygen carrier solves the

problem of carbonation, has much higher oxygen capacity, reaction rate, p g yg p ycyclical stability;

Neither NO nor SO2 in the real flue gas will react with the Co-based oxygen carrier when using real flue gas as purge gas during the oxygen desorption g g p g g g yg pprocess;

It is feasible to produce a continuous stream of oxygen-enriched carbon dioxide with oxygen concentration higher than 20% using a Co-based oxygen yg g g ygcarrier packed in two parallel fixed-bed reactors operated in a cyclic manner;

Co-base oxygen carrier offers potential for O2-CO2 production using real flue gas as purge gas, which is applicable for the oxy-fuel coal combustion.g p g g , pp y

Petrol coke can be added and burned during the O2 release process. It can be burned completely, and the reaction rate is limited by the O2 release speed.


p

ACKNOWLEDGMENT

This work was supported by the National Natural Science Funds of China (No. (50806038) and the National Basic Research Program of China g(2006CB705807) .


Thank you for your attention!


kinetics study for o2 absorption/ desorption using a

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