kinetics study for o2 absorption/ desorption using a
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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
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Summary
IntroductionOxyfuel combustion — capturing CO2 from the use of fossil fuel
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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
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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%
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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
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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
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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
LSCFSCCFLMCFCMCFYBCt C
hang
e (%
)
2.02.53.03.54.0
LSCFSCCFLMCFCMCFYBCt C
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
LSCF SCCF LM CF CM CF
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.
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, 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
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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
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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 .
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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℃
700℃, Maxi mum r at e
405060708090
vers
ion
(%)
880℃850℃800℃700℃600℃
700℃, Maxi mum r at e
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.
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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
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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
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]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:
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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
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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.
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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
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g yg p p y,
Exothermic (heat release)740
0 20 40 60 80 100
Time (min)
Research · Fixed-bed
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
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8400 20 40 60 80 100
Time (min)
with higher desorption temperature
Endothermic
Research · Fixed-bed
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
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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
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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
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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
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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.
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0
100
0 10 20 30 40 50 60 70 80Time (min)
Research · Fluidized bed
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.
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0
100
0 20 40 60 80 100 120Time (min)
Research · Fluidized bed
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:
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00 20 40 60 80 100 120 140 160
Time (min)
volatile content :10.89%; fixed carbon :89.11%.
Research · Fluidized bed
35
O2 release and use @ 920
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
ReleasePetrol coke:2.0g200~450μm
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)
The components of petrol coke used:
volatile content :10 89%; fixed carbon :89 11%
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00 10 20 30 40 50 60 70
Time (min)
volatile content :10.89%; fixed carbon :89.11%.
Research · Fluidized bed
25
O2 release and use @ 900
15
20
%)
O2 CO2 CO SO2
Oxygen
Sample:236g200~450μm+
10
15
Conc
entra
tion
(%
N (400mL/min )
Oxygen
ReleasePetrol coke:2.0g200~450μm
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)
The components of petrol coke used:
volatile content :10.89%; fixed carbon :89.11%.
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0
100
0 10 20 30 40 50 60 70 80 90Time (min)
Research · Fluidized bed
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.
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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.
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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) .
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Thank you for your attention!
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