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EVALUATION OF
DIRECT COAL CLC PROCESSES
A. Abad, P. Gayán, A. Cuadrat, I. Adánez-RubioL. F. de Diego, F. García-Labiano, J. Adánez
Instituto de Carboquímica (ICB-CSIC), Dept. of Energy & Environment, Zaragoza, Spain
VIENNA, 30th-31st August 2011
3rd High Temperature Solid Looping Network Meeting
A. Gasification of coal in the fuel-reactor
B. CLOU: Chemical-Looping with Oxygen Uncoupling
Introduction
Coal
CO2 + H2ON2 (+O2)
MexOy
H2O(l)
CO2
Air Reactor
FuelReactor
MexOy-1
Condenser
Air
CLC: Direct coal feeding to the fuel-reactor
H2O(v)and/or
CO2Ash
Two options to evaluate
CO2
A. Gasification of coal in the fuel-reactor
Coal
H2O and/or CO2
H2O
CO H2
H2O
Char
Volatiles
Oxygen-Carrier
CO2 H2O
First, coal is dried and devolatized
Remaining solid char is gasified to give gaseous H2and CO
Volatiles and Gasification Products react with oxygen-carrier as a gas-solid reaction
► Coal H2O + Volatile matter + Char
► Char + H2O H2 + CO
► Char + CO2 2 CO
► + n MexOy CO2 + H2O + n MexOy-1Volatile matter
H2 + CO
H2OCO2
Introduction
B. CLOU(*): Chemical-Looping with Oxygen Uncoupling
Here, coal is also dried and devolatized
But the oxygen-carrier is able to release gaseous OXYGEN (O2)
Volatiles and Char react with OXYGEN (O2) as in common combustion with air
► Coal H2O + Volatile matter + Char
► + O2 CO2 + H2OVolatile matter
Char
Coal
O2
CO2 H2O
Volatiles
CO2
CO2
Char
CO2 H2O
Oxygen-Carrier
► 2 MexOy 2 MexOy-1 + O2
Introduction
(*) T. Mattisson, A. Lyngfelt, H. Leion. Int J Greenhouse Gas Control, 2009, 3, 11-19
Key properties of Oxygen-Carriers for CLC with coal
Gasification in the fuel-reactor
• Natural ores
• Waste materials
CLOU
Reactivity is not a key factor, because gasification is a slow reaction
Low cost material are very interesting
Introduction
Temperature (ºC)600 800 1000 1200
Part
ial p
ress
ure
of O
2 (at
m)
0.01
0.1
1
CuO/Cu2OMn2O3/Mn3O4
Co3O4/CoO
Appropriate thermodynamic for oxygen uncoupling at temperature of interest
Objective
Evaluate the key aspects for a good performance of CLC and CLOU with coal
CLC and CLOU experiments were carried out in a continuously operated unit.
A comparison between these options was carried out by analyzing:
• Carbon capture efficiency
• Combustion efficiency
CSIC-ICB-s1 rig for CLC and CLOU with coalConfiguration CLC CLOU
Oxygen-Carrier Ilmenite Cu60MgAl
Preparation method Natural ore Spray-drying
Oxygen capacity (%) 4 6
Particle size (µm) 150-300 100-200
Solids in Fuel-reactor ~ 800 g ~ 450 g
Total solids 3500 g 2000 g
Fuel (200-300 µm) “El Cerrejón” coal “El Cerrejón” coal
Fluidization gas FR H2O N2/CO2
1.- Fuel Reactor (i.d. 5 cm)Bed height: 20 cm
2.- Loop seal 3.- Air Reactor (i.d. 8 cm)
Bed height: 10 cm 4.- Riser5.- Cyclone
6.- Diverting solids valve7.- Control solids valve8.- Coal9.- Screw feeders10.- Furnaces11.- Vaporizer12.- Tar recovery
Experimental
H2O CO2 N2N2Air
Sec.Air
7
82
4
5
6
10
3
1
9
1110
AIR REACTOR
FUEL REACTOR
H2O CO2 N2N2Air
Sec.Air
7
82
4
5
6
10
3
1
9
1110
AIR REACTOR
FUEL REACTOR
Gas analysisO2, CO, CO2
Tar analysisGC – MS
Stack
StackAir
Stack
Gascombustion
Tar recovery
10
Gas analysisCH4, CO2, CO, H2
12
Coal or biomass
H2O CO2 N2N2Air
Sec.Air
7
82
4
5
6
10
3
1
9
1110
AIR REACTOR
FUEL REACTOR
H2O CO2 N2N2Air
Sec.Air
7
82
4
5
6
10
3
1
9
1110
AIR REACTOR
FUEL REACTOR
Gas analysisO2, CO, CO2
Tar analysisGC – MS
Stack
StackAir
Stack
Gascombustion
Tar recovery
10
Gas analysisCH4, CO2, CO, H2
12
Coal or biomass
Experimental planning
Exp.Type
Fuel Reactor Temperature
(ºC)
Coal Feed (g/h)
FuelPower(Wth)
SolidsInventory
(kg/MWth)
SolidsFlow
(kg/h)
tres Solids in FR (min)
Fluid. Gas
CLC 880-950 42 250 3200 3.5 13 100% H2O
CLC 890 42 250 3200 1.6-11 4-30 100% H2O
CLOU 900-960 112 700 600 4.5 6 N2
CLOU 900 112 700 600 4-14 2-7 N2
CLOU 925 67-256 400-1500 240-1150 9.0 3 N2
Experimental
Performance evaluation
Carbon capture efficiency
Char conversion
Combustion efficiency in the Fuel Reactor
Carbon converted to gas in the FREff.CC =Carbon introduced
Ox. supplied by oxygen carrierEff.Comb FR=Ox. demand coal converted in fuel reactor
charC in char converted in the FRX =
C in char introduced
COAL
Coal conversion
CO2
H2O
FuelReactor
Un-burnt products
(CH4+CO+H2)
Air
CO2
CHAR
Eff.Comb FR
Eff.CC
N2
AirReactor
Experimental
Effect of the Fuel Reactor Temperature
Con
cent
ratio
n,dr
y, N
2 fre
e (%
)
0
20
40
60
80
Tem
pera
ture
(ºC
)
800
840
880
920
960
T
CO2
CH4
H2CO
time (h)0 1 2 3 4 5
Con
cent
ratio
n (%
)
0369
121518
AIR REACTOR
O2
FUEL REACTOR
CO2
Results CLCOC: Ilmenite
• Smooth operation
• Full combustion was not reached
• No tars nor other hydrocarbon that CH4
► Un-burnt gases only coming from volatiles
Temperature (ºC)860 880 900 920 940 960
Cha
r con
vers
ion
(-)0.0
0.2
0.4
0.6
0.8
1.0
Temperature (ºC)860 880 900 920 940 960
Effic
ienc
y (%
)
0
20
40
60
80
100
Results CLCOC: Ilmenite
► Carbon Capture & Combustion Efficiency
► Char conversion
Carbon Capture Eff.
Combustion Eff.
Effect of the Fuel Reactor Temperature
Carbon capture increases due to enhanced gasification rate
High temperature (likely >1000 ºC) to get high char conversion and carbon capture
Combustion efficiency: Volatile matter is better burnt at higher temperature
3200 kg/MWth
tres = 13 min
Residence time (min)0 10 20 30 40
Effic
ienc
y (%
)
0
20
40
60
80
100
Carbon Capture Eff.
Combustion Eff.
Residence time (min)0 10 20 30 40
Cha
r con
vers
ion
(-)0.0
0.2
0.4
0.6
0.8
1.0
Results CLCOC: Ilmenite
► Carbon Capture & Combustion Efficiency
► Char conversion
Effect of the Average Residence Time
Carbon Capture increases with residence time because of higher char conversion
Combustion efficiency barely affected by residence time of solids
3200 kg/MWth
TFR = 890 ºC
Effect of the Fuel Reactor Temperature
Results CLOUOC: Cu60AlMg
• Smooth operation
• Full combustion was always reached
• Very low concentration of CO2 from the air reactor
860880900920940960980
0
10
20
30
40
50
time (min)0 50 100 150 200 250 300
860
880
900
920
940
0
10
20
FR
AR
T
T
CO2
O2
CO2
O2
Tem
pera
ture
(ºC
)
CO
2or
O2
(vol
.%)
► Oxygen (O2) appears together combustion gases at equilibrium for CuO/Cu2O
Temperature (ºC)900 920 940 960
Cha
r con
vers
ion
(-)0.90
0.92
0.94
0.96
0.98
1.00
Temperature (ºC)900 920 940 960
Effic
ienc
y (%
)
90
92
94
96
98
100
► Carbon Capture & Combustion Efficiency
► Char conversion
Carbon Capture Eff.
Combustion Eff.
Results CLOUOC: Cu60AlMgEffect of the Fuel Reactor Temperature
Very high Carbon Capture efficiencies were found
Char conversion in FR increases with the temperature
Complete combustion in the fuel reactor is reached
600 kg/MWth
tres = 6 min
Residence time (min)0 2 4 6 8 10 12 14
Cha
r con
vers
ion
(-)0.80
0.85
0.90
0.95
1.00
Residence time (min)0 2 4 6 8 10 12 14
Effic
ienc
y (%
)
80
85
90
95
100
► Carbon Capture & Combustion Efficiency
► Char conversion
Carbon Capture Eff.
Combustion Eff.
Results CLOUOC: Cu60AlMgEffect of the Average Residence Time
Carbon Capture increases with residence time because of higher char conversion
Combustion efficiency: always complete combustion was observed
600 kg/MWth
TFR = 900 ºC
Solids inventory (kg/MWth)0 250 500 750 1000 1250
Cha
r con
vers
ion
(-)0.80
0.85
0.90
0.95
1.00
Solids inventory (kg/MWth)0 250 500 750 1000 1250
Effic
ienc
y (%
)
90
92
94
96
98
100
► Carbon Capture & Combustion Efficiency
Carbon Capture Eff.
Combustion Eff.
Results CLOUOC: Cu60AlMgEffect of the solids inventory
Carbon Capture and Combustion efficiency not affected for solids inventory decreasing from 1150 to 240 kg/MWth
Full combustion of coal was observed even at the lower solids inventory Lower oxygen-carrier inventories could be attained with full combustion
► Char conversionTFR = 925 ºC
tres=3 min
Temperature (ºC)900 920 940 960 980
Rat
e of
cha
r con
vers
ion
(%/s
)0.1
1
10
100
Temperature (ºC)880 900 920 940 960
Effic
ienc
y (%
)
0
20
40
60
80
100
60 times higher
with CLOU
► Char conversion rate► Carbon capture
CLC
CLOU
CLC
CLOU
Comparison CLC & CLOU
Comparison CLC & CLOU
Temperature (ºC)880 900 920 940 960
Effic
ienc
y (%
)
80
85
90
95
100
► Combustion efficiency
CLC
CLOU • Better combustion in CLOU
• Low combustion efficiency in CLC is not justified by reactivity of ilmenite
• The contact between volatiles and oxidant agent is relevant for good combustion
• Requirement of a carbon separation system to reach high carbon capture
Conclusions
► CLC
Key aspects
► CLOU
• Very high carbon capture efficiency can be reached without a carbon separation system
• To obtain complete gas combustion an improved design of the fuel reactor or/and an oxygen polishing step should be used
• An oxygen polishing step is not necesary because full gas combustion can be reached with low solids inventory
• A low cost material (e.g. ilmenite) can be used as oxygen carrier
• To optimize the cost of the oxygen carrier in the CLOU process considering a long live and/or a low costSeparation from ashes is a key factor
Coal
CO2 + H2ON2 (+O2)
Air Reactor
FuelReactor
AirH2O(v)and/or
CO2AshAsh
Char
C separationsystem
Coal
CO2 + H2ON2 (+O2)
Air Reactor
FuelReactor
AirH2O(v)and/or
CO2AshAsh
Char
C separationsystem
• Requirement of a carbon separation system to reach high carbon capture
Conclusions
► CLC
Key aspects
► CLOU
• Very high carbon capture efficiency can be reached without a carbon separation system
• To obtain complete gas combustion an improved design of the fuel reactor or/and an oxygen polishing step should be used
• An oxygen polishing step is not necessary because full gas combustion can be reached with low solids inventory
• A low cost material (e.g. ilmenite) can be used as oxygen carrier
• To optimize the cost of the oxygen carrier in the CLOU process considering a long live and/or a low costSeparation from ashes is a key factor
EVALUATION OF
DIRECT COAL CLC PROCESSES
VIENNA, 30th-31st August 2011
3rd High Temperature Solid Looping Network Meeting
THANK YOU!A. Abad, P. Gayán, A. Cuadrat, I. Adánez-Rubio
L. F. de Diego, F. García-Labiano, J. Adánez
