CO 2 Capture from Gasification Syngas via Cyclic Carbonation / Calcination Robert Symonds,...
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Transcript of CO 2 Capture from Gasification Syngas via Cyclic Carbonation / Calcination Robert Symonds,...
CO2 Capture from Gasification Syngas
via Cyclic Carbonation / Calcination
Robert Symonds, University of Ottawa
SupervisorsDr. A. MacchiDr. E. J. Anthony
Robin HughesCANMETNRCan
Overview
Introduction• Hydrogen production in Canadian context
Objectives
Experimental Method
Results• Kinetic parameters
• Sorbent decay
• Morphology
• Observations
Operational CANMET pilot facilities for CO2 looping studies
Summer 2008 Testing
Introduction - Gasification
In Canada, very large quantities of H2 will be produced via gasification for heavy and ultra heavy oil upgrading, power production, and possibly transportation
• The production of syngas (mainly CO and H2) from a number of carbonaceous fuel sources including coal, petroleum coke, oil, asphaltenes, and biomass occurs via:
3C + O2 + H2O -> 3CO + H2
• The syngas can be shifted to hydrogen via the water-gas shift reaction in the presence of steam
CO + H2O -> CO2 + H2
• The production of hydrogen via gasification results in high CO2 emissions unless the CO2 can be sequestered
Oil Sands – Need low cost hydrogen Production and upgrading facilities are expected to grow by a factor of 5 over the next 25 years. Aggregate Production Forecast:2003 – 1.1 million b/d 2012 – 2.0 million b/d 2030 – 5.0 million b/d
• Natural gas price is volatile and supply will diminish;
• Will need alternative fuels (coal, petroleum coke and refinery residues) to meet the demand; however,
• Higher carbon fuels will increase CO2 emissions
H2 Production for Oil Sands using Gasification
H2 Production Comparison
• CO2 emissions are increased when producing H2 from asphaltenes and pet coke when compared to natural gas
• If 90% CO2 capture with gasification assumed then emissions are less than SMR with natural gas
• Gasification for hydrogen with CO2 capture and compression (ex. 150 bar) is less energy intensive and more cost effective
W/O CO2 Capture W/ 90% CO2 CaptureSource: White 2007, Air Products
CO2 emission, tonne/kNm3 H2
SMR, NG 0.9
Asphaltene gasification 1.3
Pet coke gasification 1.8
CO2 emission, tonne/kNm3 H2
SMR, NG 0.37
Asphaltene gasification 0.17
Pet coke gasification 0.19
Canadian Gasification with CCS
EPCOR - 90% CO2 capture• Genesee 4 – 500 MW coal IGCC for electrical
power production• Front end engineering design underway• FEED funding industrial/provincial/federal• 8000 TPD coal
Sherritt – ~4.5 Mt/yr CO2• Dodds-Roundhill – 270 MSCFD hydrogen
production via coal gasification• Hydrogen to be used for oil sands upgrading
Opti-Nexen – Long Lake project• Oil sands operator producing very high quality
synthetic crude oil• Gasifying asphaltenes for H2, steam, and
power• Phase I includes 4 Shell gasifiers
Introduction - CO2 Sorbents
Investigating methods for syngas CO2 separation that can be performed at high temperature and pressure• Metal oxides have high equilibrium capacities. • Can generate a nearly pure stream of CO2 (>85 %) needed for
sequestration
Objectives
• Determine the effect of ‘slagging gasifier’ syngas on carbonation reaction kinetics for naturally occurring calcium oxide based sorbents.
• Determine reaction kinetics for the development of a single phase, plug flow, moving bed carbonator reactor model.
• Perform sensitivity / parametric analysis of carbonator reactor model.
Experimental Equipment – TGA
Measurement Techniques – Limestone
)0()(
)0()(
3 CaOCaCO
CaOCaO
mmpurity
mtmX
−⋅−
=
13
15
17
19
21
23
25
0 1000 2000 3000 4000 5000
Time (s)
0
100
200
300
400
500
600
700
800
900
Experimental Conditions
Naturally occurring calcium oxide based sorbents• Havelock Limestone• Newfoundland Dolomite
Particle size range• 250 – 425 micron
0.20 0.06 42.99
0.17 1.30 21.25 30.51 0.15 0.04 44.40
0.34 0.30 0.29 54.10Havelock
Newfoundland Dolomite
1.90
2.12
Sorbent SiO 2 Al2O3 Fe 2O3 MgO CaO Na 2O K2O LOI
Experimental Conditions
Feed Gas – Carbonation• GE gasifier with Illinois bituminous coal as a feed (Simbeck et al., 1993)• CH4, H2S, NH3, and HCN have been omitted from the syngas feed stream
With CO and H2
Without CO and H2 0 0 0.17 0.75
H2O N2
0.08
0.08
0.42 0.21 0.17 0.12
CO2 CO H2Carbonation Feed Gas
Experimental Conditions
Temperature – Carbonation • 580, 620, 660, 700oC
Feed Gas – Calcination• N2
• CO2 and N2 (similar to Abanades et al., 2003)
Temperature - Calcination• 850 and 915oC
Atmospheric pressure, 10 cycles
Rate of Reaction
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 100 200 300 400 500 600
Time (s)
(1-(1-X)
1/3
)
With CO and H2
Without CO and H2
Reaction rate given bymaximum slope for grainmodel
Effect of Carbonation Feed Gas
• Presence of CO/H2 have increased the initial rate of carbonation by 70%
• Increased local CO2 concentration at CaO surface?
• Believe CaO or an impurity may be catalyzing the water-gas shift reaction• Calculated activation energies are 60.3 and 29.7 kJ/mol with and without the
presence of CO and H2 during carbonation
• Sun et al. (2008) determined activation energy was 29 ± 4 kJ/mol without CO/H2
ks (mol/m2.s.kPa)
620 0.0029 1.29E-06
Feed Gas Composition (vol%)
Total Pressure (atm) Temperature (oC) r0 (1/s)
8 CO 2, 21 H 2, 42 CO,
17 H2O, 12 N 2
8 CO 2, 17 H 2O, 75 N 2
1
1 620 0.0017 7.58E-07
Sorbent Decay
• Presence of CO and H2 during the carbonation of Havelock particles have little impact on the CaO conversion over 10 cycles
• Expected since particle sintering should be similar based on identical calcination conditions, but sorbent morphology indicates physical differences
fw
0.328
0.3248 CO 2, 17 H 2O, 75 N 2 1 620 0.74910
Temperature (oC) fm
8 CO 2, 21 H 2, 42 CO,
17 H2O, 12 N 21 620 0.749
N Cylces
10
Feed Gas Composition (vol%)
Total Pressure (atm)
Sorbent Decay - Gas Composition
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 1 2 3 4 5 6 7 8 9 10
Cycle
Conversion
Without H2 and CO
With H2 and CO
TG850/0
Best Fit
Presence of Steam
• The presence of steam increases the carbonation conversion by approximately 30% at the end of the 10th cycle
• Several authors (Lin et al., 2005 and Gupta et al., 2002) observed a significant increase in CaO conversion via the intermediate formation of Ca(OH)2 but neither these processes lie within the carbonation conditions explored in this work
• In a recent study on sulphation under oxy-fired conditions evidence was advanced for the transient formation of Ca(OH)2, with an effect on carbonation (Wang et al., 2008)
• The addition of steam seems to result in the creation of larger pores
Sorbent Decay - Temperature
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 1 2 3 4 5 6 7 8 9 10
Cycle
Conversion
580oC
620oC
660oC
700oC
250-425 micron Havelock calcined at 850 C with N2, carbonated with 8% CO2, 21% H2, 42% CO, 17% H2O, and 12% N2
Sorbent Morphology
Calcined at 850 C with N2 and carbonated at 580 C with 8% CO2, 17% H2O, and 75% N2
Calcined at 850 C with N2 and carbonated at 580 C with 8% CO2, 21% H2, 42% CO, 17% H2O, and 12% N2
After 10 cycles of calcination/carbonation
Sorbent Morphology
Calcined at 850 C with N2 and carbonated at 580 C with 8% CO2, 17% H2O, and 75% N2
Calcined at 850 C with N2 and carbonated at 580 C with 8% CO2, 21% H2, 42% CO, 17% H2O, and 12% N2
After 10 cycles of calcination/carbonation
Calcination
• Under a 90% percent atmosphere of CO2, the initial rate of carbonation is 1/5 that of calcination with pure N2.
• It is known that during sintering, necks develop between adjacent micrograins and continue to grow. The material for this is supplied from the rest of the micrograin, so that the distance between grain centers is diminished. This causes both the voidage and the surface area to decrease (Stanmore and Gilot, 2005).
2.23E-06
ks (mol/m2.s.kPa)
4.91E-07
100 N2 1 915 0.0050
90 CO 2, 10 N 2 1 915 0.0011
Feed Gas Composition (vol%)
Total Pressure (atm) Temperature (oC) r0 (1/s)
Sorbent Morphology
• Images after first calcination/carbonation cycle• Calcined at 915 C and carbonated at 620 C with 8% CO2, 21%
H2, 42% CO, 17% H2O, and 12% N2
Calcined under N2; kept under CO2 until temperature ready for calcine
Calcined under 90% CO2; balance N2
CO2 Looping Cycle Pilot Plant
Sorbent
Flue Gas
Fuel
FreshLoadedRegenerated
CoalCoke
AirOxygen
Low CO2 (< 5%)High CO2 (~92%)
Oxidant Oxy-Fuel CFB
Calciner
Air Blown Combustor
Carbonator
Our small oxy-fuel CFBC
Current Configuration• 5 m in height, 0.1 m ID
• 18 kW of electric heaters surrounding dense bed region
• Primary and secondary oxidant ports with flue gas dilution
• Independent fuel and sorbent injection
• Recycle system includes condenser, condensate KO, and blower
• Utilities include steam, water & air
• Fluidizing gas 65+ mol% O2
• BFB or CFB
Oxy-Fired Circulating Fluidized Bed (CFB)
• 10 m; 0.6 m ID• Maximum oxygen flow
250 kg/hr• Currently set up for a
maximum oxygen concentration of 27 mol%
• 1 m BFB adjacent with solids transport lines
• BFB opeated as a gasifier or combustor
• Previously operated as an Exxon style fluid bed coker (5 years)
• Proposal submitted for CO2 looping in this facility
Effect of Hydration
0 10 20
Cycle Number
0.0
0.2
0.4
0.6
0.8
1.0
Conversion, X
N
• Hydrated Cadomin limestone derived sorbent conversion to CaCO3 at various conditions
• Conversion as high as 0.57 after 20 cycles
• Sorbent was likely too friable for commercialization
• No SO2 in sample gases
• Calcined in N2
Sorbent Pelletization
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 1 2 3
Crushed, 600-1400 micronPowder, 25-100 micronPellet, Binder: WaterPellet, Binder: Water & 5% Na2CO3Pellet, Binder: Water & Na BentonitePellet, Binder: Water & Ca Bentonite
Conversion
Cycle Number
Pilot Scale Work Summer 2008
Objective• Investigate CO2 capture processes at pilot scale under
atmospheric pressure; flue gas & syngas
Experimental equipment• Batch or continuous operations in 0.1 m ID fluidized
beds• Calcine with oxy-fired wood pellets with recycled flue
gas (dry recycle, O2 up to 65 mol%)• Carbonate with mildly fluidized or moving bed gas
velocities• Rotary tube furnace
• Pretreatment or periodic treatment• Max 1400 C; 21 kW• 1 m heated length; 1 - 5 rpm• Can add steam etc. to heated zone
Early results• Tests to date with air/CO2/H2O• Steam allowing CO2 capture at equilibrium levels even
below 580 C
Results and Discussion – Comparison of Calcium Oxide based Sorbents
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 2 3 4 5 6 7 8 9 10
Cycle
Conversion
Limestone
Dolomite
Results and Discussion – Naturally Occurring Dolomite
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 1 2 3 4 5 6 7 8 9 10
Cycle
Conversion
Without CO and H2
With CO and H2
Results and Discussion – Comparison of Calcium Oxide based Sorbents
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
1 10 100 1000
Pore Diameter (nm)
Pore Volume (cm
3/g.nm) Havelock
N. Dolomite
Carbonation Temp Havelock Limestone
y = -7254.5x - 5.54
R2 = 0.9688
-14.2
-14.0
-13.8
-13.6
-13.4
-13.2
-13.0
-12.8
0.001 0.00104 0.00108 0.00112 0.00116 0.0012
1/T (1/K)
ln(k
s)