International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel combustion in BFB. Experiences and simulations
Luis M Romeo, Luis I Diez, Isabel Guedea, Irene Bolea Carlos Lupiañez, Pilar Lisbona, Yolanda Lara, Ana Martinez
CIRCE (Research Centre for Energy Resources and Consumption)
1
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
CIRCE
•
CIRCE
–
Non‐profit private organization, sponsored by the University of Zaragoza, the
Government of Aragón and Spanish industry
–
R&D in energy and thermal and electrical engineering, focus on efficiency and
renewable energy
–
Thermal division (~ 30 people):
•
Coal & biomass combustion, plant tests & monitoring, laboratory work, simulation,
CFD, conventional (PF) and advanced (FBC, IGCC, co‐firing) systems
•
CO2
capture: BFB Oxyfuel laboratory, Solid looping systems based on
CFB (mainly
Calcium looping) and studies about reduction of energy penalties
in CO2
capture
2
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
BFB Oxyfuel test rig
•
Test facility description–
90 kWt O2
/CO2
bubbling fluidized bed
–
2.5 m height, 20 cm i.d. FB water‐
cooled
–
2 x 200 litres hoppers for fuel feeding
(coal, sorbent, biomass)
–
CO2
/O2
mixer and flue gas
recirculation
–
Preheating of fluidising gas
–
Gas cleaning: settling chamber,
cyclone and fabric filter
–
Recycling ratio: from 0% to 60%
–
O2
in the mixture: from 20% to 60%
3
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
BFB Oxyfuel test rig
4
Preheating system/ Propane burner
Fuel feeder equipment
Air supply/ RFG
Gas supplyBubbling fluidized bed reactor
High efficiency cyclone
Heat exchangerFabric bag filter
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
•
First tests
–
Fluidization problems and control (pressure) of flue gas recirculation
–
SINTERING
•
Only in oxyfuel, maximum temperatures around 1000ºC
•
Bed agglomeration. Broken in small pieces
•
Bed sintering. Harder and larger than agglomerate.
5
Oxyfuel BFBC. Experimental
•
First tests
6
CaSO4Layer
O (15.2%)Ca (11.0%)Si (9.6%)K (3.0%)Al (4.5%)Fe (2.6%)
O (15.5%)Al (7.5%)Si (9.1%)Ca (9.4%)O (13.8%)
Si (21.2%)
2 mm
SEM3‐2
0
24
68
10
1214
16
O Na Mg Al Si S K Ca Ti Fe
SEM3‐1
02468
1012141618
O Na Mg Al Si S K Ca Ti Fe
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
7
Air Firing Ca/S= 2.5
CO2
/O2
= 65/35 –
60/40O2
= 3‐12% flue gases30 kW air 50‐70 kW oxy
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
8
Oxy FiringCa/S= 2.5CO2
/O2
= 65/35 –
60/40O2
= 3‐12% flue gases30 kW air 50‐70 kW oxy
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
•
SO2
emissions. Conclusions
–
As expected, in AF:
•
SO2
emissions increases with bed temperature (t > 830ºC)
•
Indirect sulfation
•
Sulfur capture remains around 90% with bed temp of 830‐860ºC
–
For OF
•
SO2
emissions are slightly higher than in AF
•
Sulfur capture remains near 90% with bed temperature of 860‐890ºC
•
Direct sulfation has been observed
•
Increasing bed temperature under OF conditions enhances SO2
capture, towards an
optimum temperature higher than in the case of air firing.
9
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
10
Air Firing
Oxy Firing
Ca/S= 2.5CO2
/O2
= 65/35 –
60/40O2
= 3‐12% flue gases30 kW air 50‐70 kW oxy
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
•
NOx emissions. Conclusions
–
As expected, in AF:
•
NOx concentration has showed a high dependence on O2
excess‐CO formed and coal
rank.
•
N‐fuel in lignite coal is lower than bituminous. This difference leads to lower NOx
emissions. Differences are shortened when expressed per energy unit
–
For OF
•
NOx concentration has showed a high dependence on O2
excess‐CO formed and
coal rank.
•
NOx concentrations has been clearly higher than under AF due to the large O2
concentration in comburent gas (35‐40% OF vs. 21% AF) and higher density of OF
exhaust gases
•
Differences are shortened when expressed per energy unit
11
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
•
Air in‐leakages in the facility during
oxy‐firing tests is detected: 7‐8 %, up to 15‐20% with RFG
•
NOx
concentrations are higher under
oxy‐firing conditions
•
CO2
concentrations in oxy‐firing cases are around 90% (d.b)
•
Combustion efficiencies are around 95 %
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Romeo et al. 2011. Experimental Thermal and Fluid Science 35 (2011) 477–484
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
•
This ‘‘D‐shape’’
profile is explained by the increase of
heat rates due to char combustion located near the
splash zone
•
A different distribution of heat release in the
combustor, between the bed and the free‐board is
obtained with biomass: volatiles released from the
biomass are not completely burned in the dense‐solid
zone
13
Romeo et al. 2011. Experimental Thermal and Fluid Science 35 (2011) 477–484
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
•
Lower minimum fluidization velocities
values where detected under O2
/CO2
mixtures
•
The increase of the CO2
concentration in the
mixture brings along a increase of the bed
porosity
•
Pressure drop through the distributor change with
different gases blends: importance of the design
14
Guedea et al. /2011. Chemical Engineering Journal doi:10.1016/j.cej.2011.10.026
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC. Experimental
–
Low primary fragmentation was detected for both sort
of limestone
–
Oxy‐firing decreases primary fragmentation likely due
to the absence of calcination
–
Other parameters as particle size or SO2
concentration
do not seem to affect primary fragmentation
–
Limestone particle size distribution models under air‐
firing can be simplified to be used in oxy‐firing case
15
C. Lupiáñez et al. 2011. Fuel Processing Technology, 92, 1449–1456
PRIMARY FRAGMENTATION UNDER OXY‐FIRING CONDITIONSIn collaboration with Consiglio Nazionale delle Ricerche CNR,
and Università
di Napoli Federico II
Thermal shockGas releasing (steam and CO2
)Effective particle size Original particle size
Atmosphere compositionTemperatureLimestone
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC‐CFBC. Simulation
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O2
+CO2
denser
than O2
+ N2
Higher O2
concentration
More compact boilers↓
Less available area for water
wall heat exchanger
Higher particle combustion
temperature
Need of additional heat transfer for controlling bed temperature
More intensity in transfering heat to
the available water wallsHigher transfer in the External
Heat Exchanger
By increasing Gs
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel BFBC‐CFBC. Simulation
•
1.5D large‐scale CFB simulation:
–
From air to oxy, boiler size may
reduce up to 35% and recoverable
heat in EHE increases 15 points
–
For certain boiler size: higher Gs
and thus, EHE heat transfer, allows
wider range of power loads.
–
EITHER increasing Gs OR cooling
solids further ‐> EHE is essential
–
Conventionally EHE consists of a
BFB but…how will it fluidized? ‐>
proper conditions for re‐
carbonation of CaO
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Oxyfuel CFBC. Simulation
–
Solid looping systems
•
Solid looping systems
–
650ºC at carbonator, exothermic reaction
–
925ºC at calciner, pure CO2
•
Additional fuel input and O2
necessities
•
Four sources of high temperature heat
–
Many integration schemes with supercritical steam
power plants
•
Very competitive CO2
avoided cost, lower than 15
€/tCO2
–
Cheaper sorbents for low quality fuels (high ash
and sulphur content)
–
Expensive sorbents for high quality fuels (low ash
and natural gas)
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Romeo et al. 2009. Chemical Engineering Journal, 147, 252–258
Romeo et al. 2008. Energy Conversion and Management 49, 2809–2814
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel CFBC. Simulation
–
Solid looping systems
Lisbona et al. 2010. Energy Fuels, 24, 728–736
19
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Oxyfuel CFBC. Simulation
CLC EXERGETIC ANALYSIS
•Coal Thermal input : 550 MWth
•Net power output: 279.8 MWe
–
High efficiency CLC with coal as fuel
(50.9%) (CO2
compression included)•
Steam turbine output, 119.8 (MWe
)•
Gas turbine output, 156.9 (MWe
)•
CO2
turbine output, 47.7 (MWe
)•
CO2
compression, 29.9 (MWe
)•
Net power output, 279.8 (MWe
)
–
Exergy efficiency was 64.2%•
The highest irreversibility was located in
the reactors (83.9 MW)
•
Lowest exergy efficiency in CO2
heat
exchangers (66.25%)
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Guedea et al. 2011. International Journal of Energy and Environmental Engineering, 2, 35‐47
International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, November 2011
Conclusions. Future work
•
On‐going experimental tests in oxy BFB–
High oxygen concentration, sulphur in coal, temperatures
–
Recirculation and secondary comburent
–
Coals and co‐firing with biomass
•
The role of EHE. Recarbonation. Influence in design
•
Opportunities for energy penalty reduction in CO2
captures based on FB–
Oxyfuel combustion
–
Looping systems
–
Chemical looping combustion
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International Energy Agency ‐
Fluidized Bed Conversion
Ponferrada, 29‐30 November 2011
Oxyfuel combustion in BFB. Experiences and simulations
Acknowledgements
R+D Spanish National Program from the Spanish Ministry of Science and Innovation (MICINN, Ministerio de Ciencia e
Innovación): projects ENE2005‐03286/ALT, ENE2008‐00440, ENE‐2009‐08246, CIT‐440000‐2009‐26.
Fundación CIUDEN is also acknowledged for the support to the oxyfuel rig development
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