design considerations for direct solid fuel chemical looping combustion … · 2013. 7. 25. ·...
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Institute of Chemical EngineeringResearch Group Future Energy Technology
Prof. Hermann Hofbauer
Getreidemarkt 9/166 1060 Wien
www.vt.tuwien.ac.at
Design considerations for direct solid fuel chemical looping combustion systems
Tobias Pröll, Johannes Schmid, Christoph Pfeifer and Hermann Hofbauer
IEA GHG R&D ProgrammeHigh Temperature Solid Looping Cycles Network
2nd Network Meeting, Alkmaar, September 15-17, 2010
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 2T. Pröll
Outline
What is chemical looping combustion (CLC)?
CLC for gaseous fuels – status and limitations
CLC for solid fuels – challenges and approaches
Excursion: dual bed biomass gasification
Improved dual circulating fluidized bed design
Conclusion and outlook
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 3T. Pröll
Chemical looping combustion (CLC)
A new process for oxidizing fuels using metal oxides as oxygen carriers transporting oxygen from combustion air to fuel
No mixing of combustion air and fuel, combustion products (CO2 and H2O) not diluted by N2
Highly exothermal reactions in air reactor
Global heat release equal to that of direct combustion
Air reactor(AR)
Fuel reactor(FR)
MeOx
MeOx-1
Air
N2, (O2)CO2, (H2O)
Fuel
Cooling/ condensation
CO2
H2O
CLC shows unique potential for carbon capture because gas-gas separation is inherently avoided.
Global air/fuelratio > 1
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 4T. Pröll
Critical issues in CLC
Oxygen carrier particles• thermodynamic suitability• high reactivity• sufficient transport capacity• high mechanical stability• cyclic stability of reactivity and transport capacity
Reactor system• excellent gas-solids contact in both reactors• sufficient solids circulation rate
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 5T. Pröll
Dual fluidized bed systems
High in both reactors, no gas phase conversion without solids
Oxygen and heat transportChemical looping
High in the absorber/carbonator, low in the re-calciner (heat-driven)
CO2 (and heat) transportCarbonate looping for
CO2 capture
High in the reformer/carbonator, low in the re-calciner (heat-driven)
CO2 and heat transport, catalyst
Sorption enhanced reforming
Partially for tar reforming in the gas generatorHeat transport, catalyst(Biomass) gasification
Importance of gas–solid contactPurpose of solidsTechnology
Dual fluidized bed technologies apart from FCC
There is an ultimate requirement for good gas-solid contact in CLC systems
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 6T. Pröll
Dual circulating fluidized bed(DCFB) reactor system
• Global solids circulation is controlled by air reactor fluidization only (eg. air staging)
• Fuel reactor can be optimized towards fuel conversion
• Inherent stabilization of global solids hold up due to the direct hydraulic link between the reactors
• Low reactor volume compared to bubbling fluidized beds (i.e. low specific solids inventory)
• High potential for scale-upai
rrea
ctor
(AR
)
exhaustAR
fuel
reac
tor(
FR)
exhaustFR
air fuel
LS
LS
LS
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 7T. Pröll
CLC pilot plant
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 8T. Pröll
Status CLC for gaseuos fuels
140 kW DCFB pilot plant / NiO-based oxygen carrier:• CH4 conversion up to 99% • CO2 yield up to 96% based on total carbon in fuel• good fuel conversion in spite of the limited riser heights
Scale up to next size of about 10 MW possible
Immidiate application for industrial steam generation
Potential for power production limited because of competing gas turbine combined cycle technology
Two development targets for efficient power production• direct use of solid fuel – steam cycle application• pressurized operation for combined cycle application
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 9T. Pröll
CLC for solid fuels
There is a huge potential in CLC for coal
There is a lot of recent research on this topic
There are three main challenges associated with direct solid fuel introduction:
• decomposition and oxidation of volatile compounds• satisfactory conversion of char in the fuel reactor• selective removal of fuel ash from the system
Two of the challenges address fuel reactor design
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 10T. Pröll
Problem definition
Volatiles form bubbles and move quickly upwards lowcontact time to oxygen carrier
→ Force gas phase to pass dense regions before leavingthe system
Solids are well mixedimmediate loss of unreactedchar to air reactor
→ Try to obtain tubular reactorlike solids flow behavior or
→ Selectively separate carbonfrom oxygen carrier
airr
eact
or(A
R)
fuelreactor(FR)
LS
LS
airsteam
exhaustAR
exhaustFR
solid fuel
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 11T. Pröll
Theoretical consideration
Fuelreactor
MeOxMeOx
MeO(x-1)MeO(x-1)
CondensationDepleted airDepleted air
(to compression)(to compression)
Air reactorAir reactor
QAR.QAR.
global air ratio > 1global air ratio > 1CO2 + H2O CO2
H2O
Solid fuel
Air Steam
endoxidizer
devola-tizer
chargasifier
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 12T. Pröll
Early design proposal
from: Lewis W.K., Gilliland E.R. Production of pure carbon dioxide. U.S. Patent No. 2,665,972, 1954.
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 13T. Pröll
Early design proposal (2)
from: Lewis W.K., Gilliland E.R. Production of pure carbon dioxide. U.S. Patent No. 2,665,972, 1954.
solid fuel
If solid fuel is introducedbetween the "stages":
volatiles must pass through zones above
char is led along with bedmaterial through zonesbelow
Problems: too complicatedgeometry to be built at large scale, high pressure drop
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 14T. Pröll
Dual fluidized bedgasifier technology
producer gas flue gas
biomass
steam air
riser
gasifier
connecting chute
additional fuel
loop seal
producer gas flue gas
biomass
steam air
riser
gasifier
connecting chute
additional fuel
loop seal
additional fuel
loop seal
History:→Experience at Vienna
Univ. of Technol. since1993
→ 3rd generation of 100 kW (fuel power input) DFB gasifier pilot plantscurrently in operation
→ Large scale (8 MW fuelpower) plant for CHP generation in successfuloperation since 2001
→ 2nd unit in operation since2009 (10 MW)
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 15T. Pröll
Gasifier improvement efforts
char
com
bust
or
gasifier
ULS
LLS
air
fuel
exhaust gas
product gas
steam
char
com
bust
or
gasi
fier
ULS
LLS
air
fuel
steam
G-ILS
exhaust gas
product gas
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 16T. Pröll
New dual CFB design
Fuel reactor divided in verticalsections by areas of reducedcross section
Fast fluidization regime in thereduced cross section, bubbling to turbulent regime in the zones between
Consecutive dense zones
Gas-solid counter-currentflow behavior
Particle size separation
airr
eact
or(A
R)
exhaust AR
fuelreactor(FR)
exhaustFR
air steam
ULS
LLS
LS
solid fuel
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 17T. Pröll
Cold flow model testing
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 18T. Pröll
Local behavior
pressure, qualitative Solids density (1 – )
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Institute of Chemical EngineeringResearch Group Future Energy Technology
www.chemical‐looping.at 19T. Pröll
Conclusion/Outlook
Small geometrical change may be key to make dual bed systemssignificantly more efficient in fuel conversion
Erosion seems manageable, expected velocities 1 - 5 m/s
Significant acceleration effects around flow obstacles
Ongoing: investigation at three different cold flow models withvarious particles Determination of suitable operating regimes
Next step: 150-200 kW pilot unit (gasification and possibly CLC)
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Contact:Tobias Pröll
tobias.proell@tuwien.ac.atwww.chemical‐looping.at
Institute of Chemical EngineeringResearch Group Future Energy Technology
Prof. Hermann Hofbauer
Getreidemarkt 9/166 1060 Wien
www.vt.tuwien.ac.at
Acknowledgement:
Financial support from the Austrian Government Climate and Energy Programmefor the research project NE-IF 821954 "G-volution" is greatfully acknowledged.
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