oxygen enhanced combustion for nox control · high temperature oxy-fuel flames welding, flame...
TRANSCRIPT
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www.praxair.com
Copyright © 2001, Praxair Technology, Inc. All rights reserved.
O2 EnhancedCombustion forNOx Control
2002 Conference on SCRand SNCR for NOx Control
Pittsburgh PA,
May 15-16, 2002
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Acknowledgements
The authors wish to thank DoE NETL forproviding funding for this program.
Participants in this program include:
L. Bool, H. Kobayashi, KT Wu, D. Thompson - Praxair
E. Eddings, R. Okerlund - University of Utah
J.O.L Wendt - University of Arizona
M. Cremer, D. Wang - Reaction Engineering International
N. Nsakala, C. Maney, G. Richards, R. MacWhinnie - Alstom Power
S. Plasynski, DoE NETL
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Discussion Points
� Where has oxygen been used before?
� What role can oxygen play in utilityboilers?
� What is the effect of oxygen enhancedcombustion on NOx?
� What is the cost impact of using oxygen?
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Conventional O2 Use
� High temperature oxy-fuel flames� welding, flame polishing, cutting, etc.
� Oxygen addition for production rateincrease
� by O2 lancing� by O2 enrichment� by auxiliary oxy-fuel burners
� Full furnace conversion to oxy-fuel firing� fuel savings, NOx reduction, capital reduction� CO2 capture and sequestration
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Typical Advantages ofOxygen� Increased efficiency (lower sensible heat
loss)� less fuel required
� Throughput increase
� Lower capital requirements
� Potential for pollution reduction
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Where is O2 Used Now?
Industry Furnace/Kiln Applications
Steel Reheat, Soaking Pits, Ladles, Forging, EAFGlass MeltingCopper Smelting, AnodeAluminum Remelting, Coke CalciningPulp&Paper Lime kiln, Black LiquorCement Cement kilnPetroleum Fluid Cat. Cracker Regen., Claus SulfurChemical Incinerator, Sulfuric AcidClay Brick Kiln
Primarily High Outlet Temperature Processes
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Known Benefits of O2 inBoilers� Conventional benefits
� increased efficiency
� Boiler operation benefits� capacity recovery after fuel switching� overcome fan limitations
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Barriers to O2 Use inBoilers� Cost
� Site safety concerns
� Siting requirements for on-site oxygenplants or large storage tanks
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Oxygen for NOxReduction� Oxygen use can reduce NOx formation in
the primary combustion zone� promote flame attachment� enhance effectiveness of staged combustion
� Oxygen can enhance NOx destructiontechnologies in secondary combustionzone
� enhance coal-based reburning� enhance natural gas reburning and SNCR
� Oxygen reduces LOI/Unburned Carbon
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Oxygen with StagedCombustion
� O2 anchors coal flame
� O2makes gas phase morefuel rich
� O2 increases temperaturewhich enhances pyrolysisand accelerates NOxreduction kinetics
� O2 allows more fuel richoperation
O2enriched
firststage
OFA
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Approach
� Use an expert team to address criticalissues
� Praxair (oxy fuel combustion)� U of A (NOx formation)� U of U (combustion , burner development)� REI (CFD modeling)� ALSTOM (burner development)� Utility advisory panel (commercial application)
� Move from small-scale studies to pilot-scale testing, and finally large-scale burnertesting
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Program Timeline
Lab-
scal
e
CFD
Pilo
t-sca
le
Burn
er T
est
Dem
onst
ratio
n
Lab-
scal
eC
FD
1/00 1/01 1/02 1/03
Pilo
t-sca
le
CFD
Pilo
t-sca
le
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UA Experiments
� 17kW “premixed” pulverizedcoal downflow combustor
� Staged combustion
� Parametric study� response surface
methodology� O2 enrichment in first stage� SR in first stage� first stage residence time� O2 enrichment at staging
point
� Measurements� water cooled, water quenched
probe for gases� gas species NO, CO, CO2, O2
� ash for carbon burnoutAsh Trap
Exhaust
MistEliminator
Water CaptureSystem
PrimaryCondenser
NaturalGas Combustion Air
LowerSamples
0.0 / 1540
Timesec
//
TempK
UpperSamples
CoalTransportAir
0.5 / 1450
2.2 / 1140
Baghouse
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UA Experiments
0.00
0.10
0.20
0.30
0.40
0.50
0.60
First stage Stoichiometric ratio
NOx
(lb/M
MBt
u)
Oxygen addedAir alone
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Kinetic Model
� Proprietary model used to evaluateconcept
� Model of UA furnace agreed well withdata
� Model indicates O2 addition reducesNOx
� Parametric mixing studies suggestedNOx emissions below 0.10 lb/MMBtu
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REI Model
� Existing boiler model used to evaluateeffectiveness of oxygen
� NOx control� LOI
� Method of oxygen addition based onexperimental data
� Different burner type, including differentcoal spreader, that explored experimentally
� evaluate sensitivity to burner type
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CFD Modeling Resultsfor O2
2000
500K
Gas temperature (Side view, Centerline of the burners on the RHS)
Burner B
Burner C
Burner A
Burner D
OFA
AirNOx reduction: ---%LOI Reduction: ---%
A% replacementNOx reduction: 17%LOI Reduction: 12%
2A% replacementNOx reduction: 24%LOI Reduction: 24%
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L1500 - Furnace
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Results From L1500Testing
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Burner SR
NO
x at
out
let (
lb/M
MB
tu)
AirA% replacement2A% replacement3A% replacement
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ISBF Test Overview
� Well characterized boiler simulator at Alstom Powerhas been used to demonstrate oxygen enhancedcombustion using a full scale commercial burner.
� Various proprietary oxygen injection techniques wereevaluated
� Various parameters were measured: NOx, FOT,
CO, UBC
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Industrial Scale BurnerFacility
ISBF
SOFA 1 SOFA 2
HeatExchanger
33'-2"
TC
TC
TCTC
Water Jacket
FlameBurner
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Results From ISBFTesting
0.10
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% 14.0% 16.0%O2 replacement (%)
NO
x (lb
/MM
Btu
)
Phase I condition APhase I condition BPhase II
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Summary of Results
0%
5%
10%
15%
20%
25%
30%
35%
A% 2A% 3A%
Percent replacement of stoichiometric air
Redu
ctio
n fr
om a
ir c
ase
REIU. ArizonaU. UtahAlstom
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O2 Supply for UtilityOperation� Oxygen supply from
either onsite plant orproduct pipeline
� Oxygen plant can beeconomically scaledto accommodateunits from < 100 MWto 1,000 MW
� Well proven, reliabletechnology
Two bed Praxair VPSA plant
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But can we afford it?
� Minor burnermodificationrequired
� Other benefits� reduced LOI� increased
efficiency� reduced fan limits� technology
additive
Typical Economics*
*based on 5 month operation
0
500
1000
1500
2000
2500
3000
3500
4000
NOxCredits
SCR SNCR O2
$/to
n NO
x re
mov
ed
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Conclusions
� Testing and modeling indicate oxygenaddition can significantly reduce NOxemissions
� Even when initial NOx concentrations arelow O2 addition reduces NOx even further
� Oxygen is an economically attractivealternative to purchasing NOx credits orconventional technologies (SCR and SNCR)
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"This presentation was prepared with the support of the U.S. Department of Energy, under Award No. DE-FC26-00NT40756. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of the DOE".