Upload
lethu
View
226
Download
0
Embed Size (px)
Citation preview
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
2
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
3
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?
4
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
5
Typical Advantages ofOxygen� Increased efficiency (lower sensible heat
loss)� less fuel required
� Throughput increase
� Lower capital requirements
� Potential for pollution reduction
6
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
7
Known Benefits of O2 inBoilers� Conventional benefits
� increased efficiency
� Boiler operation benefits� capacity recovery after fuel switching� overcome fan limitations
8
Barriers to O2 Use inBoilers� Cost
� Site safety concerns
� Siting requirements for on-site oxygenplants or large storage tanks
9
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
10
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
11
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
12
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
13
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
14
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
15
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
16
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
17
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%
18
L1500 - Furnace
19
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
20
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
21
Industrial Scale BurnerFacility
ISBF
SOFA 1 SOFA 2
HeatExchanger
33'-2"
TC
TC
TCTC
Water Jacket
FlameBurner
22
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
23
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
24
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
25
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
26
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)
27
"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".