combination & integration of dpf-scr aftertreatment oxidation and scr reaction components the...
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Combination & Integration of DPF-SCR Aftertreatment
PNNL:
Ken Rappe, Mark Stewart, Gary Maupin
PACCAR: Rich Bergstrand (PTC), Mansour Masoudi (PTC),
Wim Evers (DAF), Bram Hakstege (DAF)
BASF: Patrick Burk
DEER 2012
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
AFTER-TREATMENT COMPLEXITY Integrating DPF & SCR functionalities for reducing
cost and volume of engine after-treatment
Engine Exhaust
fuel urea DOC cDPF SCR
Engine Exhaust
fuel urea DOC DPF/SCR
Typical HDD EPA 2010 Layout
Possible Future HDD Layout
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
SCR – DPF INTEGRATION
OBJECTIVE: Fundamentally understand the integration of SCR & DPF technologies for HDD to provide a pathway to the next generation of emissions control systems
CRADA with PACCAR, working closely with DAF Trucks
Highly evolving field of work (mostly LDD, some HDD); this effort focused on: 1. Optimizing SCR catalyst wash coat 2. Facilitating passive soot oxidation
BASF (HD Systems Development) Providing SCR catalyst (Cu/Z) expertise Washcoating, manufacturability
Corning Developmental UHP cordierite
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
SCR – DPF INTEGRATION
OBJECTIVE: Fundamentally understand the integration of SCR & DPF technologies for HDD to provide a pathway to the next generation of emissions control systems
CRADA with PACCAR, working closely with DAF Trucks
Highly evolving field of work (mostly LDD, some HDD); this effort focused on: 1. Optimizing SCR catalyst wash coat 2. Facilitating passive soot oxidation
BASF (HD Systems Development) Providing SCR catalyst (Cu/Z) expertise Washcoating, manufacturability
Corning Developmental UHP cordierite
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
Flow
FlowCu/Z slurry
Cu/Z slurry
OPTIMIZING SCRF WASHCOAT
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
Flow
FlowCu/Z slurry
Cu/Z slurry
OPTIMIZING SCRF WASHCOAT
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
Flow
FlowCu/Z slurry
Cu/Z slurry
0
5
10
15
20
25
30
0 1 2 3 4 5
Pre
ssu
re D
rop
, k
Pa
Accumulated Soot, g/L
∆P after initial loading phase~11.5 kPa @ ~0.5 g/L soot
Upstream 90 g/L SCR catalyst
0
5
10
15
20
25
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0 1 2 3 4 5
Pre
ssu
re D
rop
, k
Pa
Accumulated Soot, g/L
∆P after initial loading phase~3.2 kPa @ ~0.38 g/L soot
Downstream 90 g/L SCR catalyst
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5
10
15
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0 1 2 3 4 5
Pre
ssu
re D
rop
, k
Pa
Accumulated Soot, g/L
∆P after initial loading phase~7.4 kPa @ ~0.36 g/L soot
Downstream 150 g/L SCR catalyst
0
5
10
15
20
25
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0 1 2 3 4 5
Pre
ssu
re D
rop
, k
Pa
Accumulated Soot, g/L
∆P after initial loading phase~20.5 kPa @ ~0.52 g/L soot
Upstream
150 g/L SCR Catalyst
OPTIMIZING SCRF WASHCOAT
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
REACTION STUDIES
Reaction competition Passive soot oxidation vs. Selective catalytic reduction (SCR)
Passive soot oxidation – NO2 driven The presence of SCR reaction(s) in a wall-flow filter WILL have a detrimental effect on passive soot oxidation SCRF integration will NOT have oxidation component on filter, thus no NO2 ‘recycle’ component present Reaction competition: passive soot oxidation vs. SCR
GOAL: maximize the passive soot oxidation feasibility of an SCRF
Minimize adverse effect of SCR on passive soot oxidation process No additional downstream SCR
cannot sacrifice acceptable de-NOx performance
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
REACTION STUDIES
MODELING WALL-SCALE SCRF
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
MODELING WALL-SCALE SCRF
Single flat wall; exhaust flow in the normal direction
Channel scale transport effects, axial variations are ignored
Simplified SCR reaction network developed at PNNL
Simplified porous media with similar porosity and tortuosity of the SCRF used in experiments
90 g/L of catalyst distributed evenly throughout the porous wall + 60 g/L placed on down-stream wall surface
Lattice-Boltzmann model used to solve gas flow field
Soot oxidation kinetic model by Messerer et al, 2006
Soot present as cake layer on top of wall; assumed 50% oxidized soot
Conclusions dependent upon validity of assumptions and kinetics used
Standard Conditions 4 g/L soot 150 g/L catalyst 500 ppm NOX 35,000 GHSV ANR = 1
exhaust flow
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
MODELING WALL-SCALE SCRF
Simplified SCR kinetics model Developed under CLEERS in cooperation with ORNL using bench-scale experiments with a current commercial cu-CHA catalyst
NH3 oxidation 2NH3 + 3/2O2 → N2 + 3H2O Standard SCR 4NH3 + 4NO + O2 → 4N2 + 6H2O Fast SCR 4NH3 + 2NO + 2NO2 → 4N2 + 6H2O
Parametric matrix 250°C, 300°C, 350°C, 400°C, 450°C NO2/NOx = 0.33, 0.50, 0.67; NH3/NOx = 1.0, 0.85 DPF versus SCRF
Diffusivity adjusted for temperature (Massman, 1998)
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
MODELING WALL-SCALE SCRF Example species fields – 350°C In all SCRF cases: SCR catalyst creates gradients in active species concentrations and NH3 surface coverage across the wall thickness
NH3 dosing ON NH3 dosing OFF NO2 [ppm] NO [ppm] NH3 surface coverage NO2 [ppm] NO [ppm] NH3 [ppm]
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
MODELING WALL-SCALE SCRF Example species fields – 350°C Gradients in active species concentrations facilitate diffusion effects that are significant and effect concentrations upstream Of particular interest: NO2
NO2 [ppm] NO [ppm] NH3 surface coverage NO2 [ppm] NO [ppm] NH3 [ppm]
39 ppm 70 ppm
NH3 dosing ON NH3 dosing OFF
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
MODELING WALL-SCALE SCRF Passive soot oxidation (ANR = 1)
Impact of SCR on soot oxidation is temperature dependent
SCR reactions decrease oxidation rate by about 35% at intermediate temperatures, but only 4% at higher temperatures
Increased NO2 fraction decreases inhibiting effect of SCR
00.10.20.30.40.50.60.70.80.9
1
250 300 350 400 450Temperautre (C)
Ratio SCRF/DPF ox rate
0.64
0.65
0.66
0.67
0.68
0.69
0.7
0.33 0.43 0.53 0.63NO2/NOX Ratio
Ratio SCRF/DPF ox rateRatio of soot oxidation rates [w/NH3 dosing / w/o NH3 dosing]
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
MODELING WALL-SCALE SCRF
Full simulation (as described in initial model description) Simplified porous media with similar porosity and tortuosity of the SCRF used in experiments 90 g/L of catalyst distributed evenly throughout the porous wall + 60 g/L placed on down-stream wall surface Soot present as cake layer on inlet channel surface of porous media
Lumped simulation Soot & SCR catalyst co-located No porous media Provides initial guesses for SS concentrations and NH3 coverage
Comparison provides a means of evaluating effect of spatial separation within wall-flow filter
Soot oxidation and SCR reaction components the same Bulk-flow (i.e. convective) component the same Allows evaluation of effect of concentration gradient(s) and resulting conductive transport (i.e. diffusive) effects
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
MODELING WALL-SCALE SCRF Spatial separation within wall-flow filter Spacial separation (of SCR from soot) results in a small benefit for soot oxidation and NRE
Benefit for soot oxidation smaller
Effect is small: kinetics of competing reactions and resulting conductive transport effects dominant for all cases
1.081.1
1.121.141.161.18
1.21.221.241.261.28
250 300 350 400 450Temperautre (C)
Full/lumped NOX removal eff
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
1.08
250 300 350 400 450Temperautre (C)
Full/lumped oxidation rate
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
REACTION STUDIES
BENCH-SCALE REACTION STUDIES
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NOX REDUCTION EFFICIENCY Effect of NO2 fraction on NRE
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
150 200 250 300 350 400 450 500
NO
xRe
duct
ion
Effic
ienc
y
Temperature, °C
500 ppm NOxANR = 1Selective Catalytic Reduction
150 g/L SCR catalyst loadingwithout soot
NO2/NOx = 0.65
NO2/NOx = 0.35NO2/NOx = 0.5
SCR performance: Minimally affected at NO2 /NOx < 0.5 Detrimental effect at NO2 /NOx > 0.5
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NOX REDUCTION EFFICIENCY Effect of NO2 fraction on NRE
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
150 200 250 300 350 400 450 500
NO
xRe
duct
ion
Effic
ienc
y
Temperature, °C
500 ppm NOxANR = 1Selective Catalytic Reduction
Flow Through SCR~170 g/L catalystNO2/NOx = 0.5
Detrimental effect of wall flow versus flow through Especially at temp < ~275°C
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NOX REDUCTION EFFICIENCY Effect of NO2 fraction on NRE
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
150 200 250 300 350 400 450 500
NO
xRe
duct
ion
Effic
ienc
y
Temperature, °C
500 ppm NOxANR = 1Selective Catalytic Reduction
150 g/L SCR catalyst loadingwith 4 g/L initial soot loading
NO2/NOx = 0.35
NO2/NOx = 0.65
NO2/NOx = 0.5SCR performance not significantly affected by soot NO2 /NOx > 0.5 improved Contribution of passive soot oxidation
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
PASSIVE SOOT OXIDATION Effect of NO2 fraction on soot oxidation rate
0
0.44
0.88
1.32
1.76
2.2
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
500 ppm NOxANR = 1
150 g/L SCR catalyst loadingPassive Soot Oxidation4 g/L initial soot loading
NO2/NOx = 0.35
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
PASSIVE SOOT OXIDATION Effect of NO2 fraction on soot oxidation rate
0
0.44
0.88
1.32
1.76
2.2
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
500 ppm NOxANR = 1
150 g/L SCR catalyst loadingPassive Soot Oxidation4 g/L initial soot loading
NO2/NOx = 0.35
NO2/NOx = 0.5
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
PASSIVE SOOT OXIDATION Constant NOx: effect of NO2 fraction on soot oxidation rate
0
0.44
0.88
1.32
1.76
2.2
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
500 ppm NOxANR = 1
150 g/L SCR catalyst loadingPassive Soot Oxidation4 g/L initial soot loading
NO2/NOx = 0.65
NO2/NOx = 0.35
NO2/NOx = 0.5
Increased NO2 facilitates increased soot oxidation Combined effect of more NO2 and increased NO2 fraction
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
PASSIVE SOOT OXIDATION Separating NO2 fraction
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
500 ppm NO2ANR = 1
Passive Soot Oxidation4 g/L initial soot loading
NO2/NOx = 0.33ANR = 0
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
PASSIVE SOOT OXIDATION Separating NO2 fraction
NO2 constant, varying total NOx
NO2/NOx 0.33 → 0.5 No improvement in passive oxidation
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
500 ppm NO2ANR = 1
Passive Soot Oxidation4 g/L initial soot loading
NO2/NOx = 0.33
NO2/NOx = 0.5
ANR = 0
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
PASSIVE SOOT OXIDATION Separating NO2 fraction
NO2 constant, varying total NOx
Fast SCR dominating KEY: Availability of NO2 past equimolar NO:NO2 reaction
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
500 ppm NO2ANR = 1
Passive Soot Oxidation4 g/L initial soot loading
NO2/NOx = 0.5
ANR = 0 NO2/NOx = 0.65
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NOx SLIP Separating NO2 fraction
NO2 constant, varying total NOx
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
150 200 250 300 350 400 450 500
Frac
tion
of N
Ox
slip
Temperature, °C
500 ppm NO2ANR = 1 NO2/NOx = 0.33
NO2 slip
NO slip
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NOx SLIP Separating NO2 fraction
NO2 constant, varying total NOx
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
150 200 250 300 350 400 450 500
Frac
tion
of N
Ox
slip
Temperature, °C
500 ppm NO2ANR = 1 NO2/NOx = 0.5
NO2 slip
NO slipNO2/NOx 0.33 → 0.5 Extremely similar NO & NO2 fraction of NOX slip
Thus similar oxidation behavior
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NOx SLIP Separating NO2 fraction
NO2 constant, varying total NOx
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
150 200 250 300 350 400 450 500
Frac
tion
of N
Ox
slip
Temperature, °C
500 ppm NO2ANR = 1 NO2/NOx = 0.65
NO2 slip
NO slip
NO2/NOx 0.5 → 0.65 Increased NO2 fraction of NOX slip
Demonstrates NO2 availability and subsequent key role in passive oxidation
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NH3/NOx RATIO
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
1000 ppm NOXNO2/NOx = 0.5
Passive Soot Oxidation4 g/L initial soot loading
ANR = 0
ANR = 1
Effect of decreased NH3/NOx ratio at NO2/NOx = 0.5
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NH3/NOx RATIO Effect of decreased NH3/NOx ratio at NO2/NOx = 0.5
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
1000 ppm NOXNO2/NOx = 0.5
Passive Soot Oxidation4 g/L initial soot loading
ANR = 0
ANR = 1
ANR = 0.7
At NO2/NOx = 0.5 Soot oxidation affected little by decreased ANR (supported by modeling and NO2 concentration profile)
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
NH3/NOx RATIO Effect of decreased NH3/NOx ratio at NO2/NOx = 0.65
0
0.2
0.4
0.6
0.8
1
1.2
150 200 250 300 350 400 450 500
Pres
sure
Dro
p, re
lativ
e
Temperature, °C
500ppm NOxNO2/NOx = 0.65
ANR = 0.85
Passive Soot Oxidation
ANR = 0
ANR = 1
At NO2/NOx > 0.5 Decreased ANR facilitates greater soot oxidation KEY: NO2 availability
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
SUMMARY DPF-SCR INTEGRATION
Facilitating passive soot oxidation Reaction competition: passive soot oxidation vs. SCR KEY: NO2 balance in the system, with the primary driver being the fast SCR reaction (equimolar NO & NO2 consumption)
Modeling can help guide us to develop an understanding of proper reactive and thermal management of SCRF
Implementation & control – Truck & engine OEMs Thermal management DOC specification etc.
DEER 2012
PNNL INSTITUTE FOR INTEGRATED CATALYSIS
ACKNOWLEDGEMENTS
Work funded through DOE’s Vehicle Technologies Program BASF – Heavy Duty Systems Development Group Corning Dr. Maruthi Devarakonda (formerly PNNL)
SCR kinetic model development