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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

Combination & Integration of DPF-SCR Aftertreatmentenergy.gov/sites/prod/files/2014/03/f8/deer12_rappe.pdf · Combination & Integration of DPF-SCR Aftertreatment ... DOC cDPF SCR

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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

30

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

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~7.4 kPa @ ~0.36 g/L soot

Downstream 150 g/L SCR catalyst

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~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