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SCR-DPF integrations for diesel exhaust Performance and perspectives for high SCR loadings DEER conference, 2012-10-17 Milica Folić/Keld Johansen
SCR-DPF integrations for diesel exhaust Performance and perspectives for high SCR loadings
DEER conference, 2012-10-17
Milica Folić/Keld Johansen
Outline SCR integration in DPF: Why and how?
Challenge: High temperature stable SCR
Filters types and porosities: Lab screening
Results on LD engine bench
Conclusions and future outlook
SCR integration with DPF: Why and how?
NOx PM HC CO NOx PM HC CO NH3 NOx PM HC CO
NO2
Urea Diesel
DOC ZSCR/DPF ASC/ DPF
NOx PM HC CO NH3
Urea
DOC ZSCR/DPF ZSCR VSCR ASC
Diesel
NOx PM HC CO NOx PM HC CO NH3 NOx PM HC CO
NO2
NOx PM HC CO NH3
Integration advantages: – Lower volume, cost
– Improved transfer: heat, gas components
– Earlier urea injection, improved cold start SCR
– Low exhaust temperature
High temperature stable SCR formulations SCR catalyst that tolerates up to 800-900°C?
– Fe-β-zeolite – not stable and requires NO2
– V2O5/ WO3/ TiO2 not stable
– Cu- β-zeolite – not stable
Cu chabazite (and alike) materials are good candidates – Cu-SAPO-34 chosen for this study (ZSCR)
– Cost-effective solution for small ring zeolites
Thermal effects and hydrothermal stability
Big difference in hydrothermal stability: Cu-Beta vs. Cu-SAPO-34
Cu-SAPO-34 must be activated @high T to obtain activity – Decrease in Cu surface concentration upon calcination
Comparison fresh and aged.300Nml/h, 40mg catalyst
10% O2, 5% H2O, 500ppm NH3, 450ppm NOx
0
10
20
30
40
50
60
70
80
90
100
100 150 200 250 300 350 400 450 500 550 600Temperature (°C)
NO
x co
nver
sion
(%)
Fe-ZSCRFe-ZSCR aged 16h/750CCu-ZSCR (type1)Cu-ZSCR (type1) aged 16h/750CCu-ZSCR (type2)Cu--ZSCR (type2) aged 16h/750C
Fe-Beta Fe-Beta aged 16h/750C Cu-Beta Cu-Beta aged 16h/750C Cu-SAPO-34 Cu-SAPO-34 aged 16h/750C
Filter materials: lab screening Candidates with porosity potential (57–75%) for SCR integration:
- SiC - Cordierite - ATI - Mullite
Coat load range 100–220 g/L depending on the filter material Focus on DeNOx performance and pressure drop
DeNOx/Δp optimal SCR loadings found
All samples benchmarked against flow-through monoliths
Notation:
– ’Low’ porosity: 57-60%
– ’Medium’ porosity: 65%
– ’High’ porosity: 75% !
Optimal coat load study: Low porosity at NHSV = 100,000 h-1
Above certain coat load only dP continues increasing
A small drop in NOx conversion observed at too high loads
Max Nox conversion vs dP for 250 and 400C.Different coat loads.
0
10
20
30
40
50
60
70
80
90
100
10 15 20 25 30 35 40dP [mbar]
max
NO
x co
nv [%
]
400°C250°C
SAPO-34 coating on different filters
NOx conversion proportional to coat load
High porosity gives best trade-off between dP and DeNOx
T=250°C. Porosity: Low vs Medium vs High
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40dP [mbar]
max
Nox
con
v [%
]
SCR ref, 125g/L, cord
SCR ref, 155g/L, cord
T=400°C. Porosity: Low vs Medium vs High
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40dP [mbar]
max
Nox
con
v [%
]SCR ref, 155g/L, cord
SCR ref, 125g/L, cord
DeNOx activity with NO2=f(Δp, T). Low porosity
For low porosity filters, addition of NO2 can help close the gap in activity between SCR/DPF and flow-through
Observed activity @ T=250°C.
0
50000
100000
150000
200000
250000
300000
0 5 10 15 20 25 30dP [mbar]
Flow-through cord. SCRF
NO2/NOx=0,1
NO2/NOx=0,1
NO2/NOx=0,3NO2/NOx=0,3
Kob
s [1
/h]
Kob
s [1
/h]
Observed activity @ T=400°C.
0
50000
100000
150000
200000
250000
300000
0 5 10 15 20 25 30dP [mbar]
NO2/NOx=0,3
NO2/NOx=0,3
NO2/NOx=0,1
Flow-through cord. SCRF
NO2/NOx=0,1
Kob
s [1
/h]
VSCR-DPF comparison with ZSCR-DPF
VSCR-DPF shows good high temperature activity [400-500°C]
BUT: Almost no low temperature activity left
0
10
20
30
40
50
60
70
80
90
100
200 250 300 350 400 450 500 550Temp [°C]
max
NO
x co
nv. [
%]
Flow through, ZSCR, 400 cpsi cordVSCR-DPF, Medium porosityZSCR-DPF, Medium porosityZSCR-DPF, High porosity
Max NOx conversion after 64hrs @750°C
Stability is proportional to the coat load/porosity
Little change in performance of high porosity filter
Max NOx conv. vs dP. Fresh and aged 64hrs @750C.T=250°C, NHSV=100000h-1, NOx,in=250ppm.
Low vs Medium vs High porosity
0
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25 30dP [mbar]
max
NO
x co
nv [%
]Max NOx conv vs dP. Fresh and aged 64hrs @750C.
T=400°C, NHSV=100000h-1, NOx,in=250ppm.Low vs Medium vs High porosity
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30dP [mbar]
max
NO
x co
nv [%
]
Ammonia storage upon ageing
Very stable ammonia storage capacity at 250°C
Higher storage for filters due to better contact with coat
0
50
100
150
200
250
300
350
400Fresh Aged 16h @750C Fresh Aged 64h @750C
Flow-through SCR SCR/DPF
µmol
/(g C
u-S
AP
O)
Laboratory findings Coat load optimum (120–180g/L) & coating procedure
established for various materials/porosities
High coat load gives the same DeNOx as flow-thorough
Satisfactory performance after ageing for 64hrs @750°C
Several porosity filters chosen for up scaling and engine bench tests with soot
1. Soot – Δp curve 2. Active soot regeneration (Tin=600 ºC, 4- 5 g/l) 3. Steady state NOx activity with soot (4-5 g/l) 4. WHTC: fresh & aged filter 5. NH3 absorption w & w/o soot 6. Passive/NO2 soot regeneration (BPT w & w/o urea) 8. PN and PM filtration 9. Drop to idle test (4-5 g/l) 10. Ash influence CAN TESTS WITH SOOT CHANGE THE OBTAINED LAB RATING?
Engine validation tests
DOC
Urea dosing
Hydolysis mixer
SCR/DPF
Engine bench: LD test cell Engine Volvo D5204T3
Displacement 1984 cm3
Rated power 120 (109) kW
Original emission level Euro 5
Original after treatment EGR + DOC + DPF
Engine out NOx WHTC 5.3 g/kWh
WHTC. ANR=0,8 for Low porosity filter
Overall conv
71. 3 %
Overall conv
71. 3 %
Overall conv
71. 3 %
NO2/NOx 70% DOC out
Average NHSV=38000h-1
Average Tbefore filter = 220°C
ANR NOx conv
[%]
Average NH3 slip [ppm]
0.8 71.3 37.4
1 81.4 100
Comparison with flow-through SCR
Filter Flow-through
NHSVav [h-1] 38000 47000
0
10
20
30
40
50
60
70
80
90
100
0 0,2 0,4 0,6 0,8 1 1,2 1,4ANR
-20
0
20
40
60
80
100
120
140
160Low Porosity SCR/DPFMedium Porosity SCR/DPFFlow-through SCR
NH
3 slip
[ppm
]
NO
x co
nv [%
]
Steady state DeNOx, low and medium porosity filters
NHSV=55000h-1. ANR=0,9. Conversion over DOC + ZSCR/DPF
0
20
40
60
80
100
200 250 300 350 400 450 500Temperature [°C]
Nox
con
vers
ion
[%]
0
100
200
NH
3 slip
[ppm
]
Conv Low PorosityConv Medium PorositySlip Low PorositySlip Medium Porosity
Passive regeneration @ T~350°C Low porosity filter Soot [g/l] No
urea With urea
Start 6.15 5.4
End 1.8 2.45
Regen. efficiency
71% 55%
BPT=295°C
0
5
10
15
20
25
30
35
40
0 500 1000 1500 2000 2500 3000 3500 4000
Time [s]
dP [k
Pa]
0
100
200
300
400
500
600
NO2
[ppm
], T
[°C]
dP [kPa]
dP w ith urea [kPa]
NO2 filter outlet [ppm]
T filter inlet [°C]
NO2 w ith urea [ppm]
T filter inlet w urea [°C]
Conclusions and future outlook SCR+DPF replacement with ’ZSCR/DPF only’ is possible
Good NOx conversions in test cycles for different porosities
High coat load gives equivalent activity to flow-through
dP for ZSCR/DPF is near traditional cDPF + SCR systems
Passive regeneration: SCR and soot compete for NO2. DOC must be optimized for high NO2
Active regeneration: max soot load and T ramping management need good control (thermal peaks risk)
Selection of high loading ZSCR/DPF requires full validation!
SCR-DPF integrations for diesel exhaust Performance and perspectives for high SCR loadings
DEER conference, 2012-10-17
Milica Folić/Keld Johansen
Henrik Bentzer Bjarne Møller Anni Stahl Jakob Høj Tais Jeppesen Shannie Nielsen Kenneth Larsen
