Plasma-Enhanced SCR of NOx in Simulated Heavy-Duty Exhaust: Sulfur, Hydrocarbon, and Temperature Effects CL Aardahl, CF Habeger, KG Rappe, DN Tran, M Avila, and ML Balmer PW Park Caterpillar, Inc. DOE Program Manager: G Singh (OTT-)
Outline Background Information High-Temperature Plasma System Results from Catalyst Testing - Temperature Effects - Efficiencies - Hydrocarbon Quantity and Form - Sulfur Effects Future Plans
Plasma Catalysis Program (3/99 Start) Challenges Stability, Durability, and Activity over a Broad Temperature Range -Focus on Higher End of Temperature Range -Numerous other Programs Examining the Low End Large Exhaust Flow and Low HC Concentration Technical Approach Design a High-Temperature Plasma Reactor Develop Novel High-Temperature Catalysts PNNL Synthesis, Characterization, Plasma Testing Caterpillar Synthesis, Characterization, Engine Testing Develop Mechanistic Understanding Reactant Variation (NOx, SO 2, HC, H 2 O) Catalyst Surface Analysis Pre- and Post-Mortem
Ideal Reaction: Plasma Chemistry NO + N fi N 2 + O Reactions that Dominate: NO + O fi NO 2 NO 2 + O fi NO + O 2 NO 2 + OH fi HNO 3 HC Is an O and OH Getter: C 3 H 6 + O fi C 2 H 5 + HCO C 3 H 6 + O fi CH 2 CO + CH 3 + H C 3 H 6 + OH fi C 3 H 5 + H 2 O C 3 H 6 + OH fi C 3 H 6 OH Oxidation Products Form HO 2 : CH 3 O + O 2 fi CH 2 O + HO 2 HCO +O 2 fi CO + HO 2 H +O 2 fi HO 2 HO 2 Reacts Quickly w/no: NO + HO 2 fi NO 2 + OH Penetrante et al. (SAE SP-1395)
Process Flow Sheet G C -M S F T IR N O x M ET E R D IF F U S IO N D R Y ER O F F -G A S T R E A T M EN T G A S M A KE -U P (D R Y G A S) P LA S M A C A T AL Y ST FURNACE 1 FURNACE 2 T, H H U M ID IF IE R N 2 B A LA N C E
Gas Composition and Test Conditions Make-Up NO 5 ppm SO 2 /2 ppm O 2 9% CO 3 ppm C 3 H 6 5 2 ppm CO 2 8% H 2 O 1.5% N2 balance Catalyst: 1 gram Bulk Sp. Grav.:.25.4 Flowrate: 1 SLM Space Velocity: 15, 25, 1/hr
Power Deposition vs. Temperature 1.2 1 SLM on small-scale reactor Packed-bed and single-barrier reactors failed Power Deposited, W 1.8.6.4.2 2 o C 5 o C 2 3 4 5 6 7 8 9 1 Voltage Across Reactor, kv High-temperature stability gained by using dual-dielectric barrier system Power vs. voltage better as T because electron mean free path increases.
Thermodynamics Effects on NO fi NO 2 1 NO + ½ O 2 fi NO 2 8 NO 2 NOx, % 6 4 2 NO LLNL (SAE SP-1395) PNNL 2nd Order Fit 2 4 6 8 T, o C
HC Level Study (PF#1) 6 2 o C 8 NOx Converted, % 5 4 3 2 5 ppm 1 1 ppm 2 ppm 1 2 3 4 5 6 7 8 Energy Deposited, J/L NOx Converted, % 7 6 5 4 3 5 ppm 2 1 ppm 1 2 ppm 2 4 6 8 1 Energy Deposited, J/L No SO 2 used in this study.
HC Level Study 5 o C NOx Converted, % 8 7 6 5 4 3 2 PF#1 5 ppm 1 ppm 2 ppm 2 4 6 8 1 Energy Deposited, J/L As temperature increases, optimal C 1 :NOx ratio also increases 2 o C: 3:1 sufficient : 6:1 5 o C: 12:1 (greater?)
HC Consumption vs. Temperature Propene Level, ppm 2 15 1 5 1 2 3 4 5 6 7 8 Energy Deposited, J/L 2 o C - Plasma 5 o C 2 o C - Catalyst 5 o C
NO to NO 2 (Plasma) NO Converted, % 1 8 6 4 2 2 ppm 15 1 5 25 125 no propene NO Converted, % 1 8 6 4 2 1 ppm Propene - SO 2 Propane - SO 2 Propene - no SO 2 5 1 15 Energy Deposited, J/L Propane - no SO 2 5 1 15 Energy Deopsited, J/L
Energetics of Propene Oxidation 3 25 5 ppm 1 ppm 2 ppm C = C i exp E β β 2 15 1 5 2 3 4 5 Temperature, o C As HC level increases: More difficult to oxidize same fraction of HC at a given temperature (higher β). Enhanced oxidation due to increased temperature is more significant.
Sulfur Tolerance of PF#1 NOx Converted, % 8 7 6 5 4 3 2 1 2 ppm C 3 H 6 1 2 3 4 5 6 7 Energy Deposited, J/L 2 o C - no SO 2 5 o C 2 o C - w/ SO 2 5 o C
Sulfur Tolerance of PF#2 1 NOx Converted, % 8 6 4 2 2 ppm C 3 H 6 1 2 3 4 5 6 7 8 Energy Deposited, J/L 2 o C - no SO 2 5 o C 2 o C - w/ SO 2 5 o C
Transient Response to SO 2 PF#2 7 2 ppm SO 2 added at t = NOx Converted, % 65 6 55 NO NOx Energy deposition held at 61 J/L Poisoning takes place over 4-6 hours at 2 ppm HC. Poisoning is irreversible. 5 5 1 15 2 25 Loss in efficiency shows up as NO and NO 2. Time, min.
Saturated vs. Unsaturated HC NOx Converted, % PF#1 2 ppm HC 8 7 2 o C - Propene 6 5 4 5 o C 3 2 o C - Propane 2 1 5 o C 1 2 3 4 5 6 7 Energy Deposited, J/L
Conclusions 1. High-temperature plasma is possible and reliable. 2. Optimum HC level changes with temperature due to changes in NO conversion, HC oxidation, and catalyst activity. May be beneficial to inject postplasma. Optimal HC levels are too high. 3. Sulfur poisoning is a problem for certain catalysts. Other formulations show relatively minor degradation in activity. More aging and long-term studies needed.