Simulation of Selective Catalytic Reduction using DARS 1D Tool

Transcription

1 Simulation of Selective Catalytic Reduction using DARS 1D Tool Best Practice Training: Combustion & Chemical Reaction Modeling STAR Global Conference 2013 Karin Fröjd & Adina Tunér LOGE AB

2 Outline Introduction Model SCR Reactor Model in DARS Chemical Scheme Results Validation Performance mapping Conclusions

3 Introduction DARS Reactors Homogeneous Theoretical Engine Reactors SRM (Stochastic Reactor Models) PaSR SRM-HCCI SRM-SI SRM-DICI SRM PPC DARS 1D Models SRM Pipe Coolers Aftertreatment Catalytic Converter Diesel Particulate Filter (DPF) Flames Premixed Burner stabilized Freely propagating Counter Flow Diffusion Back to Back Flamelet Single Library Chemical Mechanisms Development Analysis Reduction

4 Model: Catalyst Reactor Transient 1D Catalyst Model* Washcoat Reactor Three Level Solution: Reactor: Conductive Heat Transfer Channel: Flow and Gas Phase Chemistry, Heat and Mass Transport Washcoat: Surface Chemistry Channel * Fröjd, K. and Mauss, F., "A Three-Parameter Transient 1D Catalyst Model," SAE Int. J. Engines 4(1): , 2011, doi: /

5 Model: Catalyst Reactor Channels are discretized into a number of cells C i,p, Γ m, Ѳ m,j,t w washcoat p, v, Y i, h g k-1 k k+1 k+2 n-2 Monolith wall n-1 n n+1 Gas phase and surface chemistry is solved in each cell Heat conduction along the length of the catalyst is accounted for

6 Model: Catalyst Chemistry Handling Series of perfectly stirred reactors Chemistry is calculated in two subsections: Bulk gas Thin Film Layer (pores and wall surface) Heat and mass transfer between bulk gas and thin film layer are modeled using heat and mass transfer coefficients, calculated from Nusselt and Sherwood numbers. Detailed or global surface chemistry can be used. Gas phase chemistry in bulk gas can be modeled. Effectiveness factor can be used for surface chemistry.

7 Model: SCR Cu-ZSM Chemistry Olsson, L., Sjövall, H., Blint, R., A kinetic model for ammonia selective catalytic reduction over Cu-ZSM-5, Applied Catalysis B: Environmental 81 (2008) Ammonia adsorption and desorption NH 3 + S1 NH 3 S1 2. NH3 oxidation 2NH 3 S O 2 N 2 + 3H 2 O + 2S1 3. NO oxidation NO + 0.5O 2 NO 2 4. standard SCR 4NH 3 S1 + 4NO + O 2 4N 2 + 6H 2 O + 4S1 5. fast SCR 6. NO2 SCR 2NH 3 S1 + NO + NO 2 2N 2 + 3H 2 O + 2S1 4NH 3 S1 + 3NO 2 3.5N 2 + 6H 2 O + 4S1 7. N2O formation 2NH 3 S1 + 2NO 2 N 2 + N 2 O + 3H 2 O + 2S1

8 Model: SCR Cu-ZSM chemistry Chemical scheme captures NH3 adsorption and desorption, while still being simple. Good prediction of NH3 desorption peaks at increase of exhaust gas temperature. Easy to tune to a certain catalyst. CPU time efficient. All Cu-sites, Brönsted acid -sites and sites for weakly bound molecules are lumped into one site. Does not take into account storage of H2O, O2, NO2. NH 3 + S1 NH 3 S1 2NH 3 S O 2 N 2 + 3H 2 O + 2S1 NO + 0.5O 2 NO 2 4NH 3 S1 + 4NO + O 2 4N 2 + 6H 2 O + 4S1 2NH 3 S1 + NO + NO 2 2N 2 + 3H 2 O + 2S1 4NH 3 S1 + 3NO 2 3.5N 2 + 6H 2 O + 4S1 2NH 3 S1 + 2NO 2 N 2 + N 2 O + 3H 2 O + 2S1 CPU time: ~ real time on an ordinary laptop for one channel, on one CPU

9 Results: SCR catalyst Test conditions* Cu-zeolite (CU-ZSM-5) washcoat Tested different ramp regimes (Tin, NH3), and NH3 cut-off Catalyst inlet temperature in the range C (ct. or ramp) Catalyst length = 30 mm Channel hydraulic diameter = 1 mm Cell length = 3 mm (10 cells) *Olsson, L., Sjövall, H., Blint, R.J., A kinetic model for ammonia selective catalytic reduction over Cu-ZSM-5, Appl. Catalysis B: Environmental, Vol. 81, 2008,

10 Molefraction [:] Results Test 1: NH3 adsorption and desorption Constant ammonia inlet, followed by sudden cut-off. Temperature 150 ⁰C Upper panel: experiment and simulation by Chalmers University. 6.E-04 Lower panel: DARS simulation 5.E-04 4.E-04 3.E-04 NH3 inlet NH3 outlet 2.E-04 1.E-04 0.E Time [sec] 10

11 Molefraction NH3 in bulk gas[:] Site fraction NH3 at surface [:] Molefraction [:] Results Test 1: NH3 adsorption and desorption Ammonia slowly filling up surface sites until steady state is reached 6.0E E E E E E-04 NH3_GasOut NH3_GasIn 0.0E Time [min] 6.E-04 5.E-04 4.E-04 3.E-04 t=15 min 2.E-04 t=16.5 min 1.E-04 t = 18 min 0.E Distance along channel [m] 4.36E E E E E E E-01 t=15 min 4.22E-01 t=16.5 min 4.20E-01 t = 18 min 4.18E Distance along channel [m] Mole fraction ammonia in channel gas at different times Site fraction of adsorbed ammonia at different times 11

12 Temperature [K] / Concentration (ppm) Results Test 2: Temperature ramp. Inlet gas composition: 500 ppm NO, 500 ppm NH3, 8% O2, 5% H2O Upper panel: experiment and simulation by Chalmers University Lower panel: DARS simulation 1,200 1, InletT[K] NO_GasOut NO2_GasOut N2O_GasOut NH3_GasOut Time [min] 12

13 Molefraction H2O Molefraction O2 Results Test 2: Analysis Ammonia SCR for a temperature ramp. Inlet gas composition: 500 ppm NO, 500 ppm NH3, 8% O2, 5% H2O Direct oxidation of ammonia consumes part of the ammonia available at high temperatures 8.01E E-02 O2_GasOut 7.99E E E E E Time [min] 5.14E E E E E E-02 H2O_GasOut 5.02E E E Title 13

14 Molefraction Results Test 3: Inlet ammonia ramp. Inlet gas composition: 500 ppm NO, 8% O2. Temperature: 175⁰C Upper panel: experiment and simulation by Chalmers University Lower panel: DARS simulation Temperature [K] [K] InletT[K] NO_GasOut NO2_GasOut N2O_GasOut NH3_GasOut 7.00E E E E E E E Time [min] 0.00E+00 14

15 Temperature [K] Molefraction Results Test 4: Inlet ammonia ramp. Inlet gas composition: 250 ppm NO, 250 ppm NO2, 8% O2, 5% H2O. Temperature: 175⁰C Upper panel: experiment and simulation by Chalmers University E-04 Lower panel: DARS simulation InletT[K] NO_GasOut N2O_GasOut NH3_GasOut NO2_GasOut 5.00E E E E E E Time [min] 15

16 Results mapping Test 5-7: Mapping of NOx conversion and ammonia slip for different conditions. Base case: 450 ppm NO, 50 ppm NO2 (NO2/NOx = 0.1). 8% O ppm NH3 Temperature: 175⁰C Maps: Temperature - NH3/NOx ratio Temperature NO2/NOx ratio Catalyst length Site density 16

17 Results mapping Test 5: Temperature - NH3/NOx ratio map NOx Ammonia slip 4.50E E E E E E E E E E NH N2O T [deg C] 7.00E E E E E E E E NH T [deg C] 17

18 Results mapping Test 6: Temperature NO2/NOx ratio map NOx Ammonia slip 5.00E E E E E E E E E E E NO T [deg C] 5.00E E E E E E E E E E E NO T [deg C] 18

19 Results mapping Test 7: Catalyst length Site density map NOx NH3 3.50E E E E E E E E E E E E E Site density [mole/m2] Length [cm] 1.00E E E Site density [mole/m2] Length [cm] 19

20 DARS and STAR-CCM+ for SCR Modeling Urea spray in STAR-CCM+ Thermolysis and hydrolysis by DARS-CFD in STAR- CCM+ 1D SCR calculations in DARS Thermolysis and hydrolysis inside the channels can be calculated. Chemistry analysis in DARS SCR calculations in STAR-CCM+ by porous media. Consistent chemistry in all models 20

21 DARS and STAR-CCM+ for SCR Modeling Experimental data Raw chemistry Tuning of chemistry in DARS 1D Catalyst Tuned chemistry Application in STAR- CCM+ Performance mapping in DARS 1D Catalyst RESULTS 21

22 Conclusions DARS 1D with the SCR scheme from Chalmers provides a reliable and easy to use tool for SCR processes simulation. DARS 1D can be used to study transient performance of SCR catalysts. DARS SCR catalyst adds to the capabilities of DARS 1D family of models for covering full powertrain simulations. DARS SCR catalyst can be used for efficient parameter studies. DARS SCR catalyst and STAR-CCM+ can be combined for efficient process design

23 Thank you for your attention! Thank you for your attention!