EXPERIMENTAL AND KINETIC

Transcription

1 EXPERIMENTAL AND KINETIC MODELING STUDY OF THE EFFECT OF SO 2 ON FUEL OXIDATION IN AN O 2 /CO 2 ATMOSPHERE J. Giménez*, M. Martinez, A. Millera, R. Bilbao, M.U. Alzueta I3A - University of Zaragoza - Spain 1 st Oxyfuel Combustion Conference Cottbus, 10/09/09

2 CONTENTS INTRODUCTION EXPERIMENTAL SETUP EXPERIMENTAL RESULTS KINETIC MODELING CONCLUSIONS

3 INTRODUCTION SO 2 Emissions: Oxyfuel Combustion compared to air In general, oxyfuel combustion can decrease SO 2 emissions compared to air combustion: Higher SO 2 volumetric concentration Flue gas recirculation Lower mass emission rate Sulphur retention by ash Deposits in the furnace A fraction of SO 2 may be further oxidized to SO 3

4 INTRODUCTION SO 2 Effect on oxidation processes In air combustion, SO 2 generally inhibits fuel oxidation Dagaut et al., Int. J. Chem. Phys. 35, 2003, 564 SO 2 effect on the oxidation of CO-H 2 mixtures under jet-stirred and flow reactor conditions: Fuel-lean lean conditions small inhibition Stoichiometric and fuel-rich conditions strong inhibition Alzueta et al., Comb. Flame 127, 2001, 2234 SO 2 effect on the oxidation of CO under flow reactor conditions: CO promotion close to stoichiometric conditions, in the range 0.7 < λ < 5 for low SO 2 concentrations.

5 INTRODUCTION SO 2 Effect on oxidation processes There is still controversy of the effect of the presence of SO 2 on the oxidation processes in air combustion SO 2 effect not studied under oxyfuel combustion conditions OBJECTIVES Study of the effect of the presence of SO 2 on CO oxidation under oxyfuel combustion conditions: Focus on the SO 2 chemistry EXPERIMENTAL: Laboratory scale flow reactor SIMULATION: Development of a chemical kinetic model

6 EXPERIMENTAL SETUP 1. Gas cylinders 2. Flux control 3. Water addition FEED SYSTEM UPSTREAM REACTION SYSTEM 4. Oven 5. Flow Reactor 6. Oven Control 11. Bubble flow meter 7. Compressor 8. Condenser 9. FTIR 10. MicroGC DOWNSTREAM

7 EXPERIMENTAL SETUP 1. Gas cylinders FEED SYSTEM 2. Flux control TEMPERATURE PROFILES 3. Water 1500 addition 11. Bubble 1200 flow meter UPSTREAM REACTION SYSTEM 4. Oven 5. Flow Reactor 6. Oven Control T (ºC) Lenth (cm) 7. Compressor 8. Condenser 9. FTIR 10. MicroGC DOWNSTREAM

8 EXPERIMENTAL SETUP Experimental conditions: 2000 ppm CO Variation in O 2 concentration Excess air ratio: O real λ = 2 O stoich 2 Absence/presence of SO 2 (1000 ppm) Dilution: CO 2 or N 2 T = K P = 1 atm Q = 1000 Nml/min t R = 8230/T(K) s

9 EXPERIMENTAL RESULTS Influence of the presence of SO 2. Comparison N 2 vs CO 2 dilution 1,00 0,75 0,50 - CO 2 dilution - CO 2 dilution T(K) λ = N 2 dilution - N 2 dilution Comparison N 2 vs CO 2 : Inhibition of CO oxidation in the CO 2 atmosphere, due to competition between: CO 2 + H CO + OH 2 O 2 + H O + OH

10 EXPERIMENTAL RESULTS Influence of the presence of SO 2. Comparison N 2 vs CO 2 dilution 1,00 0,75 - CO 2 dilution - CO 2 dilution 2 2 λ = N 2 dilution - N 2 dilution Influence of SO 2 : 0, T(K) The presence of SO 2 inhibits CO oxidation in both atmospheres The SO 2 effect seems to be higher in air combustion

11 EXPERIMENTAL RESULTS λ = 0.7 1,00 1,00 0% CO 2 25% CO , ,75 0,50 0,50 1,00 %CO 2 Lower SO 2 inhibiting effect 1,00 0,75 55% CO 2 0,75 75% CO 2 0,50 0, T (K) T (K)

12 EXPERIMENTAL RESULTS Influence of the presence of SO 2 The SO 2 inhibiting effect on CO oxidation under oxyfuel conditions has been observed to be caused by similar radical recombination mechanisms than for the air combustion case: SO 2 + O (+M) SO 3 (+M) SO 3 + HO 2 HOSO 2 + O 2 HOSO 2 (+M) SO 2 + OH (+M) O + HO 2 OH + O 2 H +SO 2 + M HOSO + M 2 HOSO + O 2 HO 2 + SO 2 H + O 2 HO 2 The lower availavility of H radicals under oxyfuel conditions slightly reduces the SO 2 inhibiting effect

13 EXPERIMENTAL RESULTS: Stoichiometry 1,00 1,00 0,75 without t SO 2 0,75 0,50 0,50 [O 2 ] Lower SO 2 inhibiting effect 1,00 0,75 1,00 0,75 0,50 0, T (K) T (K)

14 EXPERIMENTAL RESULTS Influence of the stoichiometry under oxyfuel conditions FUEL-LEAN CONDITIONS: SO 2 radical recombination via HOSO and SO 3 formation. 3 SO 3 pathway becomes more important as [O 2 ] increases HOSO 2 +HO 2 +M SO 3 +O(+M) +H(+M) SO +O 2 2 +O 2 HOSO HOSO 2 SO FUEL-RICH CONDITIONS: HOSO formation is the main pathway of SO 2 radical recombination +M +HO 2 +H +O 2 +O(+M) +H(+M) SO 3 SO +O 2 +O 2 +H(+M) +M HOSO HSO 2

15 EXPERIMENTAL RESULTS Influence of the presence of NO λ = 1 1,00 and NO, without NO with NO, 0,75 and NO [SO 2 ] = 1000 ppm [NO] = 1000 ppm 050 0,50 Both SO 2 and NO inhibit CO oxidation T(K) The effect of SO 2 and NO on CO oxidation is similar

16 EXPERIMENTAL RESULTS Influence of the presence of NO NO promoting effect: Promote conversion of less active NO +HO 2 = NO 2 + OH radicals (HO 2 ) to active radicals (OH) NO inhibiting effect: NO can catalyze recombination of radicals (similar to SO 2 ) NO + O + M NO 2 + M NO 2 + H NO + OH NO + H + M HNO + M O + H OH HNO + H NO + H 2 H + H H 2 HNO + OH NO + H 2 O H + OH H 2 O

17 KINETIC MODELING Development of a chemical kinetic model able to reproduce the experimental results. Software: Plug Flow Reactor Model of CHEMKIN-PRO Reaction Mechanism: Two elementary reaction subsets: Hydrocarbons oxidation and NO/NO x chemistry from Alzueta et al. (2008), based on previous work by Skjøth-Rasmussen et al. (2003). Sulphur chemistry from Alzueta el al. (2001), based on previous work by Glarborg et al. (1996). Modifications: Rate constant of reaction H+SO 2 +M=HOSO+M: Blitz et al. (2006) HOSO termochemistry: Wheeler and Schaefer (2009)

18 2000 KINETIC MODELING Experimental Initial Mechanism Modified mechanism 2000 CO (ppm) CO (ppm) Very good agreement between experimental data and the updated model CO (ppm) 1000 CO (ppm) T (K) T (K)

19 CONCLUSIONS Study of the effect of the presence of SO 2 on CO oxidation under oxyfuel combustion conditions: Comparison between air and oxyfuel combustion: Inhibition of CO oxidation under oxyfuel conditions SO 2 inhibit CO oxidation in both atmospheres Slightly lower inhibition in oxyfuel combustion Influence of the different parameters under oxyfuel conditions: Stoichiometry: t Lower SO 2 inhibiting effect as [O 2 ] increases Presence of NO: NO inhibit CO oxidation in a similar way as SO 2 and with similar effect.

20 CONCLUSIONS Simulation: A kinetic mechanism taken from literature for hydrocarbon oxidation, including SO x and NO x chemistry, has been updated in the present work The updated model obtains a good agreement with the experimental results

21 EXPERIMENTAL AND KINETIC MODELING STUDY OF THE EFFECT OF SO 2 ON FUEL OXIDATION IN AN O 2 /CO 2 ATMOSPHERE J. Giménez*, M. Martinez, A. Millera, R. Bilbao, M.U. Alzueta Aragón Institute of Engineering Research University of Zaragoza - Spain 1 st Oxyfuel Combustion Conference Cottbus, 10/09/09