Kinetic Study of CO-CO 2 Reaction with MO x -CaO-SiO 2 Slags

Transcription

1 Kinetic Study of CO-CO 2 Reaction with MO x -CaO-SiO 2 Slags Gary Gao Supervisor: Dr. Ken Coley /11/2006 1

2 Outline Background Technical need Gas-slag reaction mechanism Kinetic Model Objectives in this study Isotope exchange method Oxygen transfer reaction Mechanism Experimental Setup Preliminary results Conclusions Future work 2

3 Background Coal Addition to Slag Slag Metal e.g. Fe 2 O 3 +C=FeO + CO FeO + C= Fe + CO Direct smelting of iron (DIOS, AISI) Electric arc furnace Slag cleaning of copper making slags 3

4 Background Reaction Mechanism CO/CO 2 C Slag Mass Transfer in Slag MO x Reaction with CO/CO 2 Mass Transfer in Gas Halo Carbon Gasification MO x (s) MOx (s/g) CO (gas) + O (slag) = CO 2(gas) CO 2 (g/s) CO 2 (g/c) CO 2 (g/c)+c = CO(g/C) 4

5 Background Kinetics of Gas-Slag Reaction CO 2(gas) = O (slag) + CO (gas) r ν = r = P ( ) ( ) CO2 a ka P P a k 2 P P 2 P CO CO O CO CO eq CO r k = k 0 ( a ) α a a O r r v a = k ( a ) P = k P s s v a = k ( a ) P = k P 0 α a O CO a CO α a O CO a CO 5

6 Background Kinetics of Gas-Slag Reaction Apparent rate constant k a vs. Slag composition (MO x content in slag, slag basicity) Temperature Gas composition 6

7 Background Effect of Iron Oxide Content CaO-42.5SiO2-15Al2O3, 1773K, Li et al. ka, 10-5 mol/cm 2.s.atm CaO-65SiO2, 1873K, Mori et al. 38CaO-42SiO2-20Al2O3, 1623K, Sun 50CaO-50 SiO2, 1773 K, M. Barati FeOx wt% 7

8 Background Effect of Basicity ka, 10-5 mol/cm 2.s.atm ºC 1600 ºC CaO/SiO 2 M. Barati and K. Coley, Metall. Trans. 36B, 2005, pp

9 Background Effect of Temperature log (ka, mol-o/cm 2.s.atm) FeO=10 wt pct FeO=30 FeO=50 FeO=60 FeO=70 FeO=90 FeO=100 Linear (FeO=100) /T, K -1 M. Barati and K. Coley, Metall. Trans. 36B, 2005, pp

10 Background Effect of Oxidation State of Slag log (ka, mol-o/cm 2.s.atm) FeO=20 wt pct FeO=30 FeO=40 FeO=60 FeO=70 FeO=80 FeO=100 Linear (FeO=100) log (CO 2 /CO) M. Barati and K. Coley, Metall. Trans. 36B, 2005, pp

11 Background Reaction Mechanism (2Fe 2+,2O 2- ) + CO 2 = (2Fe 3+, 3O 2- ) + CO 1. CO 2(g) + = CO 2(ad) 2. CO 2(ad) + e - = CO - 2 (ad) <RDS> 3. CO - 2 (ad) + e - = CO (ad) + O 2-4. CO (ad) = CO (g) 5. 2Fe 2+ = 2Fe e - CO Fe 2+ e - O 2- Fe 3+ CO 2 M. Barati and K. Coley, Metall. Trans. 37B, 2006, pp

12 Background Kinetic Model Rate determining step: CO 2(ad) + e - = CO 2 - (ad) v = kγ ( a ) CO 2 ( ad ) 2 ( ad ) 1. Γ ( C ) CO 2+ ' 2. a = k exp( ) e Φ = F E e Fe Φ κt + Φ E 2 c s F E = E + T γ ln( ) [ Fe ] κ 3+ γ 3[ Fe ] T.H. Wolkenstein, Adv. Catal. Rel. Subj., 1960, vol. XII, pp H. Reiss, J. Phys. Chem., 1985, vol. 89, pp

13 Background Kinetic Model ( E+ E ) ka= k ( C ) exp( Λ Fe ) r(1 + r) 2 RT 3+ Fe γ r = 2+ Fe γ CO ( ) CO Question: 1. Deviation happens at lower Ka range, why? 2. Does model work for other redox couples? 0.5 k a-meas 10 5 (mol.cm -2.atm -1.s -1 ) Li and Ratchev Matsuura et al. Barati and Coley k a-calc *10 5 (mol.cm -2.atm -1.s -1 ) M. Barati and K. Coley, Metall. Trans. 37B, 2006, pp

14 Objectives Find the cause leading to the deviation at low rate constants Measure the rate constant vs. slag composition, temperature and gas composition for different transition metal (Mn, Ti) redox couples Determine general applicability of Barati s model 14

15 Isotope Exchange Method H. J.Grabke, in 1960s G.R.Belton and his associates, using 14 C as tracer isotope in 1970s Nobuo Sano, using 13 C as tracer isotope in 1990s, neglected the natural abundances of 13 C, 1.108% McMaster University 15

16 Isotope exchange Method Oxygen Transfer Reaction Mechanism co 2 co 13 co co 2 co 13 co 2 co 2 o 13 co co 2 M n+ O 2- M n+ M n+ M (n+1)+ O 2- M n+ M (n+1)+ M (n+1)+ M (n+1)+ Slag 13 CO 2(g) + 12 CO (g) = 13 CO (g) + 12 CO2 (g) 16

17 Isotope exchange Method The formulae Measurement is done at gas-slag equilibrium No effect of mass transport 13 CO o ( p 13 ) p 13 2 k a = V 1 co eq ln ART 1 + B ( p ) p eq co co co k a : rate constant B: the CO 2 /CO ratio V: total flowrate T: temperature 17

18 Isotope exchange Method Experimental Arrangement The picture for MS and GC 18

19 Experimental Setup Additional detail M. Barati and K. Coley, Metall. Trans. 36B, 2005, pp

20 Isotope exchange Method The MS and GC 20

21 Experimental Setup Uncertainty in the experimental measurements Difficult to maintain a fixed area High gas flow rate lead to the formation of crater Change in oxygen potential may affect the wetting of crucible that changes the curvature of slag surface Unwanted fluctuations in the gas flow rates 21

22 Experimental Setup Uncertainty in the experimental measurements 22

23 Preliminary results Rate constant vs. gas flowrate 5 ka, 10-5 mol/cm 2.s.atm FeO x -15% Al 2 O 3 T= 1500 CO 2 /CO= Total Gas Flow Rate, ml/min 23

24 Preliminary results Rate constant vs. exposed height k a, 10-5 (mol-o/atm.cm 2.s) CO 2 /CO=0.5 CO 2 /CO=1.0 CO 2 /CO=2.5 CO 2 /CO= Height (cm) 1. Sidewall effect does exist 2. Difficult to control zero exposed height 3. Two choice: a) Multiple height for each set of conditions b) Accept error on very small height 24

25 Conclusions The rate constant deviation is caused by sidewall effect, which is fixed for a given set of conditions and will have a great impact at low rate constant. 25

26 Future work Calibrate the data obtained by Mansoor Barati Measure the rate constant vs. slag composition, temperature and gas composition for Manganese and Titanium redox couples 26

27 Acknowledgement Dr. Ken. Coley Dr. Fuzhong JI Elaine Chen, Yi Chen, Judy Li All friends in MSE 27

28 Thank you! Questions and comments? 28