Absorption of Nitric Oxide from Flue Gas using Ammoniacal Cobalt(II) Solutions by Hesheng Yu Supervisor: Dr. Zhongchao Tan

Transcription

1 Absorption of Nitric Oxide from Flue Gas using Ammoniacal Cobalt(II) Solutions by Hesheng Yu Supervisor: Dr. Zhongchao Tan 1

2 Outline 1. Background 2. Selection of Absorbent 3. Determination of Equilibrium Constants 4. Kinetic Study 5. Effect of Oxygen and Absorbent Regeneration 6. Mass Transfer in Industrial Gas-Liquid Contactors 7. Conclusions 2

3 1. Background 3

4 Nitrogen Oxides (Mt) Mobile Stationary NOx Emissions from Conventional Power Plants in U.S., Year 4

5 Nitrogen Oxides Facts Formula Name Nitrogen Valence Properties N 2 O nitrous oxide 1 colorless gas water soluble NO N 2 O 2 nitric oxide dinitrogen dioxide 2 colorless gas slightly water soluble N 2 O 3 dinitrogen trioxide 3 black solid water soluble, decomposes in water NO 2 N 2 O 4 nitrogen dioxide dinitrogen tetroixe 4 red-brown gas very water soluble, decomposes in water N 2 O 5 dinitrogen pentoxide 5 white solid very water soluble, decomposes in water 5

6 NOx Hazards & Threats: Tropospheric Ozone Acid Rain 6

7 NOx Control Technologies NO x Control Technologies Fuel Switching (not very realistic) Combustion Modification (20-70%) Reduce nitrogen content Less Excess Air Staged combustion Flue gas recirculation Low-NOx burners Water/steam injection Selective catalytic reduction Flue Gas Treatment (FGT) Required to meet increasingly stringent (<15ppm) emission regulation Selective non-catalytic reduction Combined plasma photolysis Adsorption Wet scrubbing (cost-effective) 7

8 Absorbent for Wet Scrubbing Strong Oxidant for conversion NO into NO 2 ClO 2 /NaClO 2 KMnO 4 O 3 Absorbent H 2 O 2 Reagent for formation of a nitrosyl complex H 2 O 2 / with NH 3 FeSO 4 Fe(II)-EDTA Advantages of Ammonical Cobalt(II) Complexes: Fast reaction Positive effect of oxygen on NO absorption Easy regeneration Potential to simultaneously remove NO and SO2 Environmentally friendly by-products Nitrate and nitrite Ammoniacal Cobalt(II) Ions 8

9 Ammonia Cobalt(II) System (with concentrated ammonium) Reaction Number Co(H 2 O) NH 3 Co(NH 3 )(H 2 O) H 2 O (1-1) Co(NH 3 )(H 2 O) NH 3 Co(NH 3 ) 2 (H 2 O) H 2 O (1-2) Co(NH 3 ) 2 (H 2 O) NH 3 Co(NH 3 ) 3 (H 2 O) H 2 O (1-3) Co(NH 3 ) 3 (H 2 O) NH 3 Co(NH 3 ) 4 (H 2 O) H 2 O (1-4) Co(NH 3 ) 4 (H 2 O) NH 3 Co NH 3 5 (H 2 O) 2+ + H 2 O (1-5) Co(NH 3 ) 5 (H 2 O) 2+ + NH 3 Co(NH 3 ) H 2 O (1-6) NH + 4 NH 3 + H + (1-7) Reactive Complexes 9

10 Percentage (%) Ammonia - Cobalt (II) System for different ph values at T=30 o C Co 2+ A=NH 3 [NH 4+ ] = 2mol L -1 CoA 6 80 Co2+ 70 [CoA] [CoA2]2+ [CoA3]2+ [CoA4]2+ [CoA5]2+ CoA 4 30 [CoA6] CoA CoA ph value ph =7.5 10

11 Reactions of NO Absorption into Penta- and Hexaamminecobalt(II) solutions 2NO + 2[Co NH 3 6 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co NH 3 (1-8) 2NO + 2[Co NH 3 5 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co 4+ (1-9) Light Yellow Pink or Red 11

12 2. Selection of Absorbent 12

13 Experimental Setup for Absorbent Selection Testo 350 XL Valve 4 Valve 5 Valve 2 Valve 3 Column Reactor Connector Mixer Water Jacket Valve 1 Mass flow meters Beaker Thermostatic Bath N 2 O 2 NO Scrubbing bottle 13

14 Comparison of NO Reduction between Different Absorbents Hydrogen Peroxide Fe(II)-EDTA 14

15 NO Removal (%) Effect of Temperature on NO Removal Efficiency Inlet flow rate = 500ml/min, NO = 500 ppm, O2 = 5.0%, ph = 10.5, Cobalt (II) = 0.06 mol L Time (min) 15

16 3. Determination of Equilibrium Constants 16

17 Laboratory Setup for Equilibrium Study 17

18 Picture of Main Section of Testing Rig 18

19 Validation of Complex Reactivity NO Absorption Curve 99.65% 19

20 Validation of Complex Reactivity Colour Change 2NO + 2[Co NH 3 6 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co NH 3 (3-1) 2NO + 2[Co NH 3 5 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co 4+ (3-2) Light Yellow Pink or Red 20

21 Brief Calculation of Equilibrium Constants 2NO + 2[Co NH 3 6 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co NH 3 (3-1) 2NO + 2[Co NH 3 5 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co 4+ (3-2) [Co(NH 3 ) 5-6 ] 2+ e is given by mass balance of cobalt(ii) where a w = water activity; f NH3 = the activity coefficient of the ammonia; Gm = molar flow rate, mol s -1 K NO 5 = the equilibrium constant of Reaction 3-1, L 3 mol -3 ; K NO 6 = the equilibrium constant of Reaction 3-2, L 3 mol -3 ; P T = total pressure, atm; y in, y out = NO concentration at inlet and out, ppm; η = NO removal efficiency 21

22 Equilibrium Constants of Reactions (3-1) and (3-2) 5 lnk NO = T (R2 =0.994) (3-3) 6 lnk NO = T (R2 =0.970) (3-4) Rewritten as, 5 = exp ( ) (3-5) T K NO 6 = exp ( ) (3-6) T K NO where K NO the equilibrium constant of Reaction 3-1, L 3 mol -3 ; K NO the equilibrium constant of Reaction 3-2, L 3 mol -3 ; T --- temperature, K 22

23 4. Kinetic Study 23

24 Double-Stirred Tank Reactor 24

25 Laboratorial Setup for Kinetic Study 25

26 Picture of actual laboratorial setup for kinetic study (a) flue gas simulation system (b) double stirred tank section 26

27 Calculation Scheme 2NO + 2[Co NH 3 6 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co NH 3 (4-1) 2NO + 2[Co NH 3 5 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co 4+ (4-2) According to film theory and enhancement factor for parallel reactions, the rate of NO absorption into ammoniacal cobalt(ii) solutions, presented in Reactions 4-1 and 4-2, can be described as follows: N NO = ( 1 Hk G D NO m + 1 k mn 5 B n 5 c m 1 NOi + 2 ) 1 c NOi (4-3) p + 1 k pq 6 B q p 1 6 c NOi where N NO --- NO absorption rate, mol m -2 s -1 ; H --- Henry Law constant, L atm mol -1 ; k G --- gas-phase mass transfer coefficient, mol s -1 m -2 atm -1 ; D NO --- molecular diffusivity of NO in liquid phase, m 2 s -1 ; m, n, p, q, reaction orders with respect to reactant; k --- reaction rate, unit is dependent upon reaction orders 27

28 Determination of Reaction Order with regard to NO N NO = ( 1 Hk G D NO m + 1 k mn 5 B n 5 c m 1 NOi + 2 ) 1 c NOi (4-3) p + 1 k pq 6 B q p 1 6 c NOi m=p=1 can be given by the obvious linear relationship between N NO and c NOi as shown in the figure. Therefore, substituting of m=p=1 into Eq. 4-3 gives k 5 1n B n 5 + k 6 1q B q 6 = c NOi N 1 NO Hk G D NO 2 (4 4) Y 28

29 Determination of Reaction Orders with regard to Penta- and Hexa-amminecobalt(II) Solutions The value of reaction rate decreases with temperature 29

30 Analysis of Reaction Orders with respect to Penta- and Hexaamminecobalt(II) Solutions c NOi 1 N NO Hk G D NO 2 k 2 6 B 6 = k 2 5 B 5 (4 5) c NOi 1 N NO Hk G D NO 2 k 2 5 B 5 = k 2 6 B 6 (4 6) Y 30 (a) (b)

31 5. Effect of Oxygen and Regeneration 31

32 Laboratory Setup 32

33 Effect of Oxygen on NO Absorption into Ammonical Cobaltous Solutions 5.6% 2.1% 0% 8.7% 33

34 Proposed Scheme for NO Absorption with Presence of Oxygen Hentaaminecobalt(II) NO Cobalt peroxynitrito O 2 Nitrosylpentaamminecobalt(III) (1b) μ-peroxo-bis[pentaamminecobalt(iii)] (2b) 2b O 2 NO O 2 Pexaaminecobalt(II) Cobalt peroxynitrite intermediate Nitrate and/or Nitrite 34

35 Proposed Scheme for NO Absorption with Presence of Oxygen 2NO + 2[Co NH 3 6 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co NH 3 (5-1) 2NO + 2[Co NH 3 5 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co 4+ (5-2) Conclusion: For continuous feed of flue gas into ammoniacal cobalt(ii) system, Reactions 5-1 and 5-2 are in fact irreversible with the existence of oxygen. The presence of oxygen significantly improves the NO absorption into ammoniacal cobaltous complexes. The final NO absorption amount into the ammoniacal absorbent is entirely dependent upon the original absorbent concentration regardless of nitric oxide and oxygen concentration. This finding corresponds with our experimental results. 35

36 Regeneration Tests of Different Additives at Various Temperatures Without KI at RT With KI at RT 36

37 Regeneration Tests of Different Additives at Various Temperatures Without KI at 52 oc With KI at 52 oc 37

38 Performance of Combination of AC and Na 2 S 5 O 8 38

39 Performance of Combination of AC and KI 39

40 6. Mass Transfer in Industrial Gas-Liquid Contactors 40

41 Experimental Setup of the Gas-Liquid Contactor System 41

42 Effect of Impeller Speed on Degassing Efficiency in GIAT and CSTR CSTR: conventional stirred tank reactor GIAT: gas-inducing agitated tank 42

43 Effect of Purge Nitrogen Flow Rate on Degassing Efficiency in CSTR and BC CSTR: conventional stirred tank reactor BC: bubble column (Porous media) (Multiorifice) 43

44 Degassing Efficiency of the Semi-batch Degasser at Different Conditions 44

45 7. Conclusions 45

46 Conclusions: 2NO + 2[Co NH 3 6 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co NH 3 (3-1) 2NO + 2[Co NH 3 5 ] 2+ Co NH 3 5 N 2 O 2 NH 3 5 Co 4+ (3-2) 5 lnk NO = T (R2 =0.994) (3-3) 6 lnk NO = T (R2 =0.970) (3-4) The reaction rate constants of Reactions 3-1 and 3-2 are calculated based on the enhancement factor derived for gas absorption accompanied by parallel chemical reactions. Both reactions are first order with respect to NO and first order with respect to liquid absorbent. The forward reaction rate constants of Reactions 3-1 and 3-2 are and L mol -1 s -1, respectively at K, and increase to and L mol -1 s -1, respectively at K. 46

47 Conclusions: Proposed Scheme for NO Absorption with Presence of Oxygen Hentaaminecobalt(II) NO Cobalt peroxynitrito O 2 Nitrosylpentaamminecobalt(III) (1b) μ-peroxo-bis[pentaamminecobalt(iii)] (2b) 2b O 2 O 2 Pexaaminecobalt(II) NO Cobalt peroxynitrite intermediate Nitrate and/or Nitrite 47

48 Conclusions: Liquid-phase mass transfer coefficient for different reactors Conventional stirred tank reactor k L a C = 1.59 N I N cd U G 0.93 ( d T d I ) Gas-inducing agitated tank k L a GI = P c V L ( Q I d T 2 )0.692 ( s d T ) Bubble column with efficient gas sparger k L a B = 1.091U G 0.8 Bubble column with simple gas sparger k L a B d T 2 D L = 0.6( ν L ) 0.5 ( gd T 2 ρ L ) 0.62 ( gd 3 T D 2 L ν ) ε G L σ L 48

49 Acknowledgement Dr. Zhongchao Tan Dr. Mark J.Rood Dr. Xianguo Li Dr. John Z. Wen Dr. Eric Croiset Dr. Qunyi Zhu Dr. Guangyuan Xie Dr. Sudong Yin Grace Pan Chao Yan Harry Lei Ke Zhang Zhe Li Stephen Kuan Raheleh Fang Liu APRIL GROUP MECHANICAL ENGINEERING 49

50 APRIL GROUP MECHANICAL ENGINEERING 50