Thermodynamic Analysis of Solar Water Splitting.pptx

Thermodynamic Analysis of Solar thermochemical Water Splitting system using ceria

1. Thermodynamic and Efficiency A nalysis of Solar T hermochemical W ater / Carbon D ioxide S plitting u sing Ce-Zr Oxide Mixtures Prof. Dr. Shakinaz El Sheltawy Prof. Dr. Nageh Allam Under supervision of : With great support from : Prof. Dr. Seif Fateen Mohamed A.Ganzoury

2. AGENDA 1.Introduction - Energy Challenge Thermochemical H 2 O / CO 2 Splitting Operational C onsiderations in Thermochemical WS and CDS Cycles Metal Oxides in Solar Thermochemical WS and CDS 2 .Objective of the Thesis 3.Thermodynamics Model 4. Results 5.Conclusion 2

3. According to the United Nations Statistics: By 2050: Population is expected to reach 10 billion. The total energy consumption ≈ 28 TW (Current global use ≈ 12 TW). To cap CO 2 to low ppm, we need carbon-free sources. The Road sector gasoline fuel consumption per capita in Egypt 1.1 Energy Challenge http://www.tradingeconomics.com/egypt/

4. 1.1 Energy problem U nequal distribution of these resources of energy resulted in several political problems I t is vital to find alternatives that are clean, affordable and renewable sources of energy Allam,Nageh . ” Materials for Renewable Energy Applications ” AUC.2016 4

5. 1.2 Thermochemical H 2 O/CO 2 Splitting via Metal Oxides We need an oxide material that can lose some of its oxygen without collapse of its crystal structure O 2 H 2 H 2 O Hot Warm 5

6. Advantages Over T raditional M ethods Direct thermolysis has two main problems : It needs a reactor that could stabilize very high temperatures as the process is held at temperatures above 2500 K It is very challenging to separate the products from the product stream at high temperature Chem. Mater. 22 (3), 851–859. 6

7. Advantages Over T raditional M ethods Water splitting process via two-step solar thermochemical cycles : It Requires less temperature in comparison with direct thermolysis . It also produces H 2 /CO and oxygen in two different steps avoiding the need for high temperature separation Prog . Energy Combust. Sci. 29 (6), 567–597 7

8. 1.3 Operational Consideration For reduction reaction : + ½ O 2 It is favorable to decrease the reduction temperature Reduction reaction needs very low partial oxygen pressure to be completed   8

9. 1.3 Operational Consideration For oxidation reaction : + H 2 O  + H 2 T hermodynamically favored at lower temperature and higher oxidation pressure Thus , it is usually carried out in temperatures between 1000 and 1200 K and under atmospheric pressure   9

10. The temperature swing between the two cycles is about 400-500 K in most cases Heat recovery between the two cycles could save a lot of energy required in the process “Heat recuperation” between the two cycles is widely used in order not to reject the heat used in the reduction step 1.3 Operational consideration 10

11. A nother concept was introduced I sothermal cycle 1.3 Operational Consideration 11

12. Reactors Design in Thermochemical WS and CDS Cycles 12 Int J.Hydrogen Energy 2011;36:4757–67

13. Reactors Design in Thermochemical WS and CDS Cycles J Sol Energy Eng 2013;135:31002 13

14. Reactors Design in Thermochemical WS and CDS Cycles Science 2010;330:1797–801 14

15. Reactors Design in Thermochemical WS and CDS Cycles J Sol Energy Eng 2013;135:31004 15

16. 1.4 Metal Oxides in Solar Thermochemical WS and CDS Several metal oxides was used in Solar Thermochemical WS and CDS Using metal oxi d es for water splitting was first introduced in 1970 Fe 3 O 4  3FeO + ½ O 2 3FeO + H 2 O  Fe 3 O 4 + H 2 16 Renew Sustain Energy Rev 2015;42:254–85.

17. 1.4 Metal Oxides in Solar Thermochemical WS and CDS The cycles mainly can be divided into volatile cycles and nonvolatile cycles For volatile cycles, the reduction temperatures used are higher than the boiling point of the metal oxides This cause sublimation of the metal oxide in the reduction process Examples : ZnO /Zn , CdO /Cd , SnO 2 / SnO and GeO 2 / GeO 17 Renew Sustain Energy Rev 2015;42:254–85.

18. 1.4 Metal Oxides in Solar Thermochemical WS and CDS For nonvolatile cycles, the metal oxide does not undergo a phase change during the process Avoid the recombination problem Examples : Ferrites , Ceria 18 Renew Sustain Energy Rev 2015;42:254–85.

19. Ferrite Cycles Ferrites based oxides were widely used in the two-step water splitting cycles Iron oxide has low melting point D oping iron with Zinc, Nickel, Manganese and Cobalt to decrease the reduction temperature T heir reduction temperature was still high (above 1600 K), which results in sintering of the oxide 19 Renew Sustain Energy Rev 2015;42:254–85.

20. Ceria as Oxygen S torage M aterial Ceria, also known as ceric oxide,  cerium oxide or cerium dioxide It is an  oxide  of the rare earth metal  Cerium It is a pale yellow-white powder with the chemical formula CeO 2 Cerium oxide adopts the cubic fluorite structure At high temperatures it releases oxygen to give a  non-stoichiometric defect 20 Philos. Trans. A. Math. Phys. Eng. Sci. 368, 3269–94

21. Ceria as Oxygen S torage M aterial Ceria is popular candidate for thermochemical cycles : High melting point (2800 K) High activity toward gases containing carbon Does not change its crystal structure upon oxygen loss Philos. Trans. A. Math. Phys. Eng. Sci. 368, 3269–94 21

22. Ceria as Oxygen Storage Material Effect of Ceria-dopants on hydrogen production from WS Increasing H 2 Production Decreasing H 2 Production Mg Ca Sc Sr Hf Dy Zr Y Lower ionic radius than cerium ion Higher ionic radius than cerium ion Int J Hydrogen Energy 2011;36:13435–41 22

23. 2. Objective of the Thesis I ntroduce a complete efficiency analysis for Zr-doped ceria with different concentrations of Zr at different operating conditions D etermine the optimum operating conditions for each Zr concentration doped in ceria D iscuss the possibility of attaining higher efficiencies in case of Zr -doped ceria than pure ceria 23

24. 3. Thermodynamic Analysis 24

25. Metal O xide T hermodynamics Thermodynamic data for Ce-Zr mixtures where obtained from Northwestern group 3 Types of Equations was introduced : 1- Oxygen nonstoichiometry ( T, P) 2- C hange in Enthalpy per mole of oxygen release ( δ) 3- Change in Entropy per mole of oxygen release (δ ) Theses data was fitted for different concentration of Zr (5%,10%,15%,20%) in Ceria 25

26. Metal Oxide Thermodynamics For H o For example for 15 % Zr -doped Ceria H o = - 55.45ln(δ ) - 863.97 26

27. Metal Oxide Thermodynamics For 5% Zr -Doped Ceria: For 10 % Zr -Doped Ceria: For 15% Zr -Doped Ceria : For 20% Zr -Doped Ceria :   27

28. Metal Oxide Thermodynamics For 5% Zr -Doped Ceria: For 10 % Zr -Doped Ceria : For 15% Zr -Doped Ceria : For 20% Zr -Doped Ceria :   28

29. Metal Oxide Thermodynamics For Calculating   Chem. Mater. 26, 6073−6082. 29

30. Metal Oxide Thermodynamics 3D fitting Statistics and Machine Learning  Toolbox Number of observations: 178 Root Mean Squared Error: 0.124 R-Squared : 0.975   Adjusted R-Squared: 0.974   30

31. Thermodynamic model for water splitting 31

32. Energy Balance C alculations Q s was taken as 3 kW in all calculations The efficiency analysis was held in two cases : 1- Two-temperature cycle 2- Isothermal cycle 32 Different values of heat recovery effectiveness in the heat exchangers were used to illustrate the impact of heat recovery efficiency on the solar-to-fuel efficiency : Typical heat recovery case : Eg = 90% , Er = 80% Full heat recovery case : Eg =100% , Er = 100% No heat recovery case : Eg =0% , Er = 0%

33. Energy Balance Calculations System held at partial oxygen pressure Po 2 = 10 -2 atm in the reduction chamber ( Two Temp Cycle) System held at partial oxygen pressure Po 2 = 10 -5 atm in the reduction chamber ( Two Temp Cycle) Steam was supplied to the oxidation chamber at atmospheric pressure . 33

34. Results and Discussion 34

35. Two Temperature Cycles Effect of pumping and purifying on the solar to fuel efficiency For Pure ceria T oxd =1073 K 35 Fig 1 : Effect of Q p and Q pur on Solar-to-Fuel efficiency Absence of Q p , Q pur Presence of Q p , Q pur

36. Effect of Ceria Doped with Zr on Solar-to-Fuel Efficiency Normal oxidation temperatures ( T oxd = 1073 k) 36 Effect of Ceria doped with Zr on Solar-to-Fuel efficiency at T ox =1073 K and no heat recovery

37. Effect of Ceria Doped with Zr on Solar-to-Fuel Efficiency 37 Effect of Ceria doped with Zr on Solar-to-Fuel efficiency at T ox =1073 K and typical heat recovery

38. Effect of Ceria Doped with Zr on Solar-to-Fuel Efficiency Chem. Mater. 26, 6073−6082. 38

39. Effect of Ceria Doped with Zr on Solar-to-Fuel Efficiency 39

40. Effect of Ceria Doped with Zr on Solar-to-Fuel Efficiency 40 Effect of Ceria doped with Zr on Solar-to-Fuel efficiency at T ox =1073 K and full heat recovery

41. Effect of Ceria Doped with Zr on Solar-to-Fuel Efficiency 41 Effect of Ceria doped with Zr on Solar-to-Fuel efficiency at T ox =1073, full heat recovery and Q p = 0.

42. Suggested Solutions 42

43. Decreasing T ox 43 Effect of T ox on the Solar-to-Fuel efficiency at T red =1773 K

44. Decreasing T ox 44 Effect of T red on the Solar-to-Fuel efficiency at maximum T ox obtained

45. Increasing δ ox 20% Zr -doped Ceria 45 Effect of δ ox on the efficiency in case of 20% Zr at T red = 1773 K and typical heat recovery at different T ox .

46. Increasing T ox T ox =1600K 46

47. Efficiency Analysis in the Case of Isothermal R edox C ycles Isothermal redox cycles avoid thermal stresses arising from the repeated change from higher to lower temperatures It simplify the reactor design and operation It doesn’t need recuperation heat recovery between the reduced and oxidized metal oxide 47

48. Efficiency Analysis in the Case of Isothermal R edox C ycles 48 Effect of Ceria doped with Zr on solar to fuel efficiency in isothermal redox cycles Change of Δgo with temperature

49. 49

50. Thermodynamic Model for Carbon dioxide splitting 50

51. Results and Discussion 51

52. Effect of Ceria Doped with Zr on Solar-to-Fuel Efficiency 52 Effect of Ceria doped with Zr on the Solar-to-Fuel efficiency at T ox = 1073K and no heat recovery

53. Effect of Changing T ox 53 Effect of T ox on the Solar-to-Fuel efficiency at T red =1773 K

54. Solar-to-Fuel E fficiency at Maximum T ox Obtained 54 Effect of T ox on the Solar-to-Fuel efficiency at T red =1773 K

55. Comparison between WS and CDS 55 Solar-to-Fuel efficiency versus T ox for pure ceria and 5% Zr -doped ceria in WS and CDS cycles ( T red = 1773 k, typical heat recovery) Number of moles of oxidizer (H 2 O, CO 2 ) needed per mole of fuel (H 2 , CO) produced Equilibrium constant for H 2 O and CO 2 splitting reactions

56. Conclusion A thermodynamic model for solar thermochemical H 2 O and CO 2 splitting using Zr -doped ceria materials was developed A complete efficiency analysis for Zr-doped ceria with different concentrations of Zr at different operating conditions was done The optimum operating conditions for each Zr concentration was calculated T he possibility of attaining higher efficiencies in case of Ce-Zr mixtures than pure ceria was proved. 56

57. Conclusion Optimum Operating Conditions ( Typical Heat Recovery) 57 Metal Oxide WS     CDS T ox T red T ox T red Pure Ceria   1100 K   1800 K 1100 k   1800 K 5% Zr -doped ceria   800 K   1800 K 800 K   1800 K 10% Zr -doped ceria   700 k   1800 K 600 K   1800 K 15% Zr -doped ceria   500 K   1800 K 300 K   1800 K 20% Zr -doped ceria   300 K 1800 K ---- ------

58. Conclusion 58 For WS : Operating Conditions Enhancements Compared to Pure Ceria     Isothermal cycles T= 1800 K , Eg =90% 5% Zr -doped ceria increased the efficiency   6 times T ox =1600 K T red =1773 K Typical heat recovery   5% Zr -doped ceria doubled the efficiency       T ox =600 K T red =1773 K Typical heat recovery   15% Zr -doped ceria increased the efficiency   by 23 %

59. Conclusion 59 For CDS : Operating Conditions Enhancements Compared to Pure Ceria     Isothermal cycles T= 1800 K , Eg =90% 5% Zr -doped ceria increased the efficiency   5 times T ox =1600 K T red =1773 K Typical heat recovery   5% Zr -doped ceria tripled the efficiency       T ox =600 K T red =1773 K Typical heat recovery   15% Zr -doped ceria increased the efficiency   by 24 %

60. Future Plans Studying the probability for methane production starting with water and carbon dioxide in one process Build an experimental system for Thermochemical WS in the EML in AUC 60

61. Acknowledgement 61

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