Testing SOFCs with Blends of Hydrogen and Methane

Transcription

1 Testing SOFCs with Blends of Hydrogen and Methane Gerhard Buchinger 1,2, Thomas Raab 1, Stefan Griesser 1, Vincent Lawlor 1, Jürgen Kraut 3, Renate Hiesgen 3, Dieter Meissner 1 1 Upper Austrian University of Applied Science 2 University of Leoben 3 University of Applied Sciences Esslingen 1

2 2 slide 2 CONTENT Motivation Experimental setup Experiments with pure methane Experiments with blends of hydrogen and methane at 850 C Experiments with blends of hydrogen and methane at 900 C

3 3 slide 3 Motivation for the Experiments Natural gas: already existing supply system SOFC: promises higher efficiency for converting the fuel to electricity Question: What working condition give the highest stability and what is the maximum allowed methane concentration under these conditions?

4 4 slide 4 Experimental Setup Microtubular SOFC with about 2.5 mm outer diameter and 50 mm length, Electrolyte stabilized cells (ESC) made of Yttria Stabilized Zirconia (YSZ), Cathode: Lanthanum-Strontium Manganite (LSM), silver wires and silver ink as contacts, Anode: Nickel-YSZ-Cermet with 5 % CeO 2, nickel mesh and wires as contact.

5 5 slide 5 Experimental Setup Fuel supply Humidifier Controll Unit Water trap Flow-Controller Potentiostat with Impedance Analyzer Oven with fuel cell Gas Chromatograph

6 6 slide 6 Experiments with Dry Methane Working temperature: 900 C Flow Conditions: 50 ml/min H 2 or CH 4 In order to get refererence values, the cell was operated for about 5 hours with hydrogen. After this, pure methane was used. The power output dropped after 10 h dramatically and post mortem analyses showed massive carbon depositions.

7 SOFC Performance with Pure Methane 7 slide P [mw/cm²] switching from hydrogen to methane Time [minutes]

8 Experiments with Dry Blends of Hydrogen and Methane at 850 C 8 slide 8 Working temperature: 850 C Flow Conditions: 50 ml/min dry H 2 or CH 4 / H 2 blends The tested methane concentrations have been 0, 5 Vol%, 10 Vol% and 20 Vol% and the cell was operated under constant current. In order to get reference values the cell was driven for about 90 hours under hydrogen atmosphere. After this, the methane concentration was increased step by step. A stable performance was found with 10 Vol% methane in the observed time period, with 20 Vol% a fast the power output decreased fast.

9 Reference: Performance Using Dry Hydrogen 9 slide P [mw] t [min]

10 10 slide 10 Compairing of performances over time with dry blends P [mw] t [min] H2 after stabilizing 5 % methane 10 % methane 20 % methane

11 11 slide 11 IS analysis with hydrogen after stabalizing Z im [O hm cm 2 ] 1.80E E E E E E E E E+00 anode part cathode part 0.00E E E E E E E E E E E E E+01 Z re [Ohmcm 2 ] H2 + air 3500 min H2/N2 + air 3500 min H2 + air/n min

12 12 slide 12 IS analysing after 20 % methane test 3.40E E+01 Z im [Ohmcm2] 2.40E E E E E+00 Third process: diffusion problems? -1.00E E E E E E E E E+01 Z re [Ohmcm 2 ]

13 Is there a possibility to regenerate cells by using pure hydrogen? 13 slide P[mW] t [min] Only a part of the experiment is shown because of problems with the data logging. After 12 more hours the power output was nearly zero.

14 Experiments with Blends of Hydrogen and Methane at 850 C 14 slide 14 Working temperature: 850 C Flow Conditions: 20 ml/min H 2 or CH 4 / H 2 blends with 66,6 % moisture, methane concentrations of around 27 Vol%. In order to get refererence values the cell was operated for about 20 hours.

15 15 slide 15 Performance of the SOFC with wet hydrogen at 850 C P [mw] t [min]

16 Results of Experiments with Blends of Hydrogen and Methane at 850 C 16 slide 16 Operating the cell with 66,6 % moisture in hydrogen was possible. With 27 Vol% methane the cell only worked stable for 40 min. After this, the power decreased to zero within 2 hours!

17 17 slide 17 Experiments with Blends of Hydrogen and Methane at 900 C Working temperature: 900 C, flow Conditions: 50 ml/min H 2 or CH 4 / H 2 blends with 66,6 % moisture. The tested methane concentrations have been 0, 25 Vol%, 50 Vol% and 75 Vol% In order to get refererence values the cell was operated with hydrogen for about 14 hours. Up to 75 % methane in the fuel did not cause higher degradation than that found with hydrogen and no carbon deposition was observed. But big power loss with 2/3 water in hydrogen at the beginning could be found in contrast to the experiment at 850 C.

18 18 slide 18 Relative poweroutput of different CH 4 /H 2 blends over time 120 relative Power after stabalizing with hydrogen [% t [min] H2 after stabalizing 25 % methane 50 % methane 75 % methane

19 19 slide 19 IV-curves with the different methane concentrations relative poweroutput [%] I [ma] 66 % H2O in H2 after stabalizing 25 % methane 25 % methane after observed time period 50 % methane 50 % methane after observed time period 75 % methane 75 % th ft b d ti i d

20 Gas Chromatography Investigations 20 slide 20 No high reforming activity of the tested anode was found! With low water concentrations CO is found in higher concentrations than CO 2! The methane consumption/reforming has decreased with cell degradation and the amount of CO 2 has surpassed that of CO.

21 21 slide 21 Conclusions Using pure methane in our cells is not possible! Adding water allows higher methane concentrations! Increasing the temperature from 850 C to 900 C had positive effects for the stability when using the hythane.

22 22 slide 22 Questions HOW DO DIFFERENT TYPES OF CELLS (ASC OR ESC) HANDLE DIFFUSION PROBLEMS OF THICK ANODES CAUSED BY CARBON DEPOSITION? WHAT IS THE INFLUENCE OF DIFFERENT TYPES OF ANODE DESIGNS (MORE LAYER ANODES)?

23 23 slide 23 Power Output and Fuel Utilization fuel utilization [%] P [W] Flow Hydrogen [ml/min]

24 24 slide 24 Outlook Tests with different cells and short stack experiments.

25 25 slide 25 References K. Kendall et. al., Journal of power sources 106 (2002), C. Finnerty et. al., Journal of power sources 86 (2000) G.J. Saunders et. al., Journal of Power Sources 106 (2002),