1. Utilisation of renewable feedstocks in solid oxide fuel cell technology: biohythane
Kleitos Panagi, Christian J. Laycock, James R. Reed and Alan J. Guwy
Sustainable Environment Research Centre, University of South Wales, UK
Introduction: Solid oxide fuel cells (SOFCs) are highly efficient electrochemical devices that convert the energy of a fuel directly into electrical and heat energy. This can be achieved by utilising biomass-derived mixtures. Integration of dark and methane fermentation processes yields a biohythane mixture typically consisting of 10/30/60 vol% H2/CO2/CH4. This process increases the energy yield from waste by approx. 30 % 1.
Aims:
Characterise the performance and fuel processing of the SOFC running on ‘biohythane’ H2/CO2/CH4
Establish the effects of fuel variability
Compare and evaluate the performance of the SOFC with different temperatures
Results:
Dry reforming of methane:
CH4 + CO2 ⇌ 2H2 + 2CO Electrochemical hydrogen conversion:
H2 + O2- → H2O + 2e-
Electrochemical carbon monoxide conversion:
CO + O2- → CO2 + 2e-
Electrochemical methane conversion:
CH4 + O2- ⇌ 2H2 + CO + 2e-
When the cell is operated at specific voltages (0.6 & 0.7 V) both greenhouse gases CH4 and CO2 are fully utilised by the cell to produce electrical energy and synthesis gas (H2 + CO).
Figure 1: Utilisation of biohythane in SOFC at 750 oC. The emissions and current output of the cell are shown.
Dry reforming of methane: CH4 + CO2 ↔ 2H2 + 2CO
When less than 40 vol% CH4 is present the reaction is completed resulting in
When more than 40 vol% CH4 is present, most of the CH4 remains unreacted leaving the
power production via the electrochemical conversion of H2, CO and CH4:
2H2 + O2- → 2H2O + 2e-
CO + O2- → CO2 + 2e-
CH4 + O2- → CO + 2H2 + 2e-
electrochemical oxidation of methane to contribute to power production:
CH4 + O2- → CO + 2H2 + 2e-
Figure 2: The effect of fuel variability on I-V curves at 750 °C and corresponding fuel cell power curves plotted on the secondary axis.
Conclusions: Renewable feedstocks such as biohythane can be utilised by SOFC, to simultaneously yield energy and chemical products. At specific operating conditions, both greenhouse gases CH4 and CO2 are fully utilized by the cell. Performance and fuel processing are sensitive to fuel composition and are significantly affected when the CH4 content in the mixture is increased. The cell operating temperature has a major impact on the performance of the cell.
Reference: 1. Guwy, A.J., et al., Bioresource Technology, (18): p
Fig.3 demonstrates that at higher temperatures, activation and concentration losses decrease because the fuel and the oxidant have more energy to pass through the electrodes and the reaction rate is higher leading to increased power production.
Figure 3: I-V and power curves at different temperatures.
FLEXIS is part-funded by the European Regional Development Fund (ERDF), through the Welsh Government. Ariennir yn rhannol gan Gronfa Datblygu Rhanbarthol Ewrop drwy Lywodraeth Cymru.
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