Advancing Biogas Utilization through Fuel Flexible SOFC

Biogas provides an excellent means to convert waste to energy. It is an important technology widely applied in rural India with many significant installations also in the UK and Europe. Currently electricity is generally produced from biogas through thermal conversion; however, the electrical efficiency of this process is low. Converting biogas to electricity via fuel cell technology offers significant increases in efficieny, perhaps a factor of 2, and hence is a highly desirable technology. Some biogas installations do exist utiliing molten carbonate fuel cell technology; however, it is widely considered that Solid Oxide Fuel Cell Technology is the most promising future technology due to its much higher power density and its applicability to a wide range of scales. Here, we seek to improve the performance and durability of SOFC fuel electrodes for operation in biogas.

Biogas is largely a mixture of CO2 and methane with quite large impurity contents of hydrogen sulphide. In this study, we investigate the performance and durability of some different SOFC concepts in fuel gas compositions directly relevant to biogas operation. The first strategy investigated will be to develop new perovskite and related materials for application as SOFC anodes that are resistant to coking and sulphur degradation. The second strategy to be investigated, relates to the utilisation of proton conducting perovskite to protect Ni and other electrocatalysts from coking and degradation. These and more conventional electrodes will be studied through sophisticating imaging techniques and electrochemcal performance testing. Promising concepts will be scaled up into significant cells, i.e. >10cm2 and rigourous testing performed. Test cells will be made and evaluated under different gas mixes probing both operation on startup in biogas and on prolonged operation utilising anode exhaust recirculate (containing steam and additional CO2) for internal reformation. Durability will be assessed up to 1000 hrs in appropriate biogas reformates and the degree of Sulphur scrubbing required, if any, assessed. Overall we seek solutions that could be applied to multi-kW scales of relevance decentralised and isolated operation.

The UK will lead imaging and modelling, new anodes and performance testing, whereas India will lead proton conducting cermets and cell fabrication and scale up; however all activites involve significant cross-national activity.

Two project workshops will be held in the UK and two in India and these will be linked to training events and outreach meetings open to the wider community. Each researcher will spend at least one month working in partner country laboratory on joint activity.

The world faces an immense challenge to address the energy demands of emerging economies whilst not further increasing anthropogenic CO2 emissions. A key approach is to change from regarding waste as a problem that needs to be solved to an opportunity to harness essentially free energy. Conversion of suitable waste streams to biogas offers a very promising route to heat or electricity. Unfortunately much of the available energy is lost when electricity is produced due to inefficient conversion. Combining biogas production with fuel cell conversion can greatly increase the amount of electricity produced from a given volume of waste and hence is a very attractive future technology.

Biogas produced from the anaerobic digestion of manure and other organic wastes in small-scale digestion facilities and is used in over two million households in India, providing an affordable and effective energy source to communities that have great need. In the UK, agriculture generates of the order of 3 million tonnes per annum of wet animal slurries and manures and it is estimated that even with 50% utilisation 1.1TWhr could be generated from these sources alone.

Some biogas fuel systems do exist utilising MCFC technology; however, SOFC technology offers improved power densities and better scalability. Biogas/SOFC is widely recognised as an important direction for future R&D. The work described in this project will improve performance and durability and most importantly will allow simpler systems to be developed opening up important new markets especially for the grid isolated rural communities. Delivery of new technologies which provide new capabilities, not achievable with existing technologies, is key to rapidly ramping up their uptake and will firmly establish the new fuel cell industry.

The likely impact of the project is significantly enhanced by the complimentary strengths of the UK and India partners. This project brings together a very significant capability involving leading edge capability in new materials, imaging, processing and testing.