SOFC and Gas Separation Membranes

How will the future, sustainable energy system look like? The answer to this difficult question depends on a number of technical but also political and socio-economic issues. Besides a massive demand to build up of power supply systems based on renewables, there is a strong need to reduce losses, increase the efficiency of power production processes from fossil fuels and also to consider carbon capture and sequestration (CCS).

Solid oxide fuel cells (SOFCs) convert the chemical energy bound in a fuel directly into electrical energy at temperatures ranging from 600 to 1000 oC, depending on the materials used in the SOFCs. Due to the high efficiencies, the amount of CO2 emitted from carbon containing fuels is smaller compared to conventional energy production technologies based on fuel combustion.

Furthermore, CO2 is formed at the anode side of the fuel cell together with steam, and thus separated from air. Subsequent separation and sequestration of CO2 is therefore easier on a SOFC plant than on conventional power plants based on combustion. Oxide ion conducting materials may be used for gas separation purposes with close to 100 % selectivity.

They typically work in the same temperature range as SOFCs. Such membranes can potentially be used in Oxyfuel processes as well as in IGCC (Integrated Gasification Combined Cycle) power plants for supply of process oxygen, which may reduce cost of carbon capture and storage as dilution of the flue gas with nitrogen is avoided.

Both technologies are very attractive for combination with biomass conversion. A brief status of the Risø DTU activities in the SOFC and membrane areas is presented. Ideas for the use of these technologies in a future more sustainable energy system will be discussed with special emphasis on their combination with biomass conversion and CCS-schemes.