EMBEDDING SOLAR ENERGY IN ALUMINA USING STEAM REFORMING

McNaughton, R., de la Calle, A., Gardner, W., Stein, W.

Solar energy is an abundant, yet dilute energy resource. In order to incorporate it into an industrial process such as the Bayer process it needs to be concentrated first and converted to a useable form. One such method is the use of solar thermal concentrator to focus the thermal energy to a single point, enabling high temperatures of up to 1000 °C to be achieved. In this form the solar energy can be used to drive endothermic chemical reactions resulting the thermal energy being converted to stored chemical energy. This solar fuel gas can be incorporated into the Bayer process wherever natural gas is currently combusted.

The fuel producing reaction is based on same chemical process used to produce more than 95% of the world’s hydrogen and is therefore an extremely mature technology. Large commercial steam reformers produce more than 200,000 Nm3/h of hydrogen in a single train. The reaction is widely practised commercially for the production of synthesis gases and H2. It is highly endothermic and is generally conducted at temperatures in the range 800-950 °C and pressures in the range 0.5-3.3 MPa. Solar steam reforming is perhaps the most widely studied solar thermochemical option, with extensive on-sun experience by Australian and overseas investigators using a variety of reactor types with solar inputs ranging from 25–600 kWth.

This study examines the suitability of capturing solar energy through a solarised steam reforming processes and subsequently using the solar syngas products in place of other combustible gases for providing thermal energy to the Bayer process. Taking this approach allows a near seamless transition as the process remains virtually unchanged and provides a pathway to lower emission solar based energy sources.

The impact of the variability of the solar resource on the solar reforming process and flow-on impact to the Bayer process is presented and recommendations made to manage the variations. Further, specific parts of the Bayer process are identified that have shown compatibility with the new energy source.