Team publishes in Green Chemistry
The Solar Bayer Alumina Project team confirms that solar could reduce the need for natural gas in the calcination process in alumina refineries.
What we did
In a first-of-its-kind experiment, the team set out to assess and demonstrate the technical feasibility of alumina calcination with direct irradiation via concentrating solar thermal (CST).
The team used a solar vortex transport reactor (see Figure 1 in the full paper for a schematic diagram) and aluminium hydroxide particles as the reactant. During the experiments, we took representative samples from the collected particles in the setting chamber.
After completing the documentation, we can confirm the strong potential to use solar thermal to calcine alumina. This sets the scene for the rest of our work in Program 3. We are not yet able to confirm what the benefits will be at a large scale, but it is plausible that there will be economic gain for alumina refineries.
- Alumina can be calcined with CST radiation. This was demonstrated in a novel 5kW solar transport reactor using radiative fluxes up to 2190 suns.
- Good conversion can be achieved: chemical conversions of up to 96% (aluminium tri-hydrate to alumina oxide) were obtained in this small calciner with a nominal residence time of approximately 3 s and without pre-heat. This shows that good conversion is technically feasible at large scale industrial processes that incorporate pre-heat.
- CST can improve the quality of alumina over existing fossil fuel based processes though a combination of a high heating rate and avoided contamination by combustion products.
- The solar-driven process has the potential to avoid the discharge of combustion-derived CO2 emissions for the calcination stage of the conventional Bayer process, which is typically 165 kg-CO2 per tonne-alumina.
Why are these findings important?
The calcination process of alumina refining with the Bayer process is well suited to the application of CST because it is a highly endothermic process that proceeds at ∼1273 K, which is readily achievable with solar tower technology. In addition, the process is not sensitive to some ingress of air, which raises the possibility that direct irradiation of particles may be achievable without the need for a window to completely seal a solar reactor. Until now, however, the technical feasibility of this had not been assessed.