Overview
This project conducted a techno-economic assessment of a range of thermal and alternative storage options for supplying steam to the low temperature stage of refining bauxite to alumina. Thermal storage was considered to directly generate steam while electrical storage was coupled to mechanical vapour compression for upgrading captured water vapour into useful process steam. Both options are intended to convert variable renewable energy input into the consistent steam supply required by the process.
The work of RP1.007 has been extended into RP1.013 Alumina refineries’ next-generation transition (AlumiNEXT™) Project.
Project Details
Thermal and electrical storage technologies were reviewed to identify suitable options that can supply the large quantities of steam at the required temperatures of the process. Data on the performance and costs of the selected technologies was coupled to annual performance predictions for renewable generation for the South-West of Western Australia region, where four alumina refineries are located, to simulate the scale and availability of likely energy inputs to the storage systems. This allowed an integrated model to produce estimates of annual performance for different renewable energy targets to the system.
Optimisation of the overall system design including renewable generation, transmission upgrades, storage system and steam generation equipment allowed indicative techno-economic assessments of the technologies for comparison.
Research Areas
Technology options that were identified as viable for steam generation in the alumina application were thermal energy storage (TES) using molten nitrate salts and electrical compressed air energy storage couple to mechanical vapour recompression (CAES-MVR). Both storage technologies have been operated at similar scales in commercial operations, while other technologies that were reviewed are less developed and they have typically only been applied at small scales.
Outcomes
Lower decarbonisation targets are generally more cost effective and can be largely met with local renewable supply plus some dispersed network renewables. Costs escalate with higher decarbonisation targets, as large capacities of dispersed renewable generation are required to supply demand in poor-quality months (winter). Storage system cost is not the dominant factor in decarbonisation cost, but round-trip efficiency is critical to minimising the generation and supply costs.
Key outcomes
- Both thermal and electrical storage technologies can support 50% and 90% renewable energy targets for steam generation. However, the scale of energy demand requires major increases in regional generation capacity and likely transmission upgrades.
- Directly connected, local generation – preferably using concentrated solar thermal – is favoured to reduce infrastructure costs.
- Land availability for renewable generation will vary by refinery location, affecting the overall cost of supply.
Technology comparison
Thermal energy storage (TES):
- High round-trip efficiency.
- Financially attractive at lower renewable input levels when energy is cheaper.
Mechanical vapour recompression (MVR) with compressed air energy storage (CAES):
- Lower storage efficiency but offset by MVR’s high process efficiency.
- More suitable for higher renewable targets, reducing the cost of new generation and transmission infrastructure.
Overall, storage system costs are generally minor compared to overall infrastructure costs. Minimising the cost of energy supply is likely to dominate decision-making, with the combined storage and steam generation system efficiency being a major factor.
Next Steps
A number of simplifying assumptions were made in this initial study and further progress will require refinement of the system designs with better integration of models with detailed refinery specification and site characteristics.
Published Scientific Papers
- Meybodi MA, Beath AC. Decarbonizing Industrial Steam Generation Using Solar and Wind Power in a Constrained Electricity Network. Solar. 2024; 4(3):471-490.