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.
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.
Identified Pathways
Technology options that were identified as viable for steam generation in the alumina application were thermal storage using molten nitrate salts (TES) 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
Assessment of the alternative options for thermal and electrical storage found that either technology type could deliver the targets of 50% and 90% renewable energy input to steam generation. However, the scale of the industrial energy use is large and would require significant expansion in the generation capacity of the region and is likely to result in additional costs for transmission upgrades. Generation that is local to the refineries and can be directly connected is therefore favoured and an additional preference for the use of concentrated solar thermal to directly provide heat for thermal storage was identified. The availability of suitable land to host the generation facilities will depend on individual refinery locations, but it is likely that generation will be more widely dispersed, and this will have an impact on the cost of supply to the storage system.
A key difference between the technologies is that TES has a very high round-trip efficiency and at lower renewable inputs where energy can be provided cheaply this is likely to be a financially attractive method of introducing more renewable content to the refineries. CAES has a lower efficiency and is less cost-effective as a storage, but the high efficiency of MVR results in lower input of renewable energy and at high renewable targets this appears to be a preferred option to reduce the cost of new generation and transmission infrastructure. In most cases the cost of the storage systems is a minor component of the overall cost of new infrastructure and it is minimising the cost of energy supply that 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.
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