Background
Aluminum smelting is a highly energy-dependent process which consumes vast amounts of electrical energy, between 2-3% of worldwide electrical usage. Energy costs of aluminum smelting make up around 25% of manufacturing costs to produce primary aluminum (as opposed to recycled). Resistive loss during smelting is the primary source of energy consumption and occurs in the electrolyte layer. By thinning the electrolyte layer the efficiency can be improved but only so far because if the electrolyte layer is too thin the gravitational modes can grow leading to catastrophic short between the carbon anodes and the liquid metal layer.
Technology Overview
By adding an AC component to the current, the gravitational modes can be suppressed, allowing for further decreases in the electrolyte layer, improving the total efficiency, reducing electrical energy consumption and, correspondingly, reducing greenhouse gas emissions.
Benefits
This process has been simulated with industry-standard MHD-Valdis software using a TRIMET 180 kA Al reduction cell model, which resulted in the reduction of the anode-cathode distance by 0.5 mm from 4.3 mm, a 12% reduction. Alternatively, a growing instability can be halted by the application of an AC current component.
By reducing the electrolyte layer by 12%, the total average power is reduced by 4%. If implemented in all Aluminum reduction cells worldwide, energy savings would be roughly 34 TWh, cost savings would be roughly $1Bn, and 13 Mt of CO2 emissions would be eliminated annually.
Applications
Retrofitting of aluminum reduction cells