Optimisation of Power Modulation for Hall-H\'eroult Cells: Process Operability and Constraints as Virtual Energy Storage

TL;DR

This paper explores optimal power modulation strategies for aluminium smelting cells, aiming to enhance profitability and enable renewable energy integration by balancing complex cell dynamics and operational constraints.

Contribution

It introduces a novel optimization approach combining reduced-order and detailed models to determine optimal power modulation profiles under various economic scenarios.

Findings

Optimal line current and ACD profiles identified for different tariffs.

Insights into thermal balance constraints and their impact on operation.

Potential for online control policy development based on results.

Abstract

Aluminium is manufactured through the Hall-H\'eroult process, which is very energy intensive. Power modulation, as an industrial-scale demand-side power management approach, allows aluminium smelters to operate with variable power consumption rates and as such be powered by renewable energy sources. In this way, aluminium smelting cells can be used as a large virtual energy storage to balance power demand-supply and stabilise electrical grids. This paper studies the potential optimal power modulation operating conditions, including time-varying line current and anode-cathode distance (ACD) profiles to maximise the aluminium reduction cell profitability subject to constraints on the cell thermal balance. To deal with the complex cell dynamics which are spatially distributed and multi-timescale, a novel optimisation approach that utilises both reduced-order and detailed models is developed. The results yield insight into the optimal line current and ACD profiles for different power modulation scenarios including the time of use electricity tariff and spot price. These results can form the foundation for further studies into online control policies of aluminium reduction cells.