A systemic study for decarbonizing secondary aluminium production via waste heat recovery, carbon management and renewable energy integration

Abstract

Secondary aluminium production relies on natural gas to transform both primary and recycled aluminium into semi-fabricated products, leading to significant atmospheric emissions, energy losses, and resource consumption. Despite the potential for waste heat recovery from stacks, casting water, and ancillary systems, wide-ranging temperature levels of waste heat produced complicate process integration. This work presents a systemic approach to enhance waste heat recovery, reduce fossil fuel consumption, integrate renewable energy resources, and use low-grade waste heat from a secondary aluminium plant to supply the heating requirements of a neighboring urban system. The goal is to highlight the role of process integration in decarbonizing and diversifying the industry’s energy requirements. A comprehensive techno-economic analysis evaluates decarbonization strategies, including, carbon capture, use, and sequestration; biomass energy conversion; oxycombustion furnaces; power-to-gas units; combined heat and power; heat pumps and seasonal storage units, considering energy prices, city demands, and seasonal variations. A systematic framework is employed to determine the most suitable decarbonization routes, while maintaining operational and financial feasibility. Results show that, carbon capture alone can only halve current CO₂ emissions (to 100 kg_CO2/t_Al). Meanwhile integrated renewable electricity and biomass options achieve −200 kg_CO2/t_Al with 27% lower total energy and 40% less biomass use than biomass-only configurations. Power-to-gas systems without biomass import reduce emissions by only 80%, making them also unsuitable for net-zero targets. Finally, electricity self-generation of 30% of the overall power consumption can be achieved if the exothermic reaction enthalpy of carbon mineralization is recovered for various applications, such as biomass drying, steam generation, amine regeneration, and district heating. These findings highlight the need for a holistic approach that optimizes resource integration, minimizes emissions, and ensures long-term sustainability in secondary aluminium production.