Decarbonizing The Production of Primary Aluminium Using Renewable Resource

Aluminium is the second most widely used metal in the world, with a variety of applications ranging from transportation to food packaging and construction. While many aluminium producers target increased utilization of recycled aluminium to produce rolled aluminium sheets, the need to continuously supply a fraction of pure aluminium persists in order to maintain product quality. In fact, with the continuously expanding industrial activities in many sectors the demand for primary aluminium is expected to increase by 34% in the coming 20 years. Production of primary aluminium is a highly energy intensive process with its smelting contributing by 8% of all worldwide industrial electricity consumption. Molten aluminium (Al(l)) is extracted from alumina via an electrolytic smelting technique called the Hall-Heroult process, the most carbon intensive step in aluminium production. This process requires a huge amount of electricity (~13 – 15 kWh/kg Al) to overcome the strong chemical bond between aluminium and oxygen and relies on the use of a carbon anode as the reducing agent. The electricity source used in the smelting step significantly contributes to the indirect carbon emissions of the process due to the huge multiplication factor associated with the consumption rate of electricity. Direct emissions from the smelting process related to the oxidation of the carbon anode during the Hall-Heroult process are also a major source of CO2 impacting the entire aluminium value chain and considered unavoidable based on current commercial technologies. More than 400 kg of carbon anode is consumed per tonne of aluminium produced, resulting in the formation of more carbon dioxide than aluminium (approximately 1.5 tCO2 / t Al). In this work the utilization of biohydrogen or biogenic char as the reducing agents in the production of primary aluminium is evaluated. In fact, the gasification systems when coupled with waste heat recovery technologies for combined heat and power generation can produce significant amounts of electricity covering the needs of the smelting process, thereby decarbonizing both the direct and indirect emissions of this process. Using a mixed integer linear programming approach via the OSMOSE Lua platform enabled the optimization of this system together with a secondary aluminium production facility where integrating carbon abatement routes such as mineralization of the biogenic CO2 emissions enabled producing net negative aluminium. Products of footprints between -350 and -1500 kg CO2/t Al sheets are attained and significant economic and thermodynamic benefits are possible from the integration.