CO2 Capture and Management Strategies for Decarbonizing Secondary Aluminium Production

The production of aluminium largely depends on the use of fossil fuels, resulting in the emission of significant amounts of greenhouse gases. As the aluminium industry is working towards decreasing its environmental burdens, the elimination of direct emissions from the remelting step becomes increasingly important. This research presents opportunities for decarbonizing secondary aluminium remelting and rolling via optimized carbon capture and abatement routes. Various carbon capture and management strategies for secondary aluminium production sites are developed and evaluated. To this end, process integration and optimization techniques following a mixed integer linear programming (MILP) approach are applied. A blueprint of an aluminium plant is developed, and the integration of several carbon capture and management technologies is modelled. The studied capture options include oxy-combustion, amine-based absorption, membranes, structured solid sorbents, and cryogenic beds. Once captured, the concentrated CO2 gas stream can be pressurized for pipeline transport or injection into basaltic rock formations, transformed into synthetic natural gas, mineralized into cement additives, or used to produce plastic monomers. A systemic approach was adopted to compare these options in terms of multiple performance indicators. It was found that, more than 90% of the emitted CO2 can be efficiently captured and utilized. Moreover, additional revenue from cement additives (produced via mineralization), or reduced expenses (due to less CO2 tax) via injection routes results in a net negative change in operating expenditures of the plant with comparison to continuously emitting the base flows of fossil CO2. While methanation provides a potential defossilization route when coupled with the use of renewable electricity, it comes at the expense of CO2 upgrading costs currently higher than buying cheap (subsidies) fossil fuel. Moreover, production of value-added chemicals (olefins) through CO2 capture was also found more expensive from a system point of view compared to today’s fossil-based prices of these commodities. Among the evaluated capture technologies oxyfuel combustion was found specifically promising in the case of secondary aluminium production due to its improved energy efficiency and high technology readiness levels which drive lower costs of application. All these capture and utilization systems are almost three times cheaper than importing green hydrogen for use in aluminium furnaces, a potential solution still under experimental validation in the aluminium sector. Finally, in case of CO2 transportation for injection, logistical challenges are a pressing issue for industries looking to reduce their direct emissions, especially in land-locked countries such as Switzerland.