System dynamics analysis of strategies to reduce energy use in aluminum-intensive sectors

Aluminum is one of the most widely used materials in industry, with applications in buildings, vehicles, aircraft, and consumer products. Its ubiquity is also on the rise: aluminum is beginning to supplant steel in... [ view full abstract ]

Aluminum is one of the most widely used materials in industry, with applications in buildings, vehicles, aircraft, and consumer products. Its ubiquity is also on the rise: aluminum is beginning to supplant steel in lightweight vehicles and aircraft, and is used in many “green” or LEED-certified buildings.  Although aluminum tends to be highly recycled, particularly by manufacturers of aluminum products, the sector as a whole is still far from a closed system.  As a result, the increase in aluminum consumption also means an increase in primary aluminum production – an energy-intensive process – and an increase in consumption of the raw material bauxite, which in the U.S. is almost entirely imported.  Our objectives for this study are to identify and analyze aluminum sector technologies and practices that reduce the energy required to manufacture aluminum products and reduce U.S. dependence on imported aluminum and bauxite.

To accomplish these objectives, we will develop a system dynamics (SD) model of aluminum production, use and recycling in key application areas, including aerospace, ground vehicles and consumer products.  The model will cover the entire aluminum supply chain as it exists in the U.S., from bauxite importing and refining, to the manufacture of products, to the product use phase and end-of-life processing steps.  Aluminum flows throughout the model will be determined by the annual domestic demand for each application area as well as demand projections that extend to 2030.  Energy consumption will be tracked based on the flows of aluminum through each step of the supply chain.

Using the SD model, we will evaluate several technologies and practices that have the potential to reduce energy consumption and reliance on imported bauxite.  These include implementation of advanced primary aluminum production technologies, increased recycling within and between application areas, increased material efficiency and increased product lifetimes.  Each of these strategies results in short term reductions in energy use, and every strategy except the advance production technologies will also reduce the need for imported bauxite. 

This model differs from other SD models previously built to study aluminum stocks and flows in two key areas: alloy recycling and product lifetimes.  Aluminum recycling is frequently complicated by the need to maintain quality of many different alloys, especially in aerospace applications.  This necessitates scrap sorting and product disassembly to avoid contamination; advanced recycling processes of this type are one of the strategies to be evaluated.  Product lifetime similarly complicates aluminum recycling, as products with longer lifetimes yield smaller recycling streams compared to disposable or short lifetime products, such as soda cans.  When these additional complexities are accounted for in the SD model, a more realistic idea of the short term and long term impacts of the various strategies can be captured, as can any potential synergies and trade-offs between the strategies.  Results of the analysis will indicate which strategy, or combination of strategies, yields the lowest cumulative energy consumption and bauxite consumption required to satisfy current and future demand for aluminum products.