Scientific Events

What is the role of materials in today’s global economy as we deal with pressures from a growing population and a climate emergency? Aluminum production and usage helps provide food, shelter, health, transportation, and entertainment to the world. Achieving these goals in a “sustainable” manner dictates that our materials “will impact positively on society’s current needs and have no negative effects on future generations to enjoy the same benefits.’ Life cycle analyses (LCA) of materials and products generally rate aluminum’s sustainability positively from an accounting of the energy and usage costs through the product lifetime. While plastic packaging, in particular, receives well-deserved bad press for polluting our world, it is necessary for aluminum suppliers and users as well to use our energy-intensive metal wisely. The talk will review the current production and carbon emissions footprint for primary aluminum and the role of recycling and secondary operations in the industry. Note that the analysis will take into account the sources of energy (renewable or fossil fuel) in different parts of the world. What is the current state of aluminum primary production? What adaptations are taking place?What is the prospect for new aluminum production technology?How do buildings, transportation and packaging markets stand in regard to production, use, re-use and recycling?What are the roadblocks to maximizing re-use and recycling? possible approaches to close them?Is ‘Green aluminum’ an achievable target? [more]

Besides their ubiquitous use in load-bearing structures, metals also possess qualities of energetic materials. Lithium, for example, is a common fuel in batteries, while aluminum is frequently added to solid rocket propellants and used in pyrotechnics. At high temperatures, metal powders can be burned in air in a similar way to hydrocarbon fuels, releasing chemically stored energy as sensible heat. Contrary to hydrocarbon combustion, however, the main reaction products are solid oxide particles that can, in principle, be retrieved from the exhaust fumes. This amenability to oxide sequestration has stimulated the idea of harnessing metal powders as recyclable energy carriers which are burned, retrieved and, subsequently, recharged by a reduction process based on clean primary energy. Conceptually, the metal powders are akin to high-temperature batteries, serving as a means to buffer the large spatial and temporal intermittency associated with renewable energy sources. Motivated by the potential use of metal powders as recyclable fuels, we qualitatively discuss the physical and chemical processes involved in the combustion of a single metal particle and of metal dusts, respectively. Subsequently, a population balance model for predicting the size distribution of the oxide smoke precipitating in the vicinity of a single burning aluminum particle is presented. Here, we specifically focus on the kinetic rates that control the phase transitions and smoke dynamics, integrating recently developed detailed kinetics for gas phase and heterogeneous surface reactions. The population balance equation governing the oxide size distribution is solved with the aid of a tailored adaptive grid method. An alternative, potentially more economical solution approach we propose is based on an embedded reduced order representation of the particle size distribution that is informed by a training step. The accuracy and convergence properties of this method are investigated for a simplified test case involving particle growth and dispersion in a laminar plane jet. In the final part of the seminar, the physical description, from an Eulerian viewpoint, of metal powders is discussed with a particular emphasis on the ramifications of carrier flow turbulence. In order to account for the small-scale interactions between dispersed particles and the ambient gas phase, the population balance equation governing the metal powder or oxide smoke is integrated into a probabilistic description that naturally accounts for the variability among independent realizations of a turbulent, particle-laden flow. Owing to the high dimensionality of the resulting transport equations, a stochastic solution approach based on Eulerian stochastic fields is proposed for which we show preliminary accuracy and convergence analyses.

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The extraction and processing of resources are directly linked to 50% of all human-induced climate impacts and 90% of biodiversity losses (Bruno Oberle et al., 2019). Promoting resource efficiency is therefore recognised worldwide as a solution approach to counteract this rapid development. The circular economy (CE) approach brings new dynamism to the discussion of the well-known concept of resource efficiency (van Ewijk, 2018; Weizsäcker et al., 1997). Both approaches aim to reduce resource use and thus prevent tremendous environmental impacts. For example, the CE is thought to be crucial for reaching climate neutrality by 2050 as well as decoupling of economic growth and resource use (European Commission, 2020). Studies estimate that eco-design, waste prevention and reuse may result in up to EUR 600 billions of savings for businesses in Europe (Kalmykova et al., 2018). The metal industry is of high importance in this discussion as metal production is responsible for 8% of the global energy expenditure (UNEP 2013). Steel production alone is responsible for a quarter of all industrial GHG emissions (Allwood et al., 2011; Ito et al., 2020). However, the metal industry and especially the steel industry can look back on a long history of recycling as a core principle of the CE resulting in great resource savings. Nevertheless, there are major doubts as to whether future steel production can be covered entirely by secondary material. This is due to the dependency of the recycling infrastructure on primary metallurgy, the limits of recycling and the low degree of circularity of steel (Haas et al., 2015; Pauliuk, Wang, et al., 2013; Steger et al., 2018; Xylia et al., 2018). In the presentation, the challenges of resource use in general as well as the possible strategies of the Circular Economy are presented and their applicability for the field of metals, in particular steel, is discussed. To illustrate this, project examples will be presented in which, on the one hand, the CE strategies of re-purposing/re-manufacturing and, on the other hand, a technical approach of sorting by specific type for recyling will be illustrated. [more]