Researchers at the University of Michigan have mapped the annual flow of steel in the US, with the goal of achieving a detailed understanding of the flow to target increased material efficiency and the development of the circular economy.

The results of the material flow analysis (MFA), published in the ACS journal Environmental Science & Technology, indicate that yield improvement efforts should focus on sheet metal forming in the car industry, which accounts for nearly half of all generated fabrication scrap.

Formally reconciled U.S. flow of iron and steel (including embedded alloying elements) in 2014. Drawn using e!Sankey software. The iron ore flow represents the iron embedded within the ore and excludes the mass of oxygen and gangue. Credit: ACS, Zhu et al.

The research team found that the quantity of end-of-life scrap exported and land-filled is greater than the quantity of steel products imported. They suggested that increased domestic recycling of end-of-life scrap might displace around a third of imports.

The steel industry accounts for 30% of global industrial greenhouse gas emissions (GHG). The Intergovernmental Panel on Climate Change (IPCC) recommends an overall 40% to 70% reduction in GHG emissions from 2010 levels by 2050. However, with current best steelmaking practices already approaching thermodynamic limits, even deployment of cutting-edge production technologies will not be enough for the steel industry to meet the IPCC’s emissions targets.

The realization that steel production must decrease if emissions targets are to be achieved has helped lead to new research areas under the banners of ‘material efficiency’ and the ‘circular economy’, both aimed at reducing emissions-intensive material production. Researchers in these new areas require a detailed material map in order to identify opportunities.

Unlike in the developing world, U.S. per capita steel stocks plateaued around 1980. The stock saturation level has been estimated at 9.1-14.3 t/capita. Per capita stocks are expected to saturate in much of the developing world to a level similar to those in the U.S. by the late 21^st century. Therefore, the derived U.S. consumption pattern may represent a population-scaled surrogate model of the future global state.

—Zhu et al.

The researchers combined data from trade organizations, governmental scientific agencies and academic literature with monetary trade statistics and their own bottom-up estimates.

They modeled the steel flow is modeled as a series of connected nodes representing major steel processing technologies (e.g., the blast furnace) and major products used and created by industry (e.g., iron ore or passenger cars).

They used a weighting methodology to assign confidence scores consistently to the data; optimization was used to achieve mass balance and minimize the sum of the squares of the weighted residuals.

Resources

• Yongxian Zhu, Kyle Syndergaard, and Daniel R. Cooper (2019) “Mapping the Annual Flow of Steel in the United States” Environmental Science & Technology doi: 10.1021/acs.est.9b01016