Working Toward A Carbon-Free Steel
Steel is one of the world’s most energy-intensive industries, contributing up to 11% of global CO2 emissions. The ubiquitous material is present in nearly every building, and construction represents more than half of global steel demand. When we think of steel in buildings, we tend to conjure framing; however, most steel is used for elements other than the primary structure. According to the World Steel Association, reinforcing bars account for 44% of steel in buildings, followed by sheet products at 31%, and structural sections at 25%. Because steel is pervasive, has such a significant emissions impact, and continues to grow in demand—global crude steel production saw an increase of 11.6% last year—any serious effort to decarbonize buildings must include measurable progress to reduce steel’s carbon footprint.
Thankfully, such efforts are underway. According to a 2020 McKinsey study, four factors are driving improvements in steel’s environmental performance: the 2015 Paris Agreement, tightened carbon emission regulations, increased investor demand, and growing market support for climate-friendly steel products. Based on an analysis of 20 global steel producers, the report estimates that approximately 14% of the global steel industry’s potential value is tied to the ability to reduce its environmental impact. This value ranges between 2% and 30% for individual steel producers, making it unsurprising that the steel industry is taking decarbonization seriously, for both economic and environmental reasons.
Most steel manufacturers employ blast furnace (BF) technology to convert iron ore, coke, and limestone into crude iron and carbon dioxide. The iron is further processed in a basic oxygen furnace (BOF), producing low-carbon steel with an additional release of CO2. The energy-intensive nature of BF-BOF steelmaking leads to high carbon emissions, on the order of 1.73 tons of CO2 per ton of resulting steel. Although attaining net-zero carbon with the BF-BOF process is challenging, incremental improvements are possible. One approach involves altering the blast furnace mixture by reducing the amount of coal used to make coke and increasing the amount of iron ore. Another method deploys gas from coke ovens to offset some of the primary energy for the blast furnace. According to Resources, the most effective way to reduce CO2 emissions in BF-BOF steelmaking is to employ a carbon capture, utilization, and storage process. For example, Tata Steel in the Netherlands is developing a way to sequester the CO2 emitted from steel production in depleted natural gas fields under the North Sea. The company predicts that this method will reduce 40% of its carbon emissions by 2030.
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