In terms of steel-making technologies, CCUS is regard as the most promising technology. carbon dioxide emitted during operation is separated from other gases and captured. The captured carbon dioxide is then transported via pipeline or to onshore or offshore storage sites, or used. The CCUS process involves post-combustion/pre-combustion capture, compression, transportation, and storage/use. Figure 3 shows a CCUS scheme for a simplified blast furnace-basic oxygen furnace (BF-BOF) steelmaking route.
The main advantage is that CCUS systems can be easily integrated into existing conventional brownfield plants. Furthermore, since the technology is not specifically designed for steelmaking, other industries can share development and infrastructure costs. Additionally, future operating costs are largely predictable.
The main disadvantage is that CCUS is not completely carbon neutral, as the carbon capture process alone only captures approximately 90% of the carbon dioxide. There are also other challenges. Public acceptance of carbon storage is uncertain, putting early adopters at a disadvantage. Moreover, currently, apart from small-scale onshore storage sites, the ocean is the only suitable large-scale storage location, requiring significant transportation efforts. Furthermore, the utilization of emissions is also a process to ensure no carbon emissions in the later stages, achieving carbon neutrality. Additionally, CCUS equipment increases maintenance burden and downtime, significantly impacting operating costs.
Some pilot projects have begun treating emissions such as carbon dioxide to produce synthetic fuels. However, this is not yet carbon neutrality because carbon dioxide is emitted later.
Biomass-based Ironmaking and CCUS
The basic idea behind these technologies is that carbon-neutral biomass partially replaces fossil fuels in pretreatment or serves as a reducing agent for iron ore. Examples include using carbon-rich “coke” made from virgin biomass (virgin seaweed, grass, wood, etc.) to produce alternative coke, or injecting biogas into shaft furnaces to replace natural gas. Processes based on these technologies include pyrolysis and hydrothermal carbonization. The CCUS system handles any remaining carbon emissions.
Biomas alone can reduce carbon dioxide emissions by 40% to 60%, and when combined with CCUS, carbon-neutral steelmaking can be achieved. In the short term, biomass can immediately partially replace fossil fuels, enabling existing plants to quickly achieve emission reduction goals. Carbon dioxide emissions can also be recovered using CCUS to produce new biomass.
However, biomass cultivation is challenging. Environmentally, it can lead to deforestation, pollution, and biodiversity loss; socially, it impacts food prices and agricultural land use. Therefore, the risks to political and social acceptance are high. Furthermore, biomass has a lower calorific value than fossil fuels, limiting its use in large blast furnaces or causing reduced efficiency. Additionally, its high water content may make it too heavy for large blast furnaces.
A study conducted by the Swedish research team SWEREA at the SSAB steel plant in Lulea on the use of biomass found that using biomass in ironmaking can reduce carbon dioxide emissions by 28%.