Greenhouse Gas Mitigation Technologies for the Industrial Sector. Part I: Iron and Steel Industry

The Carbon Footprint of the Iron and Steel Industry

This is the first part of our series discussing mitigation strategies for the industrial sector. Process emissions from manufacturing industries accounted for over 28% of global emissions in 2017 [1, 2]. The iron and steel industry produces 7-10% of greenhouse gas (GHG) emissions worldwide. In perspective, this is equivalent to 1.5 times more emissions than the emissions generated from road freight or nearly three times the emissions originated by aviation. The carbon footprint of the iron and steel industry has become the focus of attention in recent decades as steel production is expected to grow at a steady pace. Despite the impact of COVID-19, the demand for steel is anticipated to grow by 2-3% per year by 2050 as a result of the increase in demand by emerging economies, in particular in South East Asia, Africa, and Latin America [1, 3].

Mitigation Technologies in the Iron and Steel Industry

Blast Furnace & Basic Oxygen Furnace (BF-BOF) and Electric Arc Furnace (EAF)

Steel production is among the more energy-intensive industries with about 1.85 tonnes CO₂eq per tonne of steel produced. More than a third of global steel manufacture is produced by conventional blast furnace (BF) and basic oxygen furnace (BOF) processes. This route requires metallurgical coke to produce pig iron in the blast furnace. Later, pig iron is processed in BOFs to eliminate excess carbon and produce raw steel. The remaining steel produced worldwide (about 30%) is made in electric arc furnaces (EAF) using sponge iron and/or scrap steel as raw materials.

Steelmaking by the BF-BOF route is known to have higher emissions intensities than the traditional EAF process (Figure 1), however, the BF-BOF process has proven to be more cost-effective at large production scales. In addition, the production of EAF steel depends strongly on the availability of scrap steel.

Emissions intensities for BF-BOF and EAF steelmaking in different counties. Data corresponds to 2016 steel production compiled by Global Efficiency Intelligence

Figure 1: Emissions intensities for BF-BOF and EAF steelmaking in different counties. Data corresponds to 2016 steel production compiled by Global Efficiency Intelligence [2].

Smelt Reduction with Hydrogen

Efforts on the decarbonization of the iron and steel industry focus, among others, on increasing the share of EAF steel in the market. One method to achieve this is the smelt reduction process, in which mineral ore is directly reduced and smelted (often in the same vessel) in the presence of oxygen. Hot metal from smelting reduction has a similar quality to pig iron from BFs and can be fed to BOFs, EAFs, or cast pig iron. Even though coal or coke can be used as reducing agents as in BFs, emerging technologies are opting to reduce the ore with natural gas or hydrogen. Less processing steps and lower energy consumption compared to BF-BOF steel translate in overall higher efficiencies and lower emissions.

Whereas BF-BOF has energy intensities of about 22-28 GJ/tonne steel, direct smelting technologies promise to reduce this to 18-20 GJ/tonne [1, 3, 7]. In addition, emissions from the production of metallurgical coke are avoided as this material is no longer needed (~3.5 GJ/tonne coke). IRENA reported that steelmaking emission intensities can be reduced to 0.09-0.38 tonnes CO₂/ tonne steel when green hydrogen is used as a reducing agent (or 80-95% emissions reduction, see green box in Figure 1). The same source estimates a marginal abatement cost for this technology at about $67 USD/tonne CO₂, however, this cost strongly depends on the availability of low-cost renewable electricity.

Coke in Blast Furnaces

Other technologies that have found their place in existing plants target the use of coal or coke in blast furnaces. For example, injection of natural gas or charcoal from biomass can reduce up to 8-15% of CO₂ from blast furnaces [3, 6, 7]. Still, the use of coke is necessary to provide structural support.

Energy Efficiency Improvements

Energy efficiency improvements such as continuous casting and rolling, energy recovery from BFs and coke oven gas, or advanced process control can help to mitigate up to 20% of emissions from steel production. Carbon capture, utilization, and storage (CCUS) can also supplement the abatement strategy by 25-40% [1, 3]. Supplemental technologies such as fuel switching for heat/power production and renewed steel recycling programs (mainly from automotive and construction) will be also key to reach net-zero emissions in this sector. Many of these technologies have already reached abatement costs under $200 USD/tonne CO₂ and are, by the most part, available for rapid implementation in existing facilities. Continuous technological improvements in this area are likely to transform steel production into a carbon-neutral industry in the next couple of decades, probably sooner.

Figure 2: Classification of GHG mitigation technologies for the iron and steel industry. Adapted from the Fact Sheet on Climate Change Mitigation.

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