• A global emission inventory of global iron and steel plants has been prepared that contains nearly 29,999 individual processing units located in nearly 4,900 individual iron and steel plants. 
• The main production technology used by the global steel industry is the basic oxygen furnace. Approximately 28% of production involves the use of electric arc furnaces that generate lower levels of carbon dioxide emissions.
• By implementing a carbon dioxide mitigation pathway for each plant, the researchers estimated that global carbon dioxide emissions could decline by 58.7 gigatons between 2020 and 2050, which is equivalent to two years of net global carbon dioxide emissions.

In the quest for sustainability, emissions reduction is a critical factor. As noted in the 2023 STLE Report on Emerging Issues and Trends in Tribology and Lubrication Engineering,¹ iron and steel production generates a significant quantity of carbon dioxide emissions. Global production of 1.9 billion metric tons of steel led to the generation of 2.6 billion metric tons of carbon steel according to the World Steel Association. This emissions figure accounts for 7%-9% of global anthropogenic carbon dioxide emissions. 

One of the leading manufacturing processes for producing steel is the basic oxygen furnace where pig iron is passed through a basic oxygen furnace to remove carbon in the form of carbon dioxide and produce crude steel. This process along with the manufacture of coke needed to produce pig iron represents a large share of carbon dioxide emissions. 

Dabo Guan, professor in climate change economics and the low carbon transition at University College London in London, UK, says, “Approximately 72% of the world’s steel production can be attributed to the use of a blast oxygen furnace.” 

Guan’s interest in studying carbon dioxide emissions originated in China. He says, “We started by compiling carbon dioxide emissions in 300 Chinese cities. This led to the development of emissions data and work in determining the source of the emissions.” Initially, Guan and his colleagues evaluated emissions from over 14,000 power generation plants in China. The next objective was to focus on other highly emitting sources such as steel and iron manufacturing facilities on a global basis. He says, “We conducted a project to estimate carbon dioxide emissions originating from the iron and steel industry on a plant-by-plant basis.” 

Data generated from this work was then used to estimate how the global iron and steel industry can upgrade individual plants to reduce carbon dioxide emission.  



Carbon dioxide emissions inventory 
The researchers developed a global emissions inventory for global iron and steel plants that is based on nearly 20,000 individual processing units located in nearly 4,900 individual iron and steel plants. Guan says, “We defined a processing unit as a facility conducting a specific operation in the steel making process such as coking sintering, ironmaking, steelmaking, etc. There are 17 different types of processing units in facilities located in the main geographical regions doing steel making which are China, Europe and the U.S.” 

The researchers used 2019 as the base year for their study. Guan says, “We used 2019 as this was the most recent year that we could obtain data which was representative of normal steel production prior to the COVID-19 pandemic.” 

Based on their analysis, the researchers determined that total global crude steel capacity is just under 2,600 megatons. While much of the steel industry is using basic oxygen furnaces, about 28% of production involves the use of electric arc furnaces that generate lower levels of carbon dioxide emissions. 

Identifying the many individual iron and steel plants operating globally would seem to be a major challenge for the researchers. Guan says, “We developed data through an extensive literature search where many steel manufacturers list their production capacity in documents such as annual reports. Further information was obtained from company websites.” 

Iron and steel plants were organized into six categories based on the number of years of operation (0-4, 5-9, 10-14, 15-19, 20-24 and greater than 25). Guan says, “We found that about 50% of crude steel output accounted for over 50% of total emissions. A main reason for this is that many of these plants are equipped with coal-based processing routes. This conclusion was made because we know the basic plant types used in steel processing.” 

The researchers then developed a series of carbon dioxide mitigation pathways to be tailored to each individual steel plant. Guan says, “We analyzed how each plant could improve its process efficiency, change from burning fossil fuels to using electricity and determine whether the electricity can originate from a renewable source.” 

To effect this change, the researchers projected carbon dioxide emissions based on when individual plants will be able to retrofit to use more renewable processing. Guan says, “We estimated carbon dioxide emissions based on plants undergoing retrofitting during their planned year, doing the processes five years earlier, and five years later. The most benefit was found when plants upgraded their facilities at the early benchmark.” 

Guan acknowledges that having steel plants retrofitted prior to their designated timeline is challenging. He says, “Retrofitting occurs over different timeframes in specific regions. For example, China’s steel plants go through retrofitting every 14 years while in the U.S., plants upgrade after 20 years. The decision for retrofitting is usually made by the plant manager.” 

In projecting retrofitting of steel plants globally, the researchers calculated that global carbon dioxide emissions could decline by 58.7 gigatons between 2020 and 2050 which is equivalent to two years of net global carbon dioxide emissions. If all retrofitting is completed five years earlier than scheduled, emission savings might increase to as much as 69.6 gigatons. 

Guan says, “Our analysis did not factor in confidential information about production facilities, the type of steel produced which can impact emissions due to additional processing steps and not knowing the sources of emissions.” 

The work conducted by Guan and his colleagues illustrates the potential for reduction of emissions if the global steel industry can upgrade its facilities. Guan says, “We will be evaluating future decarbonization pathways for individual plants and assessing the economic cost of doing the retrofitting.” 

Additional information on this research can be found in a recent article² or by contacting Guan at d.guan@ucl.ac.uk. 

REFERENCES
1. 2023 STLE Report on Emerging Issues and Trends in Tribology and Lubrication Engineering. Available at www.stle.org/2023EmergingTrendsReport. 
2. Lel, T., Wang, D., Yu, X., Ma, S., Zhao, W., Cui, C., Meng, J., Tao, S. and Guan, D. (2023), “Global iron and steel plant CO₂ emissions and carbon-neutrality pathways,” Nature, 622, pp. 514-520.