For steel manufacturers, the pressure is on to maintain and even exceed current production levels to meet increased global demand resulting from population and economic growth, particularly in India, ASEAN countries and in Africa. However, this must be balanced with the urgent need to reduce greenhouse gas (GHG) emissions from steel production, which is still highly reliant on coal, primarily as a reducing agent to extract iron from iron ore and to provide the carbon content required in steel.
If the industry is to reduce its carbon dioxide (CO2) footprint quickly enough to align with the goals of environmental treaties such as the Paris Agreement, technologies such as carbon capture and hydrogen-based production must be developed at scale, in tandem with efforts to optimize the efficiency of iron and steel production processes and the electrification of ancillary services.
Electric arc furnaces (EAFs) that produce steel from scrap metal or green DRI – as opposed to blast furnace-basic oxygen furnaces (BF-BOF) fueled by coal and iron ore – are a compelling example of the type of innovation that can be leveraged by steelmakers to accelerate more sustainable steel production practices.
EAFs offer distinct sustainability advantages compared with BF-BOF furnace production, driven by the wider availability of both low-carbon electricity and scrap steel. After all, recycling steel as part of the wider circular economy reduces steel’s CO2 footprint and the need for fresh raw materials.
In many integrated steel plants, conventional BF-BOF furnaces use virgin iron ore to produce steel, but more and more plants, particularly greenfield factories, are looking to make the direct reduced iron (DRI) and/or hot briquetted iron (HBI) by hydrogen reduction process and then melting them in the EAF.
In this article, we will take a look at how EAFs work in more detail, along with recent advancements in electromagnetic stirring (EMS) technology, and how a recent collaborative project involving leading metals industry suppliers ABB, Tenova as well as Italian operator Acciaieria Arvedi is pushing the boundaries of steel production using EAF and EMS, enabling companies to commit to their sustainability targets and remain cost competitive.
Acciaieria Arvedi’s plant in Italy is home to the world’s highest-yielding EAF. The record-breaking furnace has a tapping size of 300 metric tons, a charge mix that includes HBI and pig iron, and is 9.1m in diameter.
Installed to meet the demand for increased output following the revamp of the continuous Endless Strip Production (Arvedi-ESP) casting and rolling mill line at the flagship facility, the plant combines a Tenova Consteel® EAF with an application of ABB’s ArcSave® electromagnetic stirrer. The technology is jointly developed by ABB and Tenova specifically for flat bath EAF operations and is also referred to as Consteerrer®.
While EAFs offer many advantages over BF-BOF furnaces, issues persist. Inefficient melting of scrap and alloys can negatively impact productivity, energy efficiency and yield, in addition to causing bottom skulls, which reduce capacity in stainless and special steel plants. Moreover, predicting the final tapping conditions can be challenging as a result of varying thermal and chemical conditions.
ABB’s ArcSave EMS is specifically designed to address these issues, enabling safer, more consistent and efficient EAF operation. At its core is a coil conductor. The unit sits under the furnace secured by a support cradle, and is fitted to a non-magnetic stainless steel bottom or window. ArcSave works by generating a travelling electromagnetic field that penetrates the furnace, creating a magnetic force that produces the stirring effect, resulting in improved mass and heat transfer throughout the melt.
The duration, direction and intensity of the stirring can be adjusted, manually by operators, or automatically by a control system integrated into the furnace automation system. The EMS rapidly homogenizes the thermal and chemical composition, avoiding cold spots/dead zones in the melt and ensuring that the temperature remains constant over the entire bath, resulting in improved resource efficiency in the EAF. What’s more, process stability and repeatability are enhanced, and furnace temperature readings are more reliable and precise, a boon in terms of process control.
Unlike competing stirring solutions, the EMS has no contact with the furnace or the melt, which not only equates to a longer lifespan and lower maintenance costs, but also avoids the risk of breakthrough inherent to the use of the gas purging plugs for bottom gas stirring.
In terms of safety – which, encouragingly, remains an industry priority – using EMS will improve scrap melting and significantly reduce the risk of unmelted scrap blocking the opening of the EBT (eccentric bottom tapping) hole used to tap the steel. When such blockages occur, O2 lancing is used instead; a hazardous and time-consuming task that reduces process safety and productivity. Secondly, unlike competing stirring technologies, EMS does not require porous plugs (holes) in the furnace bottom shell, removing the associated risk of breakthrough.