Causing a stir: innovations in electric steelmaking

ABB’s Senior Metallurgist Lidong Teng and Global Sales Manager Zaeim Mehraban discuss the company’s contribution to a record-breaking project with industry supplier Tenova at manufacturer Acciaieria Arvedi’s steel factory in Italy, home to the world’s highest-yielding electric arc furnace.

This article was first published in the November/December 2023 issue of Iron and Steel Today.

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The Arvedi project combines a Tenova Consteel EAF with Consteerrer, an application of ABB’s electromagnetic stirrer for optimization of flat bath EAF operations
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.

A record-breaking collaboration in Italy

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. 

ArcSave electromagnetic stirring rapidly homogenizes EAF melt temperature and chemical content

Regulating the temperature of the furnace bath

A key challenge of the Italy project was homogenizing the bath temperature. Generally speaking, the larger the furnace, the higher the temperature difference throughout the melt, so for an EAF with a tapping capacity of 300 tons, this was a significant issue. Without an EMS, there would have been an asymmetry between the hot surface of the furnace and the cold area, and the deeper the bath (at the Acciaieria Arvedi project, the bath was 1.73m deep, whereas most EAFs have a depth of 0.9-1.1m) the higher the temperature difference.

In EAF, this temperature disparity can cause the slag area to become overheated and increase refractory wearing in the slag line. However, by incorporating an EMS this heat is quickly transferred to the bottom of the melt, improving heat transfer and avoiding refractory wearing. The improved heat transfer from the arc to the melt results in a higher melt rate, shorter tap-to-tap time and less energy consumption. In addition, by stirring the melt, the slag-metal reaction is pushed closer to equilibrium, increasing the iron yield. 

The homogenizing effect the EMS has on the entire melt bath enables accurate and consistent control of temperature and overall tapping conditions. There is also evidence that this has a positive metallurgical effect during the next stage of production in the ladle furnace by, for example, lowering the oxygen content in the tapped steel.

Consteel® EAF and EMS: an innovative solution

Let’s move on to the remaining primary components of the technology package developed by ABB and Tenova for flat bath applications: the Consteel EAF and EMS.

The EMS is integrated into the bottom shell of the Consteel EAF. Unlike a traditional ArcSave EMS, the unit features coils that are installed transversal (90 degrees) to the furnace axis i.e., towards the scrap charging area.

In Tenova’s Consteel EAF the charge materials are heated by the off-gases and continuously fed into the furnace without the need for buckets or opening/shutting the furnace door or roof. The charge material is melted by immersion in the liquid steel in the furnace, resulting in high productivity, and less power costs.

Unlike other batch processes where scrap is melted by the direct action of the electric arc, Consteel works in constant flat bath conditions, with the gases from the EAF sent to a fume-cleaning plant in conditions that are suitable for complete combustion of carbon monoxide and other pollutants without any fuel usage.

Tenova’s Consteel EAF improves efficiency and safety by continuously charging the scrap into the furnace

Vital statistics: the Acciaieria Arvedi project

Deployed together at Acciaieria Arvedi’s plant in Italy, the technology developed by ABB and Tenova has resulted in increased efficiency through higher iron yield, increased furnace productivity, reduced consumption of electrodes, alloys, lime and other process additives. In addition, maintenance and manpower costs are significantly lowered. In terms of reduced environmental impact, the EMS has significantly reduced energy consumption in the furnace, while enhanced process control encompasses automated scrap quantity and quality tracking, as well as adjustable and automated stirring tailored to project needs.

In addition to the safety benefits outlined earlier, the ABB/Tenova solution also equates to reduced manpower and manual intervention on the shop floor, a significant benefit in any industrial setting.

In summary, EMS has reduced tapping temperature by 18 degrees Celsius and delivered a 3.6% drop in electrical energy consumption, resulting in an annual reduction in overall plant CO₂ emissions of 38,000-tonnes. EAF productivity has increased by 5% and final oxygen content in the EAF steel has decreased by 17%.  This is in addition to the other advantages cited earlier, which include increased scrap yield, reduced electrode use, lowered refractory wearing and less carry-over slag, while processing is more stable and final tapping conditions more easily controlled.

Accelerating sustainable steel production

The collaborative project between ABB, Tenova and Acciaieria Arvedi is a compelling example of how advancements in EAF and EMS technologies are helping steelmakers maintain productivity, safety and quality control, while simultaneously boosting energy efficiency and reducing their carbon footprint.

Lower energy consumption results in lower CO₂ emissions, while lower consumption of refractory materials, electrodes and additives also helps to reduce steelmaking’s impact on the environment.

As EMS technology gains more traction and becomes a more mainstream solution – in tandem with larger EAFs becoming the solution of choice compared with blast furnaces – so the drive towards sustainable steelmaking and net-zero emissions will accelerate, to the benefit of the industry and wider society. 

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