Electric dreams: advancements in arc furnaces and electromagnetic stirring

Innovations in electric steelmaking, specifically arc furnaces and electromagnetic stirring, can help manufacturers boost efficiency, productivity, process control and sustainability. Zaeim Mehraban, Global Sales Manager and Lidong Teng, Senior Metallurgist, at ABB’s Metallurgy team, explain how.

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The ABB-Tenova technology solution deployed at Arvedi, Italy, enables continuous charging and more efficient melting of scrap

Industrial steelmaking is undergoing perhaps the most profound transformation in its long history. 

Driven by Industry 4.0 and the urgent need to reduce greenhouse gas emissions in line with treaties such as The Paris Agreement on climate change, steelmaking is evolving from an energy and CO2-intensive industry that deploys blast furnace-basic oxygen furnaces (BF-BOF) fuelled by coal and iron ore, to one that uses electric arc furnaces (EAFs) to produce steel mostly from scrap.

The industry is responsible for around 7% of global CO2 emissions, and the onus is on manufacturers to replace fossil fuel-based carbon with green hydrogen to produce steel more sustainably using renewable energy, while at the same time maximising production to satisfy growing demand as well as reducing raw material costs.

Steelmaking must become increasingly smart if it is to ride out the current storms to a more sustainable future. EAFs coupled with electromagnetic stirring (EMS) – whereby an electromagnetic force stirs the entire steel melt, the direction, duration and intensity of which are adjustable – is one way of making that change to a smarter future.

In this article, we will look at innovations in electric steelmaking, specifically process improvements after installation of a leading-edge charging, melting and EMS solution that would become the world’s most productive electric arc furnace. Operated by Acciaieria Arvedi, this record-breaking furnace features a tapping size of 300 metric tons, and results show increases in arc heating efficiency, scrap melting rate and scrap yield, and reduced electrical energy consumption, power-on time and oxygen content in the steel.

EAFs: characteristics, advantages and limitations

Unlike traditional BF-BOF furnaces in integrated steel plants, which produce steel using virgin iron ore, more factories – greenfield facilities in particular - are increasingly choosing to make the direct reduced iron (DRI) and/or hot briquetted iron (HBI) by hydrogen reduction process and then melting them in the EAF.

As we have mentioned, EAFs offer obvious sustainability advantages over blast furnace production, especially if low-carbon forms of electricity continue to become more widely available. An increase in the availability of scrap steel, as much as a billion metric tons by 2030 will support the growth in EAF production. The recycling of steel is an ‘easy win’ for the circular economy in that it simultaneously reduces the overall CO2 footprint of steel production and the need for newly mined raw materials.

In an EAF, the EMS hardware is installed under the furnace, but, importantly, not in contact with the melt, and creates a travelling electromagnetic field that penetrates the furnace, producing a magnetic force within the melt that produces the stirring effect. The contactless installation not only results in improved mass and heat transfer through the melt, it also avoids the risk of breakthrough and extensive maintenance that comes with employing gas purging plugs for bottom gas stirring (BGS).

However, there are disadvantages to EAFs. There can be an asymmetry between the cold area of the furnace where the steel scraps are charged and the hot area. The EAF process’s inefficient melting of scrap and alloys reduces productivity, energy efficiency and yield, and can cause bottom skulls, a particular challenge for stainless and special steel producers that reduces furnace capacity. Also, predicting final tapping conditions is challenging due to varying thermal and chemical conditions.

To address these issues, and others, ABB developed ArcSave® electromagnetic stirring technology, which creates a global stirring effect, without dead zones or cold spots, and much higher stirring power when used with an EAF, improving productivity and yield while lowering operating costs.

Technology can help bridge the productivity gap facing steelmakers moving form BF-BOF to more sustainable EAF steelmaking

ABB ArcSave®: efficiency, productivity, control, safety

Before focusing in more depth on the collaborative project involving ABB, Tenova and Acciaieria Arvedi, let’s briefly look at one of the two key technologies involved, the ArcSave EMS solution.

ABB’s ArcSave enables safer, more consistent and efficient arc furnace operations. To take the latter first; when we talk about efficiency in the EAF process we primarily mean energy. The steel furnace process is extremely energy-intensive, meaning even a small saving equates to big absolute numbers in terms of reduced energy consumption and CO2 emissions. During the Acciaieria Arvedi project, the application of EMS resulted in a 3.6% reduction in electrical energy consumption. Efficiency also refers to raw materials, specifically the yield of the iron scrap used in the EAF to produce steel.

Blast furnaces have an extremely high rate of productivity; to constitute a realistic alternative, EAF solutions must match, or even exceed, this output if steelmakers are to hit their sustainability goals while remaining cost competitive. During the Italy project, EMS increased productivity by 5%.

Another benefit of EMS systems in general, and ArcSave in particular, is improving process control in terms of the stability and repeatability of the process, and much more accurate furnace temperature readings and homogenisation; in other words, when you measure the temperature in one place in the EAF, you can be more confident that this is the same temperature over the entire bath.

Finally, there is the issue of safety. In the EAF context, this means the opening of the EBT (eccentric bottom tapping) to tap the steel, a potentially dangerous process if the hole cannot be opened properly due to unmelted frozen scrap. EMS reduces this risk by improving scrap melting and ensuring a high EBT free opening ratio. Secondly, alternatives to EMS use inert gases like argon to stir the melt by purging them through porous plugs or holes in the bottom of the furnace, increasing the risk of a breakout of molten steel. EMS solutions remove the need for such holes as weak points. 

In summary, ABB ArcSave EMS offers efficient heat transfer from the arc to the melt; a higher melt rate, shorter tap-to-tap time and lower energy use; and pushes the slag/metal reaction closer to equilibrium, increasing yield, and also efficiency, productivity and sustainability for manufacturers.

Case study: ABB, Tenova and Acciaieria Arvedi

At steel manufacturer Acciaieria Arvedi’s site in Italy, ABB has partnered with technology provider Tenova to deliver a powerful solution that enables optimal charging and melting for the world’s highest-yielding EAF, which has a furnace tapping size of 300 metric tons.

The package combines a Tenova Consteel® EAF continuous scrap charging system with a model of the ABB ArcSave EMS system designed specifically for continuous charging EAF systems, which Tenova often refers to as Consteerrer®.

In Tenova’s Consteel EAF, the raw feed materials are pre-heated and charged continuously (avoiding the need for buckets or to open the furnace door or roof during the process) and melted by immersion in the liquid steel present in the furnace, while simultaneously controlling gaseous emissions. The results are liquid steel with high productivity, a short and adjustable heat cycle and low power costs.

The charge is loaded, from a scrap yard, onto the charge conveyor and pre-heated by process off-gas as it is continuously fed into the EAF. The furnace operates in constant flat bath conditions, a key advantage over other batch processes where scrap is melted by the direct action of the electric arc. The EAF gases are sent to a fume-cleaning plant in conditions suitable for complete combustion of carbon monoxide and other pollutants without any fuel usage.

This particular EMS model was jointly developed by ABB and Tenova and is integrated into the bottom shell of the EAF. The EMS has delivered a range of process improvements at Acciaieria Arvedi. These include an 18 degrees Celsius lower tapping temperature and a 3.6% drop in electrical energy consumption, resulting in a 38,000-metric ton annual reduction in overall CO₂ emissions at the plant. EAF productivity has increased by 5% and final oxygen content in the EAF steel has decreased by 17%.

Other benefits include increased scrap yield, reduced electrode consumption, lowered refractory wearing and less carry-over slag. Processing is more stable and final tapping conditions more easily controlled.

In summary, the ABB/Tenova solution provided to Acciaieria Arvedi has increased efficiency (higher yield, lower carry-over slag, etc); reduced environmental impact (energy-efficient EAF); enhanced process control (no buckets, automated scrap quantity and quality tracking); and improved safety (less manpower and manual intervention in hazardous areas, etc).

Using non-contact electromagnetic stirring technology avoids the break-through risk associated with bottom gas stirring

Forward thinking

EAF-EMS brings multiple benefits to the process of EAF steelmaking enabling companies to maintain productivity while simultaneously reducing OPEX – EAF-EMS has been shown to offer much lower operating costs, in the range of 20% to 40%, than BGS – and tackle the challenge of sustainability.

Lower energy consumption results in lower CO₂ emissions, while less refractory materials, electrodes and additives also helps to reduce the overall impact of the steel industry on the environment.

There is a consensus in the market about the increased need for EMS, particularly considering that 43% of planned steelmaking capacity globally will rely on EAFs and that figure needs to rise to 53% by 2050 to achieve net zero steel production. 

Steel manufacturers that recognise this trend, and get ahead of the curve by investing meaningfully in EMS technologies, in partnership with a trusted technology provider, can not only look forward to a useful competitive advantage, but also a greatly reduced carbon footprint on the road to net zero. 

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