Electromagnetic forces give today’s metals the sustainable edge

The electromagnetic stirrer first swirled the metallurgical melt in an electric arc furnace some 85 years ago. Since its invention at ABB (then known as ASEA) by Dr Ludwig Dreyfus, the electromagnetic stirrer, or EMS, has seen continuous development to complement evolving furnace types.

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Now it is set to play a significant role in the energy efficiency of one of the most carbon-intensive industries on the planet, enabling production of new high grade metals, including green steel, that are critical to manufacturing, the construction sector, and global economic development.

ABB Tenova innovative electric arc furnance (EAF) charging melting and electromagnetic stirring solution at Acciaieria Arvedi in Italy.

This stirrer is not a spoon. Dreyfus’s genius was to extend Faraday’s Law of induction (that a current can be induced to flow due to a changing magnetic field) to liquid metal. Patented in 1937, the significance of this invention, says Hongliang Yang, R&D Team Leader at ABB Metallurgy, was that it created an efficient, non-contact means of stirring the melt from outside the crucible, enabling both the direction and the amplitude of the stirring force to be controlled.

Positioned beside or beneath the furnace, the EMS creates a travelling magnetic field that moves the melt, resulting in more consistent temperatures throughout the molten metal, and accelerating slag-metal reactions.

In the 1930s, this represented a revolutionary step up from mechanical stirring with a rotator, which Yang says was an inefficient way of moving the melt, and also “resulted in maintenance problems” with attendant downtime.
The third known method of metallurgical stirring, blowing gases such as nitrogen, oxygen or argon into the molten mass, was not well developed at the time, says Yang. “The point where you blow gas into liquid metal can create a weak point in the furnace and there were a lot of safety issues with this technology,” he explains.

Many of these issues have since been overcome, and for some ladle furnace applications, ABB now uses electromagnetic stirrers in combination with blowing gas into the melt. “Gas stirring is particularly effective for creating the turbulent steel/slag interface that promotes desulphurization of the melt,” says Wang. ABB EMGAS, as the combined stirring technology is called, was first trialled in the early 2000s, and was found to improve performance in various steps of the ladle furnace process.

ArcSave® customize stirring force to specific process needs. The technology optimize metallurgical performance for electric arc furnace (EAF) operation.

Prior to the first commercial application of EMS technology in an electric arc furnace (EAF) in Sweden in 1947, ABB was the technological leader in manufacture of furnaces for the metals industry. “Dreyfus’s invention of the electromagnetic stirrer, which allowed him to calculate and control the current inside the liquid metal, made ABB absolutely the leading supplier of metallurgical technology in the world,” says Yang.

Since then, several thousand EMSs based on Dreyfus’s invention have been installed in metal processing applications such as EAFs, ladle furnaces (also first developed by ABB), the continuous casting of steel and aluminum remelting.

Customer interaction fuels innovation

By working closely with customers on every commissioning of its EMS products, ABB has amassed unparalleled understanding of how the technology behaves under various conditions and using different feedstock. This depth of data informs each new installation and development.

“We have the longest experience in this space in the world,” says Yang. “We have collated results from different applications of our technology, and for each customer we can provide simulations on how it will work for them.

“For almost every installation,” he continues, “we send our people to the customer site, to follow up after the installation, and to find out, ‘What are the results?’ That is I think quite special — unique in this business.”

In addition to individual customer collaborations, ABB has over decades also combined forces with major manufacturers and industry players.

In the 1980s, for example, ABB partnered with Japan’s Kawasaki Steel to apply an electromagnetic field to conventional slab casting, to further improve slab quality. The product resulting from this joint work became known as EMBR, or ElectroMagnetic BRake for the control it enabled over the momentum caused by jet flows in the slab casting process. The partnership would go on in the 1990s to develop a Flow Control Mold for conventional slab casters.

ABB electromagnetic brake solution, invented by ABB in 1985, enables steelmakers to achieve steel cleanliness similar to conventional vertical bending casters.

ABB subsequently developed a third-generation flow-control mold (FC Mold G3) to meet new market demands. And in 2016 it launched Optimold Monitor, a product that enabled temperature measurement in continuous casting, providing unparalleled process insight. Combined with the even newer Optimold Control it enables real-time, closed loop process control that takes the quality of produced metals to the next level.

Stirring up efficiencies for new arc furnaces

Partnering is vital to ongoing development of metallurgical processes, says Yang. Because parts of the processes take place at such high temperatures — 1,500 degrees Celsius or more — “you cannot imagine everything that is going on at that temperature.” He says, “You are unaware of a lot of phenomena that are occurring, or of their physical parameters, so a lot of the technology is developed on the basis of experience”. ABB’s database enables a high order of accuracy in its simulations, but still, “every new invention has to be installed somewhere to be proved before you can go further,” says Yang.

Today, steel, aluminum and other metals manufacturers are under multiple pressures: to increase the quality of their products, and reduce the carbon emitted during production, while maintaining competitive pricing. ABB’s electromagnetic stirrers have been developed for a wide variety of furnaces and processes, to increase the energy efficiency and output of metal production and give manufacturers control over their processes which in turn facilitates production of new and stronger alloys.

The greening of steel

The latest electric arc furnaces, for example, show great promise for producing significant volumes of so-called “green steel”. Powered by electricity, they can be run on energy from renewable generation; and traditionally, they have transformed scrap metals into new steel products, taking advantage of steel’s recyclability and lighting the way towards a circular economy for this essential material.

ABB Ability™ Optimold Monitor enables real-time visualization of mold temperature in continuous casting.

In 2022, ABB’s long collaboration with EAF furnace manufacturer Tenova achieved the milestone of final acceptance from steelmaker Acciaieria Arvedi for a record-breaking melting unit with a furnace tapping size of 300 metric tons.

Tenova’s Consteel EAF required an innovative adaptation of ABB’s ArcSave electromagnetic stirring technology, the latest generation of EAF-EMS,  to complement its continuous scrap charging system. “We worked together to develop a new concept of how to configure the stirrer for their particular furnace,” says Yang.

The jointly designed product is known as the Consteerrer, which has resulted in a 3.6% reduction in electrical energy consumption  (which translates into a 38,000-tonne annual reduction in the plant’s CO2 emissions) at Acciaieria Arvedi; and a 5% productivity increase, alongside a 17% reduction in final oxygen content of the produced steel. Other benefits include increased yield from scrap metals and reduced carry-over slag.

True green steel is produced using direct-reduced iron, which is formed by applying green hydrogen or biogas to draw oxygen out of iron ore, where this process was previously achieved using coke (high-carbon coal). Among ABB Metallurgy’s current R&D projects, says Yang: “We are developing EMS processes that enable us to work efficiently with this new raw material for the arc furnace.”

You can’t change what you can’t measure

Yang points out that ABB works not only on its metals technology, but on the metallurgical processes to which its products can be applied.

Another focus for his R&D team of seven researchers is digitalization: more specifically, enabling measurement using novel sensing equipment, the transfer of data to a central point and the meaningful interrogation of that data. “As I mentioned, aspects of metallurgical processes are unpredictable,” says Yang, “so measurement is very important. One of our projects involves using optical fibers to measure temperature”. Characteristics such as compact size, flexible structure, high sensitivity and immunity to electromagnetic interference make fiber-optic sensors a great fit for the metallurgical environment.

“This is a new area,” says Yang, “that will allow us to collect data, analyze it and use our findings to either control our equipment or to get new ideas to make new products.”

Yang happily admits that he is addicted to the thrill of the new, and the potential to utilize as yet unknown interactions in the crucibles of metallurgy to drive innovation and improve the sustainability of the industry — that’s one stirring mission of ongoing opportunity.

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