Electromagnetic forces give today’s metals the sustainable edge

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.

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.

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 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.

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.”