German engineering company SMS Siemag has developed the Arccess steady electric arc furnace (S/EAF), which allows continuous operation for up to one week.
EAFs are the core units of an electric steelmaking plant and have a significant impact on production and energy costs.
The development of the S/EAF arose from SMS Siemag’s long-standing experience in the fields of submerged-arc furnaces (SAFs), EAFs and its Conarc technology.
The result is a new type of EAF that yields 30% higher productivity with lower energy consumption because of its reliable continuous process. The integrated energy recovery system further improves efficiency by using the thermal energy of the hot furnace offgases.
All components have been designed to allow for continuous power-on operation for about one week. Uninterrupted operating practice is made possible by a patented system derived from SAF technology, which enables the electrodes to be clamped and slipped continuously. Whenever an electrode has been used up, a fresh piece of electrode is joined at its end. Both operations take place under ‘power-on’ settings.“
Continuous operation in SAFs is only possible by the electrode slipping device.
“That this principle will now be transferred into the new S/EAF is a real innovation and it definitely results in increased efficiency,” says RWTH Aachen University Institute for Machine Elements and Machine Design professor Bernd Friedrich.
Similarly, with the operation of an SAF, the process takes place in a uniform way and is almost free of fluctuations, since the S/EAF is operated continuously in the flat bath phase.
The geometry of the new furnace shell has been improved accordingly and comprises a flat lower shell and a conical furnace roof placed closely on top.
The S/EAF is continuously charged with direct-reduced iron-ore/hot briquetted iron (DRI/HBI), hot metal or scrap through a materials handling system that is also rated for the use of 600 °C hot DRI.
In addition to the electrodes, water-cooled oxygen-blowing lances are introduced through the furnace roof. This technology has been adopted from Conarc – a furnace unit developed by SMS Siemag with the aim to rapidly decarburise melts with a high carbon content. The level of foaming slag is controlled by a new, patented slag door system. The steel is tapped slag-free and under ‘power-on’.
Since the S/EAF is not opened during operation, no roof hood for the secondary gas collection is needed. Primary gases are directly exhausted through a furnace nozzle. This allows the connected gas cleaning plant to have smaller dimensions.
The power-off times that previously affected the EAF no longer arise, states SMS Siemag.
Continuous operation is interrupted only for regular maintenance work. For that purpose, the lower furnace shell can also be driven to a maintenance stand. No heavy-duty gantry cranes, elaborate building structures or foundations are needed.
The steady input of electrical energy and the flat-bath process prevent negative feedback on the electricity grid. Further advantages are the protection of the refractory lining and lower specific electrode consumption.