Case Studies: Fuch's Finger Shaft EAF Installed

Finger Shaft Furnace: Maximum Productivity at Lowest Costs
The Finger Shaft Furnace technology is a development of FUCHS Systemtechnik, an affiliated company of VA Industries, in the area of electric steel making.

The Finger Shaft Furnace process distinguishes itself by maximum productivity and minimum off-gas heat loss while simultaneously reducing emissions of the steel making process. The latent and chemical heat of the off-gas is used to its maximum potential to preheat the scrap prior to melting in the EAF vessel. Thus total energy consumption can be significantly reduced. At Stahl Gerlafingen/Germany the energy consumption was reduced by approximately 100 kWh per ton while productivity increased from 104 to 120 tons per hour.

The centerpiece of a recent off-shore installation is a 95 AC Finger Shaft furnace supplied by FUCHS.

The fingers in one Furnace Shaft are used to preheat the scrap component of the charge. With the fingers in the closed position, the scrap for the next heat is suspended within the furnace shaft and is heated by the off-gas evolved during the current heat. The fingers are fully water-cooled and supported by special shock absorbers.

Oxygen and carbon are injected into the steel bath using a water-cooled lance positioned outside the furnace. This promotes the formation of a foamy slag to minimize radiation losses, protect the side-wall panels and increase thermal input efficiency. Carbon is also injected into the bath using a submerged tuyere. This additionally supports the melting of the DRI that is continuously charged into the furnace.

Natural gas is injected simultaneously through the outer ring of the tuyere and cracks as it enters the steel bath. The resultant cooling effect freezes the steel surrounding the tuyere, the so-called mushroom effect, forming a protective layer that shields the tuyere and refractory lining. By this means, it is possible to limit tuyere wear to below 0.5 mm per heat.

Six oxygen / gas jet burners (each 3 MW) are used for a period of about 5-10 minutes at the start of operations to accelerate the melting process. Two other burners (each 4.5 MW) in the vessel hood ensure that volatile organic components in the off-gas are completely combusted.

Finger Shaft technology was first introduced at HYLSA in 1994 where more than 50% of the metallic charge consists of DRI. Since then 30 additional Finger Shaft Furnaces have been sold worldwide which are charged not only with scrap but also with hot metal.

The outstanding results achieved this far in existing Finger Shaft Furnaces, such as at Stahl Gerlafingen (Switzerland) and NatSteel (Singapore), underline the furnace's advanced design criteria, high operational performance, high plant availability, low consumption figures, environmental compatibility, and the lowest conversion costs in electric steel making. More than 35 heats per day are regularly achieved, which is close to converter steel making practice.