Iron / Steel (Ferrous): Scrap Preheating Systems

Scrap preheating is used in both integrated steel mills and in mini-mills to decrease furnace melt energy costs, increase production and to provide dry (and safe) scrap prior to furnace charging.

Integrated mills utilize scrap (in some cases up to 30%) in the BOF steel making operation. Complete burner and control packages have been developed to efficiently preheat ferrous scrap using non-water-cooled oxy-fuel burners. Air Products has demonstrated that 70% fuel savings and 50% reductions in heat-up rates are typical.

Modern EAF designs will provide for closed vessels, continuous charging, scrap preheating, and post-combustion, and that scrap preheating to temperatures near and above 600°F will be commonly applied.

Though some preheating systems have been in use for more than a decade, others, such as twin-shell EAF furnaces (shown below) are more recent developments that incorporate preheating as an integral part of the melting process. At a twin-shell, while one part of the furnace is making steel, the other side is being loaded with scrap. The off-gas from the operating side of the two-furnace system is piped to the other side to heat the charge before melting.

Air Products has also supplied systems for retrofit into existing EAF operations. A paper presented at the 2002 EEF Conference illustrates the experience of 4 steel firm that recently began using the patented JetBOx™ technology (two in North America) for Oxy-fuel scrap preheating and other reasons to attain production related benefits. A table illustrating the overall benefits of using these oxy-fuel systems for one of the installations is shown below.

There are two commercially proven preheating methods: the Fuch's shaft furnace and the Consteel continuous process. The Fuch's method can use burners to combust the fumes exiting the preheat chamber. The Consteel process is a conveyor-fed, continuous scrap-delivery system. It's basically a 5-foot-wide conveyor in a closed tunnel that's preheated with the off-gas from the EAF and may, or may not, utilize an afterburner to combust CO (and therefore return additional heat to the scrap) and control emissions. One user of the Consteel process (developed in the late 1980's by Intersteel Technology Inc., later purchased by Italian supplier Techint S.p.A.) is AmeriSteel.

The main benefit of the system is the opportunity to melt continuously, says Dennie Andrew, Senior VP of Operations at AmeriSteel. AmeriSteel is installing another Consteel system as part of the melt-shop rebuild at its Knoxville, TN facility. "It lowers your operating costs, reduces the energy costs to melt scrap, and reduces the tap-to-tap time by about 10 percent," Andrew says. "We get a 400° scrap preheat. The kicker is that we never take the roof off the furnace; the scrap is charged into the side."

Scrap preheating systems can generally provide dry preheated scrap that will reduce electrical consumption by 50 to 80 kWh per ton.