/ Steel (Ferrous): Scrap Preheating Systems
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
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.
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.
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.
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.
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."
systems can generally provide dry preheated scrap that will reduce electrical
consumption by 50 to 80 kWh per ton.