Furnace Electrode for Steel-Making

         Melting I

       
The melting period is the heart of EAF operations. The EAF has evolved
into a highly efficient melting apparatus and modern designs are focused
on maximizing the melting capacity of the EAF. Melting is accomplished
by supplying energy to the furnace interior. This energy can be
electrical or chemical. Electrical energy is supplied via the graphite
electrodes and is usually the largest contributor in melting operations.
Initially, an intermediate voltage tap is selected until the electrodes
bore into the scrap. Usually, light scrap is placed on top of the
charge to accelerate bore-in. Approximately 15 % of the scrap is melted
during the initial bore-in period. After a few minutes, the electrodes
will have penetrated the scrap sufficiently so that a long arc (high
voltage) tap can be used without fear of radiation damage to the roof.
The long arc maximizes the transfer of power to the scrap and a liquid
pool of metal will form in the furnace hearth At the start of melting
the arc is erratic and unstable. Wide swings in current are observed
accompanied by rapid movement of the electrodes. As the furnace
atmosphere heats up the arc stabilizes and once the molten pool is
formed, the arc becomes quite stable and the average power input
increases.

        Melting II

        Chemical
energy is be supplied via several sources including oxy-fuel burners and
oxygen lances. oxy-fuel burners burn natural gas using oxygen or a
blend of oxygen and air. Heat is transferred to the scrap by flame
radiation and convection by the hot products of combustion. Heat is
transferred within the scrap by conduction. Large pieces of scrap take
longer to melt into the bath than smaller pieces. In some operations,
oxygen is injected via a consumable pipe lance to"cut" the scrap. The
oxygen reacts with the hot scrap and burns iron to produce intense heat
for cutting the scrap. Once a molten pool of steel is generated in the
furnace, oxygen can be lanced directly into the bath. This oxygen will
react with several components in the bath including, aluminum, silicon,
manganese, phosphorus, carbon and iron. All of these reactions are
exothermic (i.e. they generate heat) and supply additional energy to aid
in the melting of the scrap. The metallic oxides that are formed will
end up in the slag. The reaction of oxygen with carbon in the bath
produces carbon monoxide, which either burns in the furnace if there is
sufficient oxygen, and/or is exhausted through the direct evacuation
system where it is burned and conveyed to the pollution control system.
Auxiliary fuel operations are discussed in more detail in the section on
EAF operations .

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