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The figure shown below schematically describes the Mitsubishi Process,
illustrating its sequence of continuous and controlled smelting of copper
concentrates, coal, and flux; the separation of copper matte and discard
slag; the continuous conversion of copper matte to blister copper; and
finally, the continuous delivery of blister copper to the anode furnaces.
Three launder-connected furnaces are used: a circular smelting(S) furnace,
an elliptical slag cleaning(CL) furnace, and a circular converting(C) furnace.
The mixture of matte and slag formed in the S furnace flows continuously
to the CL furnace, where the denser copper matte separates from the discard
slag. The matte is then siphoned to the C furnace, to be continuously converted
to blister copper and C-slag. The latter is water granulated, dried, and
recycled to the S furnace, while blister copper is siphoned continuously
from the C furnace to the anode furnaces.
A number of lances are used to inject the
S furnace feed materials and oxygen-enriched
air, straight down to the melt surface. The
slowly consumed lances have their tips regularly
adjusted to around 700mm above the melt surface.
Pneumatically controlled hoppers pulse-feed
the solids to the top of each lance. High
air-oxygen blowing rate ensures that the
gas/solids mixture leaving each lance tip
has an average linear velocity of about 200
m/s.
Because the number of lances operated can be easily changed during operation,
the flexibility for the change of concentrate composition and feed rate is much
larger than the other processes.
In the melt below the lances, transient cavities, or "jet holes",
continuously form and collapse, creating a turbulent, high-intensity reaction
zone, in which virtually all of the feed particulates are captured and
melted. Dust carry-over into the gas cooling and cleaning equipment is
minimal. The C furnace uses a similar multi-lance system to inject flux,
oxygen-enriched air, and coolant down into the high intensity reaction
zone in the melt.
Although the melt just beneath the lances is intensely agitated, there is only small
waving on the melt surface near the side wall, and this waving motion has no relation
with the number of lances operated. Accordingly, high efficient reaction and friendliness
to the refractory are well balanced.
Materials with a fairly high silica content are used as the primary flux
for the S furnace. Limestone, however, is the chosen flux for the C furnace,
since a more fluid ternary slag of the Cu2O-CaO-Fe3O4 type is desired.
This copper-containing C slag is water granulated, dried, and recycled
to the S furnace.
The SO2 rich off-gases from the S and C furnaces are drawn via respective
furnace uptakes into waste heat boilers and electrostatic precipitators
where they are cooled and cleaned before delivery to the acid plant.
During normal operations, no fuel oil is burned in either the S or the
C furnace.
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