1 ton / day Pilot Plant
(200 kVA DC-arc facility)
The 1 ton / day DC-arc facility consists of:
- DC-arc furnace (1.5 kA max)
- Feed system (0.2 t/h max)
- Off-gas handling plant (6 500 Nm³/h)
- Power supply 1 x 1.6 MVA transformer/rectifier
- Control and instrumentation systems
Description of the pilot plant
The furnace consists of a refractory-lined cylindrical shell and
a conical roof. The shell can be lined with refractory bricks, or with
castable or rammable refractory material, depending on the type
of refractory needed. The hearth is usually lined with ramming material.
The roof is lined with a alumina castable refractory. The furnace
is equipped with water-spray cooling on the sidewalls and with water cooling jackets on the
A graphite electrode with an outer diameter of 75 mm is used
as cathode. The electrode enters the furnace through the centre
port in the flat roof. This electrode port consists of a water-cooled,
refractory-lined electrode seal to ensure that there is no electrical
contact between the electrode and the roof. The anode consists
of several steel bars, built into the hearth refractory and connected
at their lower ends to a steel plate. The steel plate is connected
to the furnace shell and then to the anode cable.
The feed system consists of six holding bins, each connected to
a feed hopper. The hoppers vary in size and feed rate capabilities
to ensure that accurate feed rates can be attained at high and
low rates. Each of the feed hoppers rests on three load cells
and has a chute connected to a variable vibrator, which is regulated
via the dedicated feed controller. The feed from each hopper is
conveyed along a main vibratory chute which directs the feed to
a port located in the roof and/or a hollow electrode (for centre feeding).
Power is supplied by means of an 11 kV supply
from a substation, which is isolated from the facility by a manual
isolator and an electrically operated vacuum breaker. Power (DC)
is provided by means of a thyristor drive rated at 750 V/1800 A.
The incoming secondary supply is switched to the thyristor unit
by circuit breakers. The thyristor drive is supplied with chokes
used for smoothing the current output to obtain a stable arc.
Control and data acquisition
The DC-arc furnace is fully controlled using a PC-based
SCADA (Supervisory Control And Data Acquisition) system, which
provides a console for the configuration of operating parameters,
recipe management, alarm annunciation, and data logging. Manual
or semi-automatic operation is also available.
The off-gases are extracted by a reversed pulse bagplant
rated at 6 500 Nm³/h. The off-gas is extracted
from the furnace through the gas extraction port situated in the
furnace roof. The bagplant utilizes 100 polyester needlefelt bags
with a total area of 100 m². The fume released from
the bags settle into a cone, from where it is continuously discharged
through a rotary valve into drums.
Pyrometallurgy Division, Mintek,
200 Hans Strijdom Drive, Randburg, 2125, South Africa
Private Bag X3015, Randburg, 2125, South Africa.
Phone: +27 (11) 709-4642
Fax: +27 (11) 793-6241
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Copyright © 1996-97 George la Grange, Mintek, firstname.lastname@example.org
7 October 1997