5 ton / day Pilot Plant
(3.2 MVA DC-arc facility)
The 5 ton / day DC-arc facility consists of:
- DC-arc furnace (3.0 kA max)
- Feed system (1 t/h max)
- Off-gas handling plant (6 500 Nm³/h)
- Power supply 2 x 1.6 MVA transformer/rectifiers
- Control, instrumentation and data logging systems
Tapping the 3.2 MVA furnace
Description of the pilot plant
The furnace consists of a refractory-lined cylindrical shell, a conical roof and a small flat roof positioned on top of the 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 roofs are lined with a castable refractory. The furnace is equipped with water-spray cooling on the sidewalls and with water cooling jackets on the roofs.
A graphite electrode with an outer diameter of 125 mm is used as cathode The electrode enters the furnace through the centre port in the flat roof. This electrode port consists of a 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, via radially extending arms, to the furnace shell and then to the anode cable.
The feed system consists of six 0.9 m³ hoppers mounted on load cells, vibratory feeders positioned under the hoppers, a belt conveyor, a bucket elevator and two final feed hoppers. One final feed hopper is fitted with a screw feeder feeding the feed through a telescopic pipe down the central hole in the electrode (centre feeding); the other is fitted with a vibratory feeder that directs the material into three pipes connected to feed ports in the flat roof.
Power is supplied to the facility 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 two thyristor drives rated at 750 V/1800 A. The incoming secondary supply is switched to the thyristor units by circuit breakers. The thyristor drives are supplied with chokes used for smoothing the current output to obtain a stabile 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 gases are extracted through the off-gas port in the conical 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 or bags.
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, email@example.com
7 October 1997