1 ton / day Pilot Plant
(200 kVA DC-arc facility)

Schematic presentation of 200kVA DC-arc furnace The 1 ton / day DC-arc facility consists of:

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 roof.


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.

Feed system

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 supply

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.

Gas handling

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.

Contact Information
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


Copyright © 1996-97 George la Grange, Mintek,
7 October 1997