The ISASMELT™ furnace is a vertical steel cylinder that is lined with high quality refractory bricks. Air, oxygen and fuel are injected through the ISASMELT™ lance into a molten slag bath. The injected materials react with metal-bearing raw materials in the slag bath, producing a slag and a semi-finished product, which can be copper matte, blister copper or lead bullion.
Feed preparation is generally limited to mixing of the raw materials (concentrate, flux and coal) with some water in a mixer or pelletiser. The moist feed is then conveyed to the furnace and dropped into the furnace through a port in the roof.
The ISASMELT™ lance is specially designed to operate in the aggressive furnace environment. Wear of the steel lance tip is inhibited because of its special design. A frozen slag layer forms on its exterior., The lance is subjected every few weeks to minor maintenance, including replacement of a small part of the tip. The lance is designed to operate with low pressure (<150kPa) air, reducing the cost of blower systems.
Off Gas System
The off gases from the reactions in the bath pass through an outlet in the furnace roof into the off gas system, that generally comprises a waste heat boiler followed by conventional gas cleaning equipment. The off gas, which has a high SO2 content, is treated in a sulfuric acid plant for removal of sulfur prior to discharge to atmosphere.
The products are removed from the base of the furnace through a water cooled taphole. They are generally separated in a settling furnace prior to further treatment.
The furnace design is elegant and has been developed over many years to minimise the capital and operating costs, as well as the down time required for maintenance. The cylindrical design allows it to be bricked easily without the need for mortar and with very tight tolerances. It is not necessary to use water cooling in the furnace walls.
Sophisticated process control systems have been developed in the Mount Isa operations over more than 15 years that ensure the furnace operates smoothly with minimal need for operator involvement.