text: The third commercial copper ISASMELT plant was installed in MIM's Mount Isa copper smelter at a cost of approximately A$100 million. It was designed to treat 104 t/h of copper concentrate, containing 180,000 t/y of copper, and it began operation in August 1992.
  A significant difference between the Mount Isa copper ISASMELT plant and all the others is that it uses an Ahlstrom Fluxflow waste heat boiler to recover heat from the furnace waste gas. This boiler uses a recirculating fluid bed of particles to rapidly quench the gas as it leaves the furnace, and then uses the enhanced heat transfer properties of solid–solid contact to cool the particles as they are carried past boiler tubes that are suspended in a shaft above the bed. The high heat transfer rate means that the Fluxflow boiler is relatively compact compared with conventional waste heat boilers and the rapid cooling of the waste gas limits the formation of sulfur trioxide ("SO"), which in the presence of water forms sulfuric acid that can cause corrosion of cool surfaces.
  In its early years, the Fluxflow boiler was the cause of significant down time, because the rate of wear of the boiler tubes was much higher than expected. The problems were solved by understanding the gas flows within the boiler and redesigning the boiler tubes to minimise the effects of erosion.
  The life of the refractory bricks in the ISASMELT furnace was initially shorter than expected and a water cooling system was briefly considered to extend them; however, this was not installed and operational improvements resulted in a significant extension of the lining life without this capital and operating expense. Since 1998, the refractory lining lives have exceeded their two-year design, with lives of the 8th and 9th linings nearly reaching three years. The most recent lining lasted for 50 months, with the one before that lasting for 44 months.
  In the first years of operation at Mount Isa, the throughput of the ISASMELT furnace was constrained by problems with some of the ancillary equipment in the plant, including the boiler, slag granulation system and concentrate filters. The ultimate constraint was the decision during its construction to keep one of the two reverberatory furnaces on line to increase the copper smelter production to 265,000 t/y of anode copper. The smelter's Peirce-Smith converters became a bottleneck and the feed rate of the ISASMELT furnace had to be restrained to allow sufficient matte to be drawn from the reverberatory furnace to prevent it freezing solid. The ISASMELT 12-month rolling average of the feed rate fell just short of 100 t/h for much of this period, not quite reaching the design annual average of 104 t/h. MIM decided to shut down the reverberatory furnace in 1997, and the ISASMELT plant 12-month rolling mean feed rate quickly exceeded the 104 t/h design when this constraint was lifted.
  The performance of the ISASMELT plant was sufficiently encouraging that MIM decided to expand the ISASMELT treatment rate to 166 t/h by adding a second oxygen plant to allow higher enrichment of the lance air. As a result, by late 2001 it had achieved a peak rate of 190 t/h of concentrate, and the smelter produced a peak annual total of 240,000 t of anode copper. At that time, the Mount Isa copper smelter, together with its copper refinery in Townsville, was among the lowest cost copper smelters in the world.
  Lance life is typically two weeks, with lance changes taking 30 to 40 minutes, and repairs usually being limited to replacement of the lance tips.
  In 2006, MIM commissioned a second rotary holding furnace that operates in parallel with the existing holding furnace.