The ISASMELT process is an energy-efficient smelting process that was jointly developed from the 1970s to the 1990s by Mount Isa Mines (a subsidiary of MIM Holdings and now part of Glencore) and the Government of Australia's CSIRO. It has relatively low capital and operating costs for a smelting process. ISASMELT technology has been applied to lead, copper, and nickel smelting. As of 2021, 22 plants were in operation in eleven countries, along with three demonstration plants located at Mt Isa. The installed capacity of copper/nickel operating plants in 2020 was 9.76 million tonnes per year of feed materials and 750 thousand tonnes per year across lead operating plants. Smelters based on the copper ISASMELT process are among the lowest-cost copper smelters in the world.
The ISASMELT furnace An ISASMELT furnace is an upright-cylindrical shaped steel vessel that is lined with refractory bricks. There is a molten bath of slag, matte or metal (depending on the application) at the bottom of the furnace. A steel lance is lowered into the bath through a hole in the roof of the furnace, and (possibly oxygen-enriched) air is injected through the lance, causing vigorous agitation of the bath.
Mineral concentrates or materials for recycling are dropped into the bath through another hole in the furnace roof or, in some cases, injected down the lance. These feed materials react with the oxygen in the injected gas, resulting in an intensive reaction in a small volume (relative to other smelting technologies). ISASMELT lances contain one or more devices called "swirlers" that cause the injected gas to spin within the lance, forcing it against the lance wall, cooling it. The swirler consists of curved vanes around a central pipe forming an annular flow. They are designed to minimize pressure losses changing the angle from axial to tangential thus creating a strong vortex. The vortex helps mix liquids and solids with oxygen in the bath. The cooling effect results in a layer of slag "freezing" on the outside of the lance. This layer of solid slag protects the lance from the high temperatures inside the furnace. The tip of the lance that is submerged in the bath eventually wears out, and the worn lance is easily replaced with a new one when necessary. The worn tips are subsequently cut off and a new tip welded onto the lance body before it is returned to the furnace. ISASMELT furnaces typically operate in the range of 1000–1200 °C, depending on the application. The refractory bricks that form the internal lining of the furnace protect the steel shell from the heat inside the furnace. The products are removed from the furnace through one or more "tap holes" in a process called "tapping". This can be either continuous removal or in batches, with the tap holes being blocked with clay at the end of a tap, and then reopened by drilling or with a thermic lance when it is time for the next tap. The products are allowed to separate in a settling vessel, such as a rotary holding furnace or an electric furnace. While smelting sulfide concentrates, most of the energy needed to heat and melt the feed materials is derived from the reaction of oxygen with the sulfur and iron in the concentrate. However, a small amount of supplemental energy is required. ISASMELT furnaces can use a variety of fuels, including coal, coke, petroleum coke, oil and natural gas. The solid fuel can be added through the top of the furnace with the other feed materials, or it can be injected down the lance. Liquid and gaseous fuels are injected down the lance.
Advantages of the ISASMELT process
The advantages of the ISASMELT process include:
High productivity with a small footprint: Glencore's copper smelter in Mount Isa treats over 1 million t/y of copper concentrate through a single furnace 3.75 m in diameter. The small footprint makes the process well suited to retrofitting to existing smelters where there are significant space constraints Simple operation: the ISASMELT furnace does not require extensive feed preparation as the feed can be discharged from a belt conveyor directly into the furnace high energy efficiency: installing an ISASMELT furnace in the Mount Isa copper smelter reduced energy consumption by over 80% (through better use of the inherent energy contained in the sulfide concentrate) compared with the roaster and reverberatory furnaces previously used there Flexibility in feed types: ISASMELT furnaces have been used to smelt copper, lead and nickel concentrates with a wide range of compositions, including high levels of magnetite, and secondary materials, such as copper scrap and lead-acid battery paste Flexibility in fuel types: ISASMELT furnaces can operate with a variety of fuels, including lump coal of varying ranks, coke (lump or fine), petroleum coke, oil (including recycled oil), natural gas, and liquid petroleum gas, depending on which is the most economic at the smelter's location High turn-down ratio: the feed rate to a single ISASMELT installation can easily be scaled up or down, depending on the availability of concentrate and the needs of the smelter Low feed carry over: ISASMELT furnaces typically lose about 1% of the feed as carry-over with the waste gas, meaning less material needs to be returned to the furnace for retreatment Effective containment of fugitive emissions: because the furnace has only two openings at the top, any fugitive emissions can easily be captured High elimination of deleterious minor elements: due to the flushing action of the gases injected into the ISASMELT furnace slags, copper ISASMELT furnaces have a high elimination of minor elements, such as bismuth and arsenic, that can have deleterious effects on the properties of the product copper High sulfur dioxide concentration in the waste gas: the use of oxygen enrichment gives the ISASMELT plants high sulfur dioxide concentrations in the waste gas stream, making acid plants cheaper to build and operate Relatively low operating cost: the energy efficiency of the process, the simple feed preparation, the relative lack of moving parts, low feed carry-over rates, low labour requirements and the ease of replacing lances and refractory linings when they are worn give the ISASMELT process relatively low operating costs Relatively low capital cost: the simplicity of the construction of the ISASMELT furnaces and the ability to treat concentrate without drying make it cheaper than other smelting processes.
History of the process
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