Sinter plants agglomerate iron ore fines (dust) with other fine materials at high temperature, to create a product that can be used in a blast furnace. The final product, a sinter, is a small, irregular nodule of iron mixed with small amounts of other minerals. The process, called sintering, causes the constituent materials to fuse to make a single porous mass with little change in the chemical properties of the ingredients. The purpose of sinter are to be used converting iron into steel.
Sinter plants, in combination with blast furnaces, are also used in non-ferrous smelting. About 70% of the world's primary lead production is still produced using the sinter plant–blast furnace combination, and this combination was formerly often used in copper smelting (at the Electrolytic Refining and Smelting smelter in Wollongong, New South Wales, for example).
Many countries, including india, France and Germany, have underground deposits of iron ore in dust form (blue dust). Such iron ore cannot be directly charged in a blast furnace. In the early 20th century, sinter technology was developed for converting ore fines into lumpy material chargeable in blast furnaces. Sinter technology took 30 years to gain acceptance in the iron-making domain, but now plays an important role. Initially developed to generate steel, it is now a means of using metallurgical waste generated in steel plants to enhance blast furnace operation and reducing waste.
Preparation of the ores
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Sintering the material
Material is put on a sinter machine in two layers. The bottom layer may vary in thickness from 30 to 75 millimetres (1.2 to 3.0 in). A 12 to 20 mm sinter fraction is used, also referred to as the hearth layer. The second, covering layer consists of mixed materials, making for a total bed height of 350 to 660 millimetres (14 to 26 in). The mixed materials are applied with drum feeders and roll feeders, which break the nodules into similar sizes. The upper layer is smoothed using a leveler. The material, also known as a charge, enters the ignition furnace into rows of multi-slit burners. In the case of one plant, the first (ignition) zone has eleven burners. The next (soaking/annealing) zone typically offers 12 burners.
The temperature is typically maintained between 1,150 and 1,250 °C (2,100 and 2,280 °F) in the ignition zone and between 900 and 1000 °C in the soaking zone to prevent sudden quenching of the sintered layer. The top 5 mm from screens goes to the conveyor carrying the sinter for the blast furnace and, along with blast furnace grade sinter, either goes to sinter storage bunkers or to BF bunkers. Blast furnace-grade sinter consists of particles sized 5 to 12 mm as well as 20 mm and above.
There are certain advantages of using sinters as opposed to using other materials which include recycling the fines and other waste products, to include flue dust, mill scale, lime dust and sludge. Processing sinter helps eliminate raw flux, which is a binding material used to agglomerate materials, which saves the heating material, coke, and improves furnace productivity.
Improvements and efficiency can be gained from higher softening temperature and narrower softening in the melting zone, which increases the volume of the granular zone and shrinks the width of the cohesive zone. A lower silica content and higher hot metal temperature contributes to more sulphur removal.
- R J Sinclair, The Extractive Metallurgy of Lead (The Australasian Institute of Mining and Metallurgy: Melbourne, 2009), 9–12.
- P J Wand, "Copper smelting at Electrolytic Refining and Smelting Company of Australia Ltd., Port Kembla, N.S.W.", in: Mining and Metallurgical Practices in Australasia: The Sir Maurice Mawby Memorial Volume, Ed J T Woodcock (The Australasian Institute of Mining and Metallurgy: Melbourne, 1980) 335–340.