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The rotary kiln was invented in 1873 by Frederick Ransome. [1] He filed several patents in 1885-1887, but his experiments with the idea were not a commercial success. Nevertheless, his designs provided the basis for successful kilns in the US from 1891, subsequently emulated worldwide.
Rotary lime kiln (rust-colored horizontal tube at right) with preheater, Wyoming, 2010 Traditional lime kiln in Sri Lanka. A lime kiln is a kiln used for the calcination of limestone (calcium carbonate) to produce the form of lime called quicklime (calcium oxide). The chemical equation for this reaction is CaCO 3 + heat → CaO + CO 2
Lightweight expanded clay aggregate (LECA) or expanded clay (exclay) is a lightweight aggregate made by heating clay to around 1,200 °C (2,190 °F) in a rotary kiln. The heating process causes gases trapped in the clay to expand, forming thousands of small bubbles and giving the material a porous structure.
Rotary kilns run 24 hours a day, and are typically stopped only for a few days once or twice a year for essential maintenance. One of the main maintenance works on rotary kilns is tyre and roller surface machining and grinding works which can be done while the kiln works in full operation at speeds up to 3.5 rpm.
Calcination is thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O 2 fraction of air), generally for the purpose of removing impurities or volatile substances and/or to incur thermal decomposition.
The Waelz process is a method of recovering zinc and other relatively low boiling point metals from metallurgical waste (typically electric arc furnace flue dust) and other recycled materials using a rotary kiln (waelz kiln). The zinc enriched product is referred to as waelz oxide, and the reduced zinc by product as waelz slag.
In general, the rotary kilns used to chemically combine the raw materials are operated at a higher peak temperature (1600°C) than that required for gray clinker manufacture (1450°C). This requires a higher fuel consumption (typically 20-50% more), and results in lower kiln output (typically 20-50% less) for a given sized kiln.
Reduction is performed in a rotary kiln with pseudobrookite (Fe 2 O 3.TiO 2), coal, and sulfur, then heated to a temperature greater than 1200 °C. [11] The iron oxide in the mineral grains is reduced to metallic iron to produce reduced ilmenite: Fe 2 O 3 ·TiO 2 + 3 CO → 2 Fe + TiO 2 + 3 CO 2