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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.
View of the six rotary furnaces at the Essen–Borbeck direct reduction plant, c. 1964. The Krupp–Renn process was a direct reduction steelmaking process used from the 1930s to the 1970s. It used a rotary furnace and was one of the few technically and commercially successful direct reduction processes in the world, acting as an alternative to ...
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.
It can also play an active part in the chemical reaction by ensuring mixing between the reactants present. Rotary hearth processes, where the ore rests on a fixed bed and travels through a tunnel, fall into the first category. Rotary kiln processes, where the ore is mixed with coal at high temperature, constitute the second category.
The multiple hearth furnaces consist of several circular hearths or kilns superimposed on each other. Material is fed from the top and is moved by the action of rotating "rabble arms", and the revolving mechanical rabbles attached to the arms move over the surface of each hearth to continuously shift the ore.
The earliest successful rotary kilns were developed in Pennsylvania around 1890, based on a design by Frederick Ransome, [5] and were about 1.5 m in diameter and 15 m in length. Such a kiln made about 20 tonnes of clinker per day.
The Japanese noborigama kiln is an evolution from anagama design as a multi-chamber kiln where wood is stacked from the front firebox at first, then only through the side-stoking holes with the benefit of having air heated up to 600 °C (1,100 °F) from the front firebox, enabling more efficient firings.
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.