Rotary kilns are furnaces that come in inclined cylindrical shape and have rotating mechanism. The kilns are used to heat solids to the point of chemical reaction through dry or wet process. The rotating inclined cylinder is fired from one end to generate heat along its length. The kilns are usually direct fired and come lined with refractory material to offer protection to steel shell and to achieve a reduction in radiation losses and to transfer heat to the material.
The working of kiln is like heat exchanger in which heat is transferred in several ways, for instance through convection, radiation and conduction. The fuel types used to fire kiln are petroleum coke, ground coal, fuel oils and gases. With the kiln rotation, the processed material travels towards discharge end.
- Rotary kiln has cylindrical shell supported on two/more tyre stations on supporting rollers.
- One tyre comes fixed axially through set of thrust rollers to counter thrust load at the time of kiln movement and thus preventing shifting kiln from its axis.
- Drum assembly along with tyres rotates making use of girth gear and pinion arrangement.
- Common prime movers used are gear reducers to reduce speed or increase torque as needed.
- Girth gears are mounted on tangential spring plates attached to shell to compensate thermal expansion.
- Driving pinion comes mounted on output shaft of worm/helical gear unit.
- Use of several kinds of bearings on kiln with high loads.
- Shell diameter and length are designed to suit specific products and production capacities.
- Suitable sealing arrangement prevents ambient air from entering process.
- Suitable refractory lining provides working as high temperature and abrasive material wear resistant lining.
- Firing system works as an important part of rotary kiln system and optimizes combustion of fuels to release heat in kiln.
- The cyclone type dust collection arrangement finds use as a pollution control measure.
Rotary kilns find use in the production of
- Sponge iron
- Construction materials
- Petroleum coke