Rotary Kilns are used to heat solids to the point where a required chemical reaction(s) takes place. The Rotary Kiln is basically a rotating inclined cylinder, solids retention time in the kiln is an important factor and is set by proper selection of diameter, length, speed, slope and the internal design. Calculations are the process where material is being heated to the desired temperature at which physical and chemical is being continuous type of process. This contain have long shell supported on tyres and driven by Girth gear, pinion gear and gear box. The size of the Kiln is designed on the basis of the properties of the material because the rate of heat transfer depends very much on the diameter, length, speed of the shell; slope of the shell and even on the thickness of the refectory. The heating inside the kiln takes place by convection, radiation and conduction. Hence the type and size of the flame is also very important so high quality burner should be use for the kiln.
Usually flames are being injected through the burner pipe in the opposite direction of the flow of the material called counter current, while sometime it flows in the same direction of flow of material and called co-current process. It all depends upon the required temperature, which varies from 3500 C to 11000 C. Usually the fuel for firing is oil, gas or the pulverized coal.