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ROTARY DRYER :
The Rotary Dryer is a type of industrial dryer employed to reduce or to minimize the liquid moisture content of the material it is handling by bringing it into direct contact with a heated gas to evaporate the water. Rotary Dryers are suitable for drying of a wide range of materials continuously because of its ability to process materials having considerable variation in size and composition.
Despite the introduction of new technologies the long-established Rotary Dryer is still widely regarded as the workhorse of many process industries. The robust yet simple construction combines flexibility with reliability enabling this type of dryer to handle a vast range of materials.
ROTARY DRYER CONSTRUCTION :
. The dryer is made up of a large rotating cylindrical tube, supported by two nos. riding rings(tyres) running over a set of support rollers with a stationary feed and a discharge hood, mounted over a channel frame with suitable sealing arrangement between the shell ends and hoods. The dryer slopes slightly so that the discharge end is lower than the material feed end in order to convey the material through the dryer under gravity. Fabricated in carbon, stainless steel, and MS+rubber lined with flights or lifters are welded or bolted internally to produce the cascade of particles falling through hot gas stream. The mechanical lifting of the material allows to dry off the materials from filter cake to coarse minerals through the hot gas stream, also helps in breaking-up lumps for uniform drying. The length of the drum may range from 4 to 10 times of its diameter and usually operates with 12 to 15% of their volume filled with the material. The Hot Air Generator, the feeding equipment and the dust collection types of equipment like cyclone and bag filter are the part of the Rotary Dryer system.
PRINCIPLE OF OPERATION:
The principle of operation is based on showering or cascading the wet material through a hot stream, flowing either co-current or counter-current to the solids. The hot gas induces the evaporation of the moisture. The heat lost to the material and evaporation of water vapor reduces the gas temperature rapidly, such that it leaves the dryer at a comparatively low temperature.
The efficiency of the dryer is largely dependent on the differential on the differential between the inlet and exhaust temperatures, although the heat transfer rate is also influenced by the relationship between the design of flights and the speed of rotation. However, irrespective of the gas and material temperature, the drying or residence time may be critical, as this is governed by the rate of diffusion of water from the core to the surface of the material.
Rotary dryer adopts the direct flow type of heating with heat source from the heat exchanger. The material to be dried enters the rotating dryer shell, in a regulated way through a screw feeder, and through a feed chute attached with the feed hopper, is mounted over the stationary feed hood. As the dryer is installed in slope the material flows to the back end under gravity and rotation force and is lifted by lifters repeatedly and thrown down, which make the material form even curtain and exchange heat sufficiently with the inner heat flow and repeated scattering. The water separated by the hot air flow is changed into vapor and discharged into the atmosphere either directly or through a dust collection system. The dried material is discharged from the other end of the shell through a stationary discharge hood.
HEATING SYSTEM :
In both co-current and counter-current systems, the material when drying or pre-heating which are unaffected by heat or exposure to a flame, an oil or gas burner is used to fire directly into the drum. For low temperature and heat-sensitive applications, indirectly heated air can be supplied via an external steam tube type exchanger and induced by a centrifugal fan located at up steam of the air heater with a filter at fan inlet.
AIR HANDLING SYSTEM:
In Rotary Dryer the flow of air is induced by a centrifugal fan located at upstream of the air heater and the exhaust air is removed either direct at the outlet or by a second centrifugal fan at the outlet through Dust Collector.
DUST COLLECTION SYSTEM:
The choice of dust collection equipment will vary according to the application, but in addition to the range of high efficiency and high capacity cyclones, a bag filter is used.
MATERIAL OF CONSTRUCTION: Carbon Steel, Stainless Steel & MS+Rubberlined.

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