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A rotary dryer is an industrial dryer used to reduce or minimize the moisture content of the material being processed by exposing it to heated gas.A dryer consists of a rotating cylinder ("drum" or "housing"), a drive mechanism, and a supporting structure (usually concrete columns or a steel frame).The barrel is slightly inclined, and the discharge end is lower than the feed end, so that the material passes through the dryer under the action of gravity.Material to be dried enters the dryer and as the dryer rotates, the material is lifted by a series of fins (called vanes) that line the inside walls of the dryer.When the material gets high enough, it falls back to the bottom of the dryer and travels through the thermals as it falls.
Rotary dryers have many applications, but are most commonly found in the mineral industry for drying sand, stone, soil and ore.They are also used in the food industry for granular materials such as grains, grains,beans and coffee beans.
A variety of spin dryer designs are available for different applications.Airflow, heat source, and drum design all affect a dryer's efficiency and suitability for different materials.
The hot gas flow can move from the feed end to the discharge end (called co-current flow) or from the discharge end to the feed end (called counter-current flow).The direction of the airflow combined with the inclination of the drum determines how quickly the material moves through the dryer.
The gas stream is most often heated by burners using gas, coal or oil.A dryer is said to be "direct heated" if the hot gas stream consists of a mixture of air and combustion gases from the burner.Alternatively, the gas stream may consist of air or another (sometimes inert) gas preheated.Where the burner combustion gases do not enter the dryer, the dryer is said to be "indirectly heated". When product contamination is a concern, indirect heated dryers are often used.In some cases, a combination of direct-indirect heated rotary dryers is also used to increase overall efficiency.
A spin dryer can consist of a single shell or multiple concentric shells, but usually no more than three shells are required.Multiple rollers can reduce the amount of space required for equipment to achieve the same throughput.Multiple tumble dryers are usually directly heated by oil or gas burners.The addition of a combustor at the feed end helps ensure efficient fuel use and uniform drying air temperature.
Some rotary dryers have the ability to combine other processes with drying.Other processes that can be combined with drying include cooling, cleaning, shredding and separation.
Industrial dryers are used to efficiently process large quantities of bulk materials that require reduced moisture content.Depending on the amount and composition of the material that needs to be dried,industrial dryers come in many different models, specifically constructed for the type and amount of material being processed.The most common types of industrial dryers are fluid bed dryers, rotary dryers, rolling bed dryers, conduction dryers, convection dryers, pharmaceutical dryers, suspension/paste dryers, annular bed or TORBED dryers and dispersion dryer.Various factors are considered when determining the correct dryer type for any given application, including the material to be dried,drying process requirements, production requirements, end product quality requirements and available facility space.