por He rotary dryer It is a type of dryer used in the industry to reduce the water content in materials. Rotation facilitates the exposure of the material to heat sources that increase its temperature, which helps to eliminate or reduce its water content.
Rotary dryers are made up of a rotating metal cylinder or drum that has a slight inclination to facilitate the discharge of the material from the dryer. The dryer is mounted on a concrete base or steel beams for support.
The material is dried thanks to a current of hot air, produced by a combustion oven. The hot air current passes through the wet material, flowing along the rotary dryer, thus increasing the temperature of the material and the loss of its moisture.
The rotary dryer is used to dewater metallic and non-metallic minerals, such as clay and coal from coal mines. It is also used for drying rice, citrus peels, orange pulp, vegetable trimmings and alfalfa feed.
[toc]
Rotary Dryer Operation
overall process
The material to be treated enters the rotary dryer at the top and comes out, once treated to reduce its humidity, at the bottom. This process is favored due to the slight inclination of its support. The wall is endowed with a kind of fins that form an angle with it.
Material entering the top of the dryer tends to fall to the bottom of the dryer. However, the rotation in combination with the fins that it has on its wall, produces the elevation of the material to be dried until it reaches a certain height on the internal wall.
There the fins are not capable of supporting the material they carry and it falls towards the bottom of the dryer, passing through a current of hot air that causes the loss of moisture from the material. This process is repeated several times until the desired drying of the wet material is achieved.
Drying of wet material
direct heating
Hot air is produced by the mixture of a current of air and the gases produced in a combustion furnace. When the heating of the humid material is a consequence of the direct action on it of the combustion gases, then it is called direct heating.
The hot air stream can be directed from the discharge site to the loading site of the rotary dryer; that is, the hot air moves in the opposite direction to that followed by the falling material. In this case, we speak of a countercurrent flow of hot air.
Also the hot air current can be directed from the loading site of the rotary dryer towards the unloading site. In other words, the hot air and the material that falls through the dryer have the same orientation, speaking in this case of a parallel flow of hot air.
indirect heating
In some rotary heaters the air stream is preheated, heating the wet material without the intervention of combustion gases. In this case, we speak of indirect heating.
Evaporation and rotation
There are drum dryers, or rotary dryers, in which the evaporation of water on the inner wall occurs due to its heating. Meanwhile, a metal blade scrapes away the solid material that is attached to the wall.
The dried material then descends by gravity towards the outlet of the rotating drum, functioning as a hybrid of a dryer and an evaporator.
What is a rotary dryer used for?
The utility of rotary dryers is very wide, although its most widespread use is the drying of various materials including sludge of different origins, cereal grains, feed for dairy cattle, pigs and poultry, etc.
Rotary dryers are also used in some chemical reactions, in the mixing of materials, in the recovery of solvents, agglomeration of solids. They can also be used in roasting nuts, sesame seeds and cocoa beans.
parties
Drum
The drum, cylinder or casing of the rotary dryer is metallic and usually has a kind of fins that intervene in the mobilization of the material present inside. It is the drying site of the wet material.
loading site
Found on the top of the rotary dryer, since it has a slight inclination.
download site
Found in the lower part of the rotary dryer, which favors the output of the processed material.
Medium
A concrete or steel beam support that gives the rotary dryer its inclination. There are some dryers in which the degree of inclination can be adjusted depending on favoring the output of the treated material.
Electric motor
An electric motor with a transmission system that acts by producing the rotation of the drum of the rotary dryer.
combustion furnace
An oven or a combustion burner that produces gases, which when mixed with an air current, originate a flow of hot air. This constitutes the main source of heating the wet material, thus producing the evaporation of the water content.
gas eliminator
A part that intervenes in the elimination of gases that are produced in the rotary dryer.
Applications
raw material processing
The rotary dryer is used for drying clay in industrial cement, as well as for coal sludge from mines. It is also used in the drying of sandstone, powdered minerals, mineral slag and the treatment of mud of different origins and characteristics.
For example, rotary dryers are used to dewater textile sludge, papermaking sludge, electroplating sludge, oil sludge, wastewater sludge, etc. They are also used in the elimination of moisture from diatomaceous earth, kaolin, chloride and potassium sulfate.
In addition, rotary dryers are used to dry lime milk, phosphate rock slag and red mud from aluminum plants.
Treatment of biological and organic material
Rotary dryers are used for the treatment of animal manure, wood dregs, citrus peels, vegetable trimmings, alfalfa feed, rice with a high moisture content, used orange pulp to complete the feeding with cereals of breeding animals.
Some dryers can use very hot air that can be used to roast seeds.
References
Whitten, Davis, Peck & Stanley. (2008). Chemistry. (8th ed.). CENGAGE Learning.
Wikipedia. (2020). Rotary dryer. Retrieved from: en.wikipedia.org
Lisboa, MH, Vitorino, DS, Delaiba, WB, Finzer, JRD, & Barrozo, MAS. (2007). A study of particle motion in rotary dryer.Brazilian Journal of Chemical Engineering, 24(3), 365-374. doi.org/10.1590/S0104-66322007000300006
Elsevier BV (2020). Rotary dryer. Science Direct. Retrieved from: sciencedirect.com
Zonelion Taeda. (nd). Rotary Drum Drying Machine. Retrieved from: hntaida.com