WHAT IS A ROTARY DRYER ?
Rotary dryer is one of the most widely used dryers that are used to
dry various chemicals, minerals, food. These dryers are based on
rotary ovens designed and upgraded by English Ransom in 1885. These
dryers are composed of metal pipes with a diameter of 60 to 300 cm
and a length of 6 to 24 meters, which are placed on rollers and
rotate with a gentle slope around the horizontal
ridge.
Agricultural and vegetable wastes such as beet pulp, sugarcane
pulp, tomato pulp and citrus peel are among the plant and
agricultural materials that are used by rotary dryers to produce
animal feed. In the chemical industry, rotary dryers are used to
dry iron sulfate, manganese carbonate, zinc carbonate, zinc
sulfate, etc. Also, in the production of asphalt, a rotary dryer is
used to dry and heat the sand in the asphalt.
Rotary steel dryer
Rotary steel dryer is used in some cases that require drying of
chemicals or food. For example, in the case of drying chemicals
such as zinc sulfate or crystalline manganese that have an acidic
pH, the presence of acidic wet material with iron metal, causes
corrosion of the inner surface of the dryer, wear of the device and
most importantly contamination of the material inside the dryer,
iron element And their quality and price will decrease. Therefore,
in such cases, it is necessary to use a rotary dryer with a steel
surface. 304 steel alloys (for food), 310 (for materials that need
to be dried or baked at high temperatures, 316 (for chemicals) are
used in the manufacture of steel dryers.
How the rotary dryer works?
Drying of materials in rotary dryers is done by the presence of wet
materials with hot and dry air produced by a burner or gas heater
or diesel burner. Materials from the upper part of the dryer After
the wet material enters the rotary dryer, the materials are exposed
to hot air produced by the burner and dry by rotating the dryer
tube with the help of gravity and metal blades angled downwards.
They move and dry along the path in the dryer tube and gradually
lose moisture and finally leave the machine. The installation of
spoons causes better turning of the material and better stirring
and more hot air contact with the material and helps the material
to dry faster and better.
In iron-walled dryers, it is possible to increase the temperature
of the material up to 250 degrees, and to apply higher
temperatures, it will be necessary to use a refractory steel dryer
or a refractory wall dryer.
If there is a need to apply indirect heating to the material, heat
should be given to the outer body of the dryer tube and after the
dryer wall is heated, the material inside the dryer tube should be
dried.
Hot air entering the rotary dryer may enter the dryer either in the
same direction or in the opposite direction.
A dust trap or bag filter is used to prevent material wastage and
to prevent environmental pollution, and the centrifugal fan will
help create airflow in the dryer
Types of rotary dryers in terms of the direction of material and
hot air passage
Co-Current
The direction of passage of material and hot air is the same. In
this case, cold and wet materials along with hot air enter the
machine from the dryer inlet side and constantly move away from the
heat source. This mode is better for when there is no need for
complete drying and also when the material is sensitive to
temperature and there is a possibility of burning and changing the
color or chemical nature of the material. For example, drying
bentonite and kaolin will be better in this way due to the
sensitivity of these materials to high heat and also due to the
fact that there is no need to completely dry these materials. Or,
for example, if manganese carbonate is exposed to a temperature of
more than 90% Celsius, it will change color from light pink to
brown, so it is better to use a rotary dryer to dry
it.
Counter-current
The direction of passage of materials and hot air is opposite. In
this case, the material enters the machine from the inlet side of
the dryer and the burner are installed at the end of the machine.
The material is constantly getting closer to the heat source and
finally exits the dryer. This type of design is suitable for
materials that are not sensitive to heat, and the aim is to dry the
materials as much as possible.