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Different types of cleaners used in grain processing and their performance evaluation
(AGRI. ENGG. AND TECH.)
2. De awner
3. Fanning mill
4. Air screen cleaner
5. Specific Gravity separator
6. Indented cylinder separator
7. Cyclone Separator
8. Pneumatic separator
9. Inclined draper
10. Electrostatic separator
11. Magnetic separator
A scalper can be used to rough
clean seed when trash content is
The scalper basically consists of a
vibrating or rotating screen or
The screen perforations are large
enough to allow the rough seed
to pass through readily while
large inert material is scalped off
and removed from the seed lot.
Some of the high moisture
particles may be removed
Normally much higher output
than ﬁne cleaning
Before air screen cleaner
Optional, it can be bypassed
Seed ﬂows much better in rest of
Important when mechanical
planting machines are used
May be important for breaking
dormancy in some species
Screen cleaners that employ an air blast
to assist in cleaning is known as fanning
these are used for cleaning but these are
not effective as regards to density and if
the materials have the
same or nearly the same shape. Here in
addition to the aspirating fan used to
draw air through the
material fed on 1st screen unit, another
fan is used to force the air through the
product after fine grading
AIR SCREEN CLEANER
A common air screen cleaner for processing seed uses two air blasts and two screens.
The first air system removes dust and light chaff before the seed reaches the first
The first screen allows the good seed to drop onto the second screen. The large
foreign material rides over the first screen and is discarded.
The second screen is a grading screen
Uses three cleaning systems; aspiration, scalping screen and grading lower screen
Classified into two types based on the movement of the screening surface
• Vibratory screen cleaner
• Rotary screen cleaner
Vibratory screen cleaner
Screening unit is composed of double or multiple
Screens are tightened together and suspended in such
a manner that these have horizontal oscillating and
slightly vertical motion.
The slope of the screen is adjustable to control the
rate of forward travel of the grain
To avoid clogging, the screens are fitted with brush
Two screen m/c fitted with aspirator to suck the
Coarse impurities are screened off by upper screen
Fine impurities are screened off by lower screen
Grains are again cleaned by upward draft of air in the
During this process, remaining lighter impurities and
shriveled grains are sucked away
Lighter impurities are removed by Cyclone separator
Rotary air screen cleaner
Has normally circular decks
Motion is circular in horizontal plane
Either single or double drum
Consists of a rotary screen, aspirator and
Sound grains pass through the screen
perforation into the center of the screen
drum. Oversized material is retained above
and pass out through an outlet.
Sound grains come out at the center side of
the drum rotating at low speed and fall onto
the vibratory screen which remove the dirt
Light impurities are sucked away by the
Cleaned grains are discharged through the
The cyclone separator is used extensively in
processing and other operations as a device
for collecting end product.
It is also frequently used in connection with
pneumatic conveying of products
and wastes from processing. These are used
for removal of particle about 10 μm or more
in diameter from the air stream.
These are used for separating particle from
liquid droplets from gases.
Cyclones are basically used for cleaning air
or for settling the dust particles etc.
It is used in combination with some other
machines e.g. as you have seen with
hammer mill/aspirating column etc.
The aspirating column is the equipment
which is used for this purpose.
The material is fed from the duct provided at
The lighter particles have less terminal
velocity whereas grains and other heavy
particles have more value of terminal
This difference in terminal velocity provides
the basis for the separation of materials.
This is best suited for removing very small
sized and immature grains from healthy
The separations by inclined belts draper takes place
due to difference in shape and surface texture of the
This technique of separation is used when all other
The mixture to be separated is fed over the centre of
an inclined draper belt moving direction.
The round and smooth grains roll or slide down the
draper at faster rate than the upward motion of the
belt and these are discharged in a hopper.
The flat shape or rough surface particles are carried to
the top of the inclined draper and dropped off into
The belts of different degrees of roughness may be
used as a draper for separate materials.
Feed rate, speed of draper and angle of inclination
are other factors for effective separation of dissimilar
Electrostatic beneficiation allows for separations based
on differences in surface chemistry (work function) or
In some instances, these separations would not be
possible using size or density separations alone.
Electrostatic separation systems operate on similar
principles. All electrostatic separation systems contain
a system to electrically charge the particles, an
externally generated electric field for the separation to
occur in, and a method of conveying particles into and
out the separation device.
In all electrostatic units, high potentials are used to
give practical forces of attraction. Since
electrostatic charges leak away rapidly in moist air, so
equipment & air must be dry.
Magnetic Separators are most commonly used to
separate iron or steel materials that have a low
Since magnetic separators have a wide variety of
functions, several devices are available.
A simple method is of keeping a magnet close to the
contaminated material as it passes along a conveyor.
The iron and steel particles are collected on the face
of magnet and removed periodically.
Another method is using a magnetic pulley in a belt
conveyor. The magnet will attract the iron or steel
particles and therefore deflected to one side
Magnetic separator performs separations on the basis
of surface texture and stickiness properties of the
Since the grains does not contain any free iron,
therefore are not attached by the magnet.