EQUIPMENT
FOR SCREENING
SCREENING:
Screening
is a method of separating particles according to size alone.
Under
size: fines pass through the screen openings
Oversize:
tails do not pass
A
single screen can make but a single separation into two fractions.
These are called unsized fractions, because although either the upper
or lower limit of the particle sizes they contain is known, the other
limit is unknown. Material passed through a series of screens of
different sizes is separated into sized fractions, i.e. fractions in
which both the maximum and minimum particle sizes are known.
SCREENING
EQUIPMENT:
Cutting
diameter Dpc:
It
marks the point of separation; usually Dpc is
chosen to be the mesh opening of the screen.
Actual
screens do not give a perfect separation about the cutting diameter.
The under size can contain certain amount of material coarser
than Dpc,
and the oversize can contain certain amount of material that is
smaller than Dpc.[1]
INDUSTRIAL
STRAINERS:
Some
of industrial strainers available are simplex basket strainer, duplex
basket strainer, and Y strainer. Simple basket strainer is used to
protect valuable or sensitive equipment in a system that is meant to
be shut down temporarily. Some commonly used strainers are bell mouth
strainers, foot valve strainers, basket strainers etc.
Fig.
1: Industrial Basket strainers
SIEVES:
A sieve,
or sifter,
is a device for separating wanted elements from unwanted material or
for characterizing the particle size distribution of a sample,
typically using a woven screen such as a mesh or net. The word "sift"
derives from 'sieve'. In cooking, a sifter is used to separate and
break up clumps in dry ingredients such as flour, as well as to
aerate and combine them. A strainer is
a form of sieve used to separate solids from liquid.
Fig.2:
sieves or sifters
ANALYTICAL
SIEVE SHAKERS:
A device used to shake a stacked column of standard sieve-test trays to cause solids to sift progressively from the top
(large openings) to the bottom (small openings and a final pan), according to particle size.
Fig.3 Analytical Sieve
Shaker
STATIONARY AND ROTARY
SCREENS:
Rotating
and stationary screens for automatic and efficient removal of coarse
solids process streams and waste water effluent. Screens can be used
anywhere in your plant, but are most often used as a pre-screen to
further waste water treatment.
Screens
Provide Great Value:
Screens
provide great value in their ability to handle a wide range of
flow-rates and solids loading. They work well on granular, fibrous,
greasy or sticky solids. We also provide equipment for further de
watering of the screened solids.
The
right screen can reduce water usage, improve the efficiency of final
waste water treatment, reduce maintenance, recover products, reduce
hauling costs and improve processes. Contact us for assistance with
your screening application.
Fig.4:
Rotary Screen
Screen
Applications:
Process
water
Waste
water
Pulp
and paper mill effluent
Wood
room effluent
Stock
thickening
Broke
thickening
Rejects
thickening Save all
Poultry
plant wash water
Primary
feather and offal waste water
Peeler
effluent
Solids
recovery
Coolants
Fig. 5: Stationary Screen
GYRATORY or VIBRATORY
SCREEN:
Boxlike machine with a series of horizontal screens nested in a vertical stack with downward-decreasing mesh-opening
sizes; near-circular motion causes undersized material to sift down through
each screen in succession.
Or
Gyratory
Screens, used in mechanical screening and sieving is based on a
circular motion of the machine. Unlike other methods, gyratory screen
operates in a gentler manner and is more suited to handle fragile
products, enabling it to produce finer products. This method is
applicable for both wet and dry screening.
A
distinct difference to other techniques is that the gyratory motion
applied here depends on eccentric weights instead of vibrations,
which can be varied based on individual process
requirement.
Gyratory equipment contains decks of screens on
top of each other with the coarsest screen on top and the finest
below. The feed is inserted from the top and gyratory motion triggers
the penetration of particles into the next deck through screen
openings.
Casings
are inclined at relatively low angles (< 15°) to the
horizontal plane, with gyrations occurring in the vertical plane. The
eccentric masses can be varied in such as the increase of top
eccentric mass leads to an increase in horizontal throw, promoting
the discharge of oversize materials. Increment in bottom eccentric
mass boosts the material turn over on the screen surface, maximizing
the quantity of under-size-material penetration. Over size
materials are discharged via tangential outlet.
Fig.5:
Gyratory Screens-Schematic diagram
CENTRIFUGAL
SITTERS or SCREEN SCROLL CENTRIFUGE:
Screen
scroll centrifuge is a filtering or screen centrifuge which
is also known as worm screen or conveyor discharge centrifuge. This
centrifuge was first introduced in the midst of 19th century. After
developing new technologies over the decades, it is now one of the
widely used processes in many industries for the separation of
crystalline, granular or fibrous materials from a solid-liquid
mixture. Also, this process is considered to dry the solid material.
This process has been some of the most frequently seen within,
especially, coal
preparation industry.
Moreover, it can be found in other industries such as chemical,
environmental, food and other mining fields.
Fig.6:
Screen Scroll Centrifuge
[4]
http://en.wikipedia.org/wiki/Screen_scroll_centrifuge
