Factors influencing dust collection equipment selection include:
* Concentration and particle size of contaminant.
In most dust conveying systems, usual dust range from 0.1 to 100 micron - a rather wide
range of particle sizes.
* Degree of collection required.
Evaluation will consider the need for high efficiency high cost equipment such as electrostatic precipirators; high efficiency moderate cost
equipment such as fabric or wet collector units; and the lower cost primary
units such as the dry centrifugal group. Degree of dust collection required can
depend on plant location; compariosn of quantities of material released to
atmoshere with different type of dust collectors; nature of contaminant - its
salvage value or its potential as a health hazard, public nuissance or ability
to damage property - and the requirements of the local or state air pollution
regulations.
* Characteristics of air or gas stream.
High temperature gas streams exceeding 180 F will prevent the use of standard cotton
media in fabric collectors; presence of steam or condensation of water vapor
will cause packling and plugging of air or dust packages in fabric and dry
centrifugal collectors. Chemical composition can attack fabric or metal in dry
collectors and cause extremely corrosive conditions when mixed with water in wet
type collectors.
* Characteristics of contaminant.
Chemical composition can cause attack on dust collector elements or corrosion in wet type
dust collectors. Sticky materials like metallic buffing dust impregnated with
buffing compounds can adhere to collector elements plugging dust collector
passages. Linty materials such as dust from textile opener Kole Calhoun Jersey , picker and napper will adhere to certain types of collector surfaces or elements. Abrasiveness of many materials in moderate to
heavy concentrations such as dust from sand blasting will cause rapid wear
particularly on dry type centrifugal collectors. Particles size and shape will
rule out certain collector designs. The parashute shape of particles such as
"bees wings" from grain will "float" through centrifugal collectors due to their
velocity of fall being slower than much smaller spherical particles of the same
specific gravity. Combustible nature of many finely divided materials will
influence selection of explosion proof dust collectors for such
products.
* Methods of disposal.
Methods of removal and disposal of collected materials will vary with the material, plant process, quantity
involved and the collector design. Dry collectors can be unloaded continuously
or in batches through dump gates Mike Trout Jersey , trickle valves and rotary locks to conveyors or containers. Wet collectors can be arranged for batch removal or continual
ejection of dewatered material by flight conveyors or draining as a slurry.
Material characteristics can influence other problems, such as packing and
bridging of dry materials in dust hoppers, floating of slurry forming
characteristics in wet collectors Justin Upton Jersey , etc.
One of the most efficient type of dust collectors is Electrostatic Precipitator.
The principle of dust collection relies on the ability to impart a negative charge to particles in the
gas stream causing them to move and adhere to the grounded or positively charged
collector plates. Most precipitators are made for horizontal air flow with
velocities 100 to 600 fpm. The collecting plates or electrodes are parallel
elements, usually on 9-inch centers, and constructed in various ways including
corrugated or perforated plates for rod curtains. The electrode rods are
centered between the collector plates. Volatge difference between electrode and
plate is 60 Zack Cozart Jersey ,000 to 75,000 volts in most designs. Collector plates of cylindrical shapes surrounding the electrode tod are provided where
water is used to wash off collected material and where the gas stream is under
high pressure or vacuum.
Removal of the collected material is obtained by rapping or vibrating the elements either continuously or at predetermined
intervals. Vibration or unloading usually takes place without stopping air flow
through the cleaning cycle.
Pressure drop is low. Collection efficiency is high and nearly uniform regardless of particle size including sub-micron
particles. Space is relatively large and cost is high where small gas volumed
(below 50,000 CFM) are involved due to the cost of high voltage electrical
equipment. Efficiency is improved with increased humidity of the air stream as a
change takes palce in the dielectric properties of the dust. Heavy
concentrations Albert Pujols Jersey , on the other hand, cause a reduction in collection as the space chatge on numerous particles blankets the corona effect from the
electrode.
Electrostatic precipitators have been extensively used in high temperature gas cleaning from equipment such as blast furnaces, open heart
furnaces and central station pulverized fuel boilers. The chemical industry has
many applications including sulfuric acids plants Nolan Ryan Jersey , carbon black, cement kilns and soda sh from paper mill black liquor furnaces. As voltage setting is close to the spark-over
potential, application is limited to materials that are not explosive or
combustible in nature unless the carrier gas stream is an inert gas.
For additional information please refer to
http:olegsystemsairsystemIndex.
Oleg Chetchel
Industrial Air Process Engineer
Oleg Systems Co.
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