Dust is a term used to describe all airborne
particles – these can be wood, stone, flour, concrete, grain, mold or asbestos particles
as well as fumes and chemicals. Many activities create dust. Larger dust
particles get lodged in the nose and throat while the smaller more dangerous
particles get lodged deep in the lungs – these dust particles are the ones that
can cause fatal diseases. It is a legal requirement to assess and monitor the
dust risk in a work environment where the creation of dust is “part of the
job”. After the risk is assessed, dust extraction and suppression
equipment can then be installed and utilized. In order to lower your risk in
terms of dust exposure attempt to implement the following ideas – try to avoid
creating dust by investigating different ways of doing a dust-creating job; try
to prevent your exposure to dust or use dust extracting methods and equipment;
however, if it’s not possible to avoid dust completely, try to minimize your
exposure as much as possible. Remember, dust is dangerous – work safely.
A dust collector is a system used to enhance the
quality of air released from industrial and commercial processes by
collecting dust and other impurities from air or gas. Designed to
handle high-volume dust loads, a dust collector system consists of a blower,
dust filter, a filter-cleaning system, and a dust receptacle or dust removal
system. It is distinguished from air cleaners, which use disposable
filters to remove dust.
Five principal types of industrial dust collectors are:
·
Inertial separators
·
Fabric filters
·
Wet scrubbers
·
Electrostatic precipitators
·
Unit collectors
Dust collectors vary widely in design, operation,
effectiveness, space requirements, construction, and capital, operating, and
maintenance costs. Each type has advantages and disadvantages. However, the
selection of a dust collector should be based on the following general factors:
·
Dust concentration and particle size - For
minerals processing operations, the dust concentration can range from 0.1 to
5.0 grains (0.32 g) of dust per cubic feet of air (0.23 to
11.44 grams per standard cubic meter), and the particle size can vary from
0.5 to 100 µm.
·
Degree of dust collection required - The degree
of dust collection required depends on its potential as a health hazard or
public nuisance, the plant location, the allowable emission rate, the nature of
the dust, its salvage value, and so forth. The selection of a collector should
be based on the efficiency required and should consider the need for
high-efficiency, high-cost equipment, such as electrostatic precipitators;
high-efficiency, moderate-cost equipment, such as baghouses or wet scrubbers;
or lower cost, primary units, such as dry centrifugal collectors.
·
Characteristics of airstream - The
characteristics of the airstream can have a significant impact on collector
selection. For example, cotton fabric filters cannot be used where air
temperatures exceed 180°F (82°C). Also, condensation of steam or water vapor
can blind bags. Various chemicals can attach fabric or metal and cause
corrosion in wet scrubbers.
·
Characteristics of dust - Moderate to heavy
concentrations of many dusts (such as dust from silica sand or metal ores) can
be abrasive to dry centrifugal collectors. Hygroscopic material can blind bag
collectors. Sticky material can adhere to collector elements and plug passages.
Some particle sizes and shapes may rule out certain types of fabric collectors.
The combustible nature of many fine materials rules out the use of
electrostatic precipitators.
·
Methods of disposal - Methods of dust removal
and disposal vary with the material, plant process, volume, and type of
collector used. Collectors can unload continuously or in batches. Dry materials
can create secondary dust problems during unloading and disposal that do not
occur with wet collectors. Disposal of wet slurry or sludge can be an
additional material-handling problem; sewer or water pollution problems can
result if wastewater is not treated properly.
Dust collectors are used in many processes to either recover
valuable granular solid or powder from process streams, or to remove granular
solid pollutants from exhaust gases prior to venting to the atmosphere. Dust
collection is an online process for collecting any process-generated dust from
the source point on a continuous basis. Dust collectors may be of single unit
construction, or a collection of devices used to separate particulate matter
from the process air. They are often used as an air pollution control device to
maintain or improve air quality.
Dust collectors remove particulate matter in the form of
fine liquid droplets from the air. They are often used for the collection of
metal working fluids, and coolant or oil mists. Mist collectors are often used
to improve or maintain the quality of air in the workplace environment.
