INDUSTRIAL VENTILATION DUST COLLECTION SYSTEM DESIGN
Modern industrial processes produce significant quantities of
airborne pollutants in all forms -- particulate, gases, vapors,
fumes and mists. Many are toxic and concentrations often exceed
safe levels of exposure. Reducing the pollutants to acceptable
levels is critical for the safe operation of many industrial processes
and mandatory to meet stringent emission regulations.
If high air velocities and a large pressure drop per 100 feet
of duct are allowed, ducts can be sized relatively small. But
excessive noise and a large total pressure drop necessitating
a powerful and noisy fan are almost certain results of downsized
Still, velocity constraints can be varied for individual duct
sections so that duct sizes can be selectively minimized without
adversely affecting noise considerations. Likewise, the maximum
allowable pressure drop per 100 feet of duct can sometimes be
increased when it is known that the resulting greater pressure
loss is still within the capacity of the fan.
Except for differences in desired velocities and pressure drops,
all of the above would seem to apply to industrial ventilation
and exhaust duct systems. This is not so for several reasons.
Industrial ventilation systems routinely utilize components rarely
seen in hvac duct systems such as hoods, dust collectors, blast
gates, and other such items.
These unique components not only require special consideration
in calculating their pressure loss, they also greatly influence
the design of the duct system. For example, a hood usually has
slots through which particulate or gases are drawn through. For
the hood to work properly, the connecting ductwork must allow
sufficient velocity (typically 3,500-4,500 fpm) so that the particulate
stays in suspension of the transporting air.
The dust collector of a ventilation/exhaust system not only contributes
a large pressure loss, it can also vary the density of the air
stream if it is a wet collector where moisture is added. Density
changes at the collector thus affect the pressure loss calculations
through all subsequent duct work.
Dust Colleciton System Main Components
Dust Collection Hoods
Ducting System to transfer dusts form hoods to dust collectors
Dust Collector Types
A dust explosion is very similar to a gas or vapour cloud explosion,
i.e. when a volume of a flammable mixture is ignited, resulting
in a rapid pressure increase and fire moving through the cloud.
A dust explosion occurs when a combustible material is dispersed
in the air forming a flammable cloud and a flame propagates through
it. This of course also depends on the supply of oxygen to the
fire, and the concentration of the fuel, if either of these are
in too high or low then the explosion will not occur.