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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 duct system.

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

Dust Collection Applications

Paint Dip-Solvent Vapors

Plating Tank

Hood Enclose

Manifold Design-Distribution Types

Suspended Hoods

Push Pull Hoods

Pouring Station

Ducting System to transfer dusts form hoods to dust collectors

Dust Collector Types

Dust Explosions
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.

Engineering Data from Industrial Ventilation Handbook.



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