Dust Collection Q&A
You bring up some good questions on industrial ventilation. It is difficult to answer with simple answers because there are many variables that can affect the hood design. Some of the variables that could affect the hood design are distance from the source, weight off material, cross drafts, size of hood, accessibility around hood, bag disposal, etc. It seems to be that you have two different application dump stations and weighing hoods. Both applications will require the hoods to be located behind the station, in front of the worker. This will draw the fresh air around the worker while dirty air is pulled away from the worker.
The dump station can have two different styles of dust collectors, bag dump with integral dust collector or source capture with ductwork going to a central dust collector. If there are only a few dump stations in the plant, then most companies will use a bag dump with integral dust collector. A bag dump with integral dust collector is a self-contained dust collector mounted to a dump station and the dust will be pulsed off the filter back into the process. As a general rule the hoods should be enclosed (having top and side walls) with a design of 200-500 FPM (feet per minute). When there are multiple stations, a central dust collector is used. Usually, a major source of dust will be generated from the bag (garbage) after the material is dumped out. Extra source capture could be required.
The weighing hood stations will have ductwork going to a central dust collector, because there is not a place for the dust to drop back into the process. A general number to use is 50 cu ft/min/sq ft (cubic feet per minute/square foot) based on opening of the hood. It would be best to have a local dust collector vendor to examine our process to suggest the correct type of dust collector.
Each situation is different depending on the discharge velocity, proximity to structures that will cause turbulence, change in velocity and direction of the air flow. It is important to insure that there are no “hot spots” in terms of flow velocities and changes in velocity as well as direction in the booth.
It is therefore never a bad idea to control flow velocities (ducting sizes at the discharge) and flow directions (baffles, vanes, flow directors) to create the motion of the air that is desired for the paint booth.