Basic Dust Collection Design, Part Two

This post is a continuation of our review of Basic Dust Collection Design. Our last post looked at part one, Assessing Your Dust & Sizing Ductwork.

Part Two: Selecting Your Dust Collector and Fan

The next step in your dust collection system design process is maintaining a consistent transport air velocity throughout the system. When conveying lighter or drier dust particles through the ductwork to the dust collector, a standard velocity may be sufficient. In the case of heavy or wet dust, a higher transport velocity will be needed to prevent settling or clogging. A dust collection system that is designed with multiple capture points will require branches in the ductwork for each point of capture. It will be necessary to size and locate transitions in the ductwork to assure that a consistent transport velocity is maintained throughout the branches. Minimum transport velocities typically range from 2000-4000 fpm.

For every point of capture, transition, branch and elbow in the ductwork, there will be a degree of resistance in the flow of air. The air resistance coefficient depends on the geometry of these areas. The total static pressure of the dust collection system is determined by considering the resistance coefficient for each area and the transport velocity. Total static pressure is one factor used to determine the proper size of the fan for the dust collection system.

In order to be effective, a dust collector must have adequate surface area of filters to capture the dust from the airstream. The collection efficiency of each filter goes down as more air is pushed through it. Only when an adequate air to cloth ratio is maintained will the dust collector be able to operate at peak efficiency, collecting more than 99.9% of dust particulate.

Air to cloth ratio refers to the ratio of air volume (ACFM) to total cloth area (sq. ft.) of the baghouse. This is derived by:

  1. Calculating the total cloth area of your collector by determining the total filter area of each filter
  2. Then taking the CFM of the system and dividing it by the total filter cloth area
  3. The resulting figure is the air to cloth ratio

Explosive dusts, sticky/oily/hygroscopic dusts, high temperature applications, and applications with high moisture content in the airstream are all dust collection applications that work best with the use of wet collectors, which we will cover in a future dust collection post.

If the task of getting all of the design criteria right for a dust collection system seems overwhelming, the experienced experts at G Squared are here to help. Contact us to discuss your project!

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