Can velocity and interstitial velocity are commonly confused when proper filter selection and baghouse sizing are being decided because they are very similar when filter bags extend to the hopper level. Can velocity is the vertical gas velocity throughout the housing, above the hopper level but before reaching the bottom of the bags. Interstitial velocity is the vertical gas velocity once the flow is at the bottom of the filter bags.
Interstitial velocity is higher due to the smaller cross-sectional area once the filter bags are considered. Having dead space under the bags provides low can velocity, essentially creating an internal dropout chamber that helps distribute and minimize horizontal particulate flows that can cause abrasion problems at the bottom of the bags.
Our experience shows that bag houses with bags some distance above the hopper have extended filter bag life and often calculations show that creating this low velocity zone is feasible and beneficial. One way to incorporate this idea is shortening the bag length. This proportionately reduces the filtration area and increases the air to cloth ratio. Something that is generally not considered because this specification is often misconstrued as the one and only bag house sizing parameter. When analyzing the total package; however, creating this dead space to provide a low can velocity proves to be an excellent way to increase bag life even with it slightly increasing air to cloth ratio.
In this Tip of the Month Video, IAC Product Manager Joe Haney explains the meaning of each term, and the impact both types of air flow have on capacity to meet production rates, dust collection efficacy, and ease of maintenance.
If you need to calculate interstitial velocity, or can velocity, for your baghouse or dust collector, visit our Baghouse Design Calculations page. You'll find interactive technical calculators for interstitial velocity, can velocity, filter cloth area, and air to cloth ratio.
To learn more, partner with IAC today because finding the best solutions for your particular questions is what we provide. IAC is your single source solution provider to ensure your baghouse is always operating at peak efficiency.