October 1, 2017
Vent Size Verification for the XP Drum Kit
The XP Drum Kit is an innovative alternative to traditional rotary valves for providing a means of explosion isolation. The drum kit acts as a strengthened extension of the dust collector. It is designed to withstand the reduced pressure (Pred) that develops during a properly vented deflagration. As long as the explosion relief vent is sized properly and can accommodate the added volume of the drum kit, no modifications are required to the vent panel or isolation device on the inlet ducting.
Each drum kit adds roughly 8.7 ft3 (~0.25 m3) of additional volume to the dirty side of the collector. Though this additional volume is relatively small, it must be accounted for to ensure the entire explosion mitigation system to function as intended.
To illustrate the effect of this additional volume, consider a dust collector with a dirty side volume of 5 m3 and is rated to handle a reduced pressure (Pred) of 0.3 bar (~4.5 psi). The collector is servicing an operation that creates a very fine poly ethylene dust that has a KSt of 150 bar-m/s and a Pmax of 9 bar.
Per NFPA 68, Standard on Explosion Protection by Deflagration Venting, the minimum vent area required for this collector is 3.1 ft2. Let's assume that the collector is equipped with an 18" x 36" explosion relief panel that has a static burst pressure of 0.1 bar (~1.5 psi). This provides a vent area of 4.5 ft2 which is sufficient for handling combustible dusts with a KSt of 215 or lower.
The upper KSt limit is important to know because as we add the volume from the drum kit, the rating decreases. For example, if a XP Drum Kit is installed on this unit, the total volume increases to 5.25 m3. With the added volume, the upper KSt limit for this collector is now 207 bar-m/s.
For this application, the addition of the XP Drum Kit will work with no required modifications to the existing explosion mitigation system. This will be the case in many instances as the additional volume has a marginal impact on the upper limit of the KSt. However, it is important to factor in this volume when choosing the XP Drum Kit to ensure the existing or planned explosion relief device functions as intended.
XP Products can assist with the validation of explosion relief vent sizing. Please feel free to contact us for more information.
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