Evaluate several options for improving the overall safety of an existing dust collection system deflagration vent.
DUST COLLECTOR DEFLAGRATION VENT MODIFICATIONS EVALUATION
The client, an engineering company, was asked by the ultimate client, a specialty chemicals company, to design a system that would help protect plant personnel by mitigating the effect of a deflagration event from a dust collector. The dust collector is currently equipped with ductwork that is routed from the deflagration vent on the dust collector through the wall of the building housing the dust collector to an elevator waiting area frequented by personnel. The client asked Process Engineering Associates, LLC (PROCESS) to help evaluate the following three deflagration mitigation techniques to determine which one is best suited for this application: (1) rerouting the existing ductwork to a safer location, (2) installing a deflector plate, and/or (3) installing a deflagration shield.
PROCESS evaluated each of the proposed modifications in accordance with the 2007 edition of the National Fire Protection Association (NFPA) 68 Standard entitled Standard on Explosion Protection by Deflagration Venting. PROCESS and the client agreed that, at a minimum, a deflagration shield should be installed between the expected path of the deflagration fireball and the elevator waiting area. PROCESS calculated the expected length and width of the fireball based on the guidelines set forth in the NFPA 68 Standard in order to help define the required dimensions and location of the shield. PROCESS, however, did not attempt to define the load that may be applied to the deflagration shield by the sub-sonic pressure wave that would typically accompany the fireball during a deflagration event.
The remaining two mitigation techniques (deflector plate and ductwork modification) attempt to mitigate a deflagration by redirecting the fireball to a safer location, which inevitably increases the backpressure in the dust collector during the deflagration event. The NFPA 68 Standard, therefore, requires that the reduced pressure (PredPRED – i.e., the backpressure) in the dust collector be calculated when designing a deflector plate and/or adding (or modifying) deflagration vent ductwork. After completing this calculation, PROCESS discovered that the backpressure associated with the existing ductwork, without any ductwork modifications or addition of a deflector plate, was excessive and may cause the dust collector to overpressurize during a deflagration event. The maximum allowable working pressure (MAWP) of the dust collector was unknown at the time of the evaluation; PROCESS, therefore, recommended that the ultimate client determine the MAWP of the dust collector to ensure that it was higher than the calculated reduced pressure associated with the existing ductwork before performing any further evaluation of potential deflagration mitigation techniques.
- Specialty Chemicals Manufacturing
- Process safety systems evaluation