Explosion Venting of filters for single- and multi-spot de-dusting

Bag filters, filters with cartridges and electrostatic precipitators for de-dusting purposes, in which the sucked in dust could create an explosive atmosphere, have, if not protected by other means, to be protected by constructional explosion protection.

If equipped with explosion vents, the pressure shock resistance of the filter construction has to comply with the applicable standards. These standards demand a pressure shock resistance slightly above p_red. The value p_red expresses the highest possible value vent-mitigated deflagration pressure may reach. The interdependency of the mitigated deflagration pressure and the explosion venting system’s sizing and effectiveness is reflected by the equations for the calculation of vent area (vent sizing) requirements the norms provide.

In case of dust explosion scenarios in which a fire could be the consequence of the deflagration occurrence, it is recommendable to install self reclosing explosion vents, in order to avoid possible ingress of air oxygen via the open venting orifices.

In practise, wrong explosion venting arrangements can often be found.

E. g. explosion vents positioned in front of filtration elements, in configurations that hinder the venting.

Often, the recoil (reaction) forces and the flame length of an exiting blast are not taken into account correctly.

Deflagration-induced pressure is only slightly mitigated, before it affects the clean air compartment(s) of the filter. As a result, under certain conditions, the penthouse covers could be thrown off and the fan on the clean air side damaged.

Even more important is the fact that flames and pressure may affect the suction spots via the dirty side connections.

These connections have to be equipped with an adequate explosion isolation system.

A simple although in this case adequate form of explosion isolation is the installation of a so called explosion diverter. In case the filter had self reclosing explosion vents, this explosion diverter would also have to have the self reclosing feature, in order not to spoil the effect.