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Electrostatic with regard to explosion safety

Notes on the evaluation and avoidance of electrostatic charges

Electrostatic charges can occur when two surfaces are rapidly separated, whereby at least one surface must be an insulator. Critical processes, for example, are pneumatic conveyors, Big Bag filling stations, or even silos with the danger of a conical pile discharge. In order to avoid electrostatic discharges at such FIBC filling stations, it is necessary to assess the bulk material and to select the proper FIBC Type. Type C Big Bag has conductive filaments, which allows grounding for safe filling / emptying. Such grounding can be carried out by means of a cable and clamp. Another option is the grounding by means of a grounding monitoring system such as FARADO fibc. An approval function enables the Big Bag Type C to only be filled if the grounding is correctly established.

Electrostatic charges during the filling of silos with a pneumatic filling

Another source of electrostatic charges is in places where a pneumatic transport or pneumatic filling of silos by trucks is carried out. If an explosive atmosphere develops outside the truck, and the truck charges up electrostatically due to the conveyance, there will be an acute risk of explosion. For this purpose, always ensure that the truck is properly grounded. The Farado I offers the possibility to perform resistance monitoring of the connected object in addition to the conventional grounding test. A release of subsequent processes thus takes place only if the object is within the defined capacity range. In addition to grounding the truck, care must also be taken to ensure that the conveying line is properly executed. Adequate means that this must be electrically conductive/conductive dissipating and grounded. Insulating intermediate pieces such as sight glasses or similar should be avoided, as these may lead to propagating brush discharging.

Conical pile discharge in silos

Bulk solids are generally not to be regarded as conductive, and are dangerously charged during the pneumatic conveying. If the silo is correspondingly large and the median of the bulk material is also larger in median, there is a risk that the cloud of dust above the bulk material will ignite due to a conical pile discharge. With the aid of the bulk material median and the silo diameter, the equivalent energy that can be generated by this discharge can be calculated. If, for example, the conical pile discharge cannot be excluded as an effective ignition source, a protection through protective systems must be established in case of doubt. Flameless explosion venting by means of a Q-Box, or explosion suppression by means of the Q-Bic offer numerous options for the indoor installation. The protection of adjoining plant components must also be taken into account during the protection design. Thus the supply line must be isolated against the pressure and flame of a possible explosion.

Details

  • Gallbergweg, 59929 Brilon, Germany
  • Alexander Kemmling