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Explosion Protection

Basic Guidelines to achieve reliable Explosion Protection

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...valuate the process possibly in coordination with the machine fabricator taking into consideration the dust's minimum ignition energy.

The following conditions have to be fulfilled for the determination of the avoidance of ignition sources as exclusive protection concept:

  • Development resp. collection of efficient ignition sources at the separated process has to be excluded.
  • It has do be 'normal flammable dust', i.e. the minimum ignition energy has to be > 10 mJ.
  • There must not be any hybrid mixture (composite consisting of explosive dusts and gases).

The danger of an ignition (according to the first point) can be reduced by a spark detection and extinguishing system in the piping or a spark eliminator in front of the filter.

Constructive Measures

If the above described measurements are not sufficient it is necessary to include constructive explosion protection measures. The predominantly used constructive measure are explosion relief by bursting panels, flameless explosion relief and explosion supression.

Explosion relief by bursting panels is the most cost-efficient constructive explosion protection measure. If the excess pressure of pstat of 0.1 bar is reached, the burst panels open and the explosion pressure and the flames are discharged into the open. The pressure in the filter housing increases up to the maximum explosion (over)pressure pred,max, which is 0.2 bar for the standard version.

The disadvantage of this protective measurement is the effect of the explosion in front of the burst panels. Therefore only a relief to the outside is allowed. A safety area in front of the burst panels is specified in which no one is permitted to stay during system operation.

Gallery

It is advantageous if the discharge takes place in an upward direction. This is possible, for example, with the PT-filter systems manufactured by Keller Lufttechnik, which have been especially designed for this type of application.

At an installation in a room or if the safety distances cannot be adhered to, it is necessary to use flameless de-pressurising units. There are systems in which the flames can be put out by an integrated flame filter. On the crude gas side, explosion-technical decoupling happens e.g. via a back pressure flap.

Explosion suppression offers another way to enable the installation in a work‑hall and in applications where toxic dusts can occur. With this solution, the explosion is prevented from happening at all by an early detection and quick addition of a dry powder, while the affected system is put to a halt.

If this solution is used, only a maximal reduced explosion overpressure of pred,max of 0.3 to 0.5 bar occurs, while the decoupling of the different system sections is done by a chemical barrier in the suction ductwork.

The protective systems described in this article provide examples of how de-dusting systems can be equipped with an explosion protection.

There are of course also other protection concepts, including, for example, designing a system in such a way that it is able to withstand the maximal explosion pressure. All of this concepts have been used successfully in various applications by Keller Lufttechnik, who dispose of the necessary know-how and experience. n

* U. Stolz, Keller Lufttechnik GmbH + Co. KG, Germany, Tel. +49 (0) 70 21 / 5 74 - 0, E-Mail: sz@kl-direkt.de

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