Sensitivity to explosion

Joachim Geisler

Conical star-pleated filter cartridges with a PTFE membrane have proven themselves even in critical applications, such as the separation of highly adherent particles (e .g. talc, icing sugar, cocoa powder, etc.). A better cleaning performance than cylindrical filter cartridges and more efficient flow ratios result in up to 30 % higher capacity. Compared to devices with filter hoses or filter bags, the advantages of Mahle dust collectors are obvious: lower investment costs due to the more compact design (minimal floor space), less energy loss owing to the lower flow rates and a longer cartridge service life as a result of reduced wear – all of which contribute to lower overall operating costs.

The efficient filtration technology implemented in both small and large Mahle filter units is based on efficient dust separation using high-quality filter media in combination with a cleaning system that is optimised for the filter cartridges. This is important in the case of critical fine dusts. The benefits of conical filter cartridges compared to their cylindrical counterparts cannot be overlooked:

Sensitivity in explosion protection does not stop at filter media that are capable of dissipating electrostatic charge. When dealing with powders in the food and chemical industries, electrostatic charge is not the only factor to be reckoned with; these powders are also highly flammable. To avoid hazardous spark discharges, all metal parts must be earthed. A conductive connection between the filter cartridge, panel and housing is essential; if not, the ‘condensation effect’ can result in high-energy discharges. All electrical components must therefore be designed with dust explosion protection. Without such protection, these sparks would cause detonations or even explosions, depending on the dust type and concentration, with the familiar devastating effects.

When designing an Atex filter system, it is essential to take explosive characteristics into account from the very beginning in addition to parameters such as dust fineness, bulk density, adhesion and agglomeration properties or moisture – failure to do so can lead to unpleasant surprises of both a technical and a financial nature. The most important characteristics are the ‘notorious’ minimum ignition energy of the combustible dust measured in the laboratory and the limit of 10 mJ or 3 mJ. Even close to this limit, sensitivity is vital, as an operating temperature just a few tenths of a degree above room temperature (minimum ignition energy) results in a considerably lower ignition energy in the application.

If this preventive explosion protection is no longer sufficient to guarantee the safety of the filter unit (for example, the minimum ignition energy), an explosion-proof (pressure burst-proof or pressure-resistant) design must be chosen. Thanks to this integrated explosion protection according to DIN EN 14460, the Mahle filter systems in the pressure burst-proof range satisfy even the most stringent requirements. The explosion protection concept includes components for pressure relief and isolation as well as a suitable control cabinet with features to improve plant safety.

The filter cake of a dust collector should not be cleaned with a jet pulse more often than necessary. On the one hand, this means that the maximum permissible differential pressure must not be exceeded, while on the other the cleaning interval should not be so short that a filter cake is unable to build up. An adequate filter cake acts as an auxiliary filter layer, providing additional retention.

Differential pressure controls (Atex-compliant for Zone 22) offer significant advantages:

Mahle Industriefiltration michaela.marquardt@mahle.com www.mahle-industriefiltration.com