Investigation of the particle separation characteristics in the submicron and nanoscale size range for cake-forming surface filter media in gas cleaning applications

Current industrial dust emission limits and emission characterization in filter testing standards for cleanable surface filters are based on gravimetric (non-size-resolved) measurements. However, submicron and nanoscale particles often dominate emissions in terms of particle number concentration. This study provides a comprehensive analysis of the fractional separation efficiency and its evolution during dust cake formation over the full emission-relevant size range. Experiments were conducted in a filter test rig for cleanable filter media (VDI 3926 / DIN ISO 11057). Because particle penetration decreases rapidly as the dust cake is formed, a suitable experimental methodology was developed. Fractional separation efficiency was measured using submicron test aerosols (dried NaCl and high-purity water) that do not contribute to cake formation or enhance filtration characteristics. Between these measurements, a separate phase using coarse test dust (Pural SB) enabled controlled cake formation, while concentration decay on the clean-gas side was monitored. Aerosol measurements covered a wide range from approximately 10 nm to 10 μm using a combination of light-scattering aerosol spectrometer, condensation particle counter, and scanning mobility particle sizer. ... mehrThe filter medium itself had a most penetrating particle size (MPPS) of 305 nm with an efficiency of 53.3% and an upper separation limit near 4 μm. Even small increases in differential pressure (e.g. from 100 Pa to 200 Pa) shifted the emission-relevant range completely into the submicron particle size range. At 500 Pa, efficiency reached 99.8% at a MPPS of 126 nm. The results demonstrate the particle-size dependent filtration kinetics and the mitigation potential of surface filters considering potential (ultra-) fine particle emissions.