Höflinger, W. (2022). PM 2.5 Separation Efficiency and Energy Assessment for Cleanable Oil-Water Soluble Mist-and Dust Filter Media. In Proceedings for the WFC13 (pp. 1–11).
In context of increasing energy prices and the goal of reducing CO2 emissions, the energy
consumption related to air filters has become the focus of attention. The filter medium is relatively the
most expensive part of a filter apparatus, especially if fine PM2.5 particles are to be separated. To
improve to choice of finding out suitable filtermedia for separation tasks, standardized tests for
classification of filter media are in use, whereby in addition to the separation efficiency the energy
consumption should be included. Depth filter media have already suitable test standards, EUROVENT
4/21-2019, EN779:2012, EN ISO 16890:2017 [1-3]. In case of cleanable filter media there are still
much work to do. Cleanable dust filter media work with alternating filtration and regeneration cycles,
where the filtration behavior changes from the very beginning over time until nearly a stationary state
is reached. In addition to the cleanable dust filter media, also oil-water soluble coolant mist filters can
be referred as cleanable filters. In this case the drainage flow of liquid out of the filter medium, which
partly discharges the separated and coalesced liquid droplets, would be the comparable cleaning effect.
The stationary stage is reached when the drainage flow, which increases with time, becomes nearly
equal to the in-going droplet mass flow. An analysis together with the cleanable dust filters turns out
further, that a common consideration can be advantageous to get solutions for existing tasks and
problems. In this paper will be shown how a PM2.5 quality factor QFPM2.5, which includes the energy
consumption (in case of cleanable dust filter media consisting of filter medium pressure drop and
cleaning energy), as well as the separation efficiency, can be used as a quality assessment parameter
for cleanable filter media. Tests on a VDI 3926 [4] cleanable dust filter test rig showed, that if the
cleaning energy is included in the energy part of QF, not the same quality factors were produced, as
when only the filter pressure drop alone was taken into account for the energy part. These
investigations were done with a series of 10 different cleanable filter media, which then results in
different quality ranking lists among them. The conclusion is, that the cleaning energy should be
implemented in the filter media classification. Further investigations showed, that dependent which
particle fraction is on the focus of separation (eg: fine, PM2,5 or less fine, PM10) different QF-values
results, which can also lead to a change of the filter media selection. A standardized assessment of
cleanable filter media is usually carried out during a stationary operation state, which is reached after
an aging period. The relevant standard for cleanable dust filter media is the VDI 3926:2004 guide line,
respectively ISO 11057:2011 [4]. For oil-water coolant mist filter media a new standard (ONORM
Z1263:2021 [5]) was developed. It includes also an aging procedure. Due to the Austrian legal limit
values for coolant mist emissions, the measurement of the separation efficiency focuses only on the
oily part of the oil- water mixed droplets, which cannot be evaluated by a sole droplet size
measurement. Details of this new measurement device (Cycle-FID [8]) will be described. Further the
filter test rig includes a special oil-water droplet generator, which ensures reproducible, enough high
oil-water droplet concentrations, usually found in real machining processes. Several tests with a series
of different oil-water soluble coolant mist filter media were conducted by this test setup and the PM2.5
quality factor QFPM2,5 is used to make a filter media ranking within this series.
