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TECHNOLOGIES

Fig. 1 - Comparison of
temperature link and catalyst
lifetime for ESP vs. UCF vs.
Fabric Filter

Like the fabric (bag) filter, the ceramic filter has a
tube-like shape (candle) as shown in Fig. 2 and
works on the principle of barrier filtration. Howev-
er, in contrast to fabric filter material, the ceramic
fibers result in a rigid filter wall, which allows the
filter to build and maintain a residual layer, even
in times of pulse jet cleaning as shown in Fig. 3.

This special characteristic permanently moves
the barrier filtration zone into the filter cake, pre-
venting penetration of any dust constituents into
the filter wall. While this characteristic enables
reduction of PM and PM to >99.99% reduc-
2.5
10
tion levels, when catalytic filters are preferred,
it fully protects the catalyst against plugging or
Fig. 2 - Ceramic filter poisoning, which is finely dispersed on the ce-
candles of different length ramic fibers inside the filter wall. This ensures
minimal degradation of the catalyst for the full life
of the ceramic filter, significantly minimizing op-
erational costs associated with replacement or
regeneration of catalysts within traditional SCR
systems.

The catalyst formulation used within ceramic fil-
ters can be tailored to different functionality. Typ-
ical catalytic ceramic filters allow the control of
organic hazardous air pollutants (O-HAPs), typ-
ically from the BTX aromatics group (benzene,
toluene and xylene) and aldehydes, together
with dioxins and furans by catalytic oxidation.

When injecting ammonia or urea, the catalyst will
act like a typical SCR technology in controlling
NOx with a high efficiency, as shown in Fig. 4,
according to following chemical reactions:
NO + NO + 2 NH → N + 3 H O (fast)
2
3
2
2
4 NO + 4 NH +O → 4 N + 6 H O (slow)
2
2
2
3
6 NO + 8 NH → 7 N +12 H O (slow)
2 3 2 2
Fig. 3 - Principle of barrier The catalytic filtration process is completed with
filtration in the filter cake on addition of a dry sorbent for acid gas and aerosol
residual layer control. At elevated temperature hydrated lime
70 70 Impiantistica Italiana - Marzo-Aprile 2022