Assessment of Metal Media Filters for Advanced Coal-Based Power Generation Applications Page: 4 of 21
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When the Pall FeAl filter media was cross-sectioned, a continuous melt-like iron oxide phase was seen
to have formed along the o.d. and i.d. surfaces of the filter wall, closing porosity, limiting direct passage
of the process gas through the filter media (Figure 5). Similarly, the open porosity through the filter
wall was reduced as a result of oxidation of the sinter bonded FeAl particles. An iron oxide (FeO)-
enriched phase formed along the outer surface of the contained particles. Subsequently FeAl2Ox and
FeAlO, were formed, surrounding the underlying particle core. Sulfur was detected to be present
within both iron aluminate-enriched layers. The central core of the residual FeAl particles was either a
densified structure consisting principally of the base metal iron, or an internally oxidized mottled
structure consisting principally of iron oxide.
USF FeCrAl (Hoskins 875 fibers: Fe, 22.5% Cr, 5.5% Al, 0.5% Si, 0.10% C). During the initial 242 hours
of operation in the 650 C (1200 F), simulated PFBC, process gas environment, an -0.1 pm thick
alumina-enriched phase formed along the outer surface of the sinter bonded FeCrAl fibers in the USF
filtration media. After 1,016 hours of operation in the 760 C (1400 F) simulated PFBC environment,
the thickness of the alumina-enriched layer increased to -0.2-0.5 pm. After 476 hours of operation in
the 840 C (1550 F) simulated PFBC process gas environment, a discontinuous -1-2 pm thick, alumina-
iron oxide-chromia layer formed along the outer surface of the FeCrAl fibers (Figure 6). Although
surface oxidation of the FeCrAl fibers occurred, the open porosity of the USF filtration media was
retained. During simulated PFBC testing, internal oxidation of the FeCrAl fibers was not observed.
Negligible oxidation resulted along the fibrous sinter bond interface.
Impact of Gas Phase Alkali. In contrast, the open porosity of the USF FeCrAl filter media was
limitedly retained after 225 hours of operation in the 840 C (1550 F), simulated PFBC, process gas
environment which contained both gas phase sulfur and alkali (Figure 7). Alumina-enriched, -2-3 pm,
needle-like whisker formations resulted along the outer surface of the FeCrAl fibers and FeCrAl
structural support mesh. Internal oxidation was not observed throughout the sinter bonded USF FeCrAl
fibers.
After 496 hours of operation in the 840 C (1550 F), simulated PFBC, process gas environment, the
microstructure of the USF FeCrAl fibrous filtration mat was no longer retained due to oxidation and
coalescence of the originally porous, fibrous, metal media. Gas flow permeability through the oxidized
filtration mat was severely restricted. Surface and subsurface void formations frequently resulted along
the periphery of the USF FeCrAl structural support mesh after 496 hours of operation in the gas phase
sulfur and alkali-containing, simulated PFBC, process gas environment. Limited sulfation was seen to
have resulted within chromia-enriched phases that were embedded within the coalesced USF FeCrAl
fibrous media.
USF Haynes 230 (57% Ni, 22% Cr, 14% W, 5% Co, 3% Fe, 0.1% C, 0.4% Si, 0.5% Mn, 0.02% La, 0.015% B,
2% Mo. 0.3% Al). The open porosity of the USF Haynes 230 was retained after 500 hours of operation in
the 650 C (1200 F), simulated PFBC, process gas environment (Figure 8). An -2.5-3.0 pm thick
oxygen-chromium-nickel-enriched layer formed along the surface of the sinter bonded Haynes 230
fibers. Internal oxidation of the fibers was initiated.
Oxidation similarly resulted along the outer surface of the sinter bonded Haynes 230 fibers in the USF
filtration media after 258 hours of operation in the 760 C (1400 F), simulated PFBC, process gas
environment. The open porosity of the filtration media appeared to have been retained during the initial
258 hours of exposure, but may have been limited after 524.5 and 1,016 hours of operation. With time,
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Alvin, Mary Ann. Assessment of Metal Media Filters for Advanced Coal-Based Power Generation Applications, article, September 19, 2002; United States. (https://digital.library.unt.edu/ark:/67531/metadc785343/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.