Avaliação do desempenho dos tratamentos das superfícies dos meios filtrantes submetidos à filtração por pulso de ar reverso
Abstract
The objective of this work was to characterize different fibrous filters after filtration
and to evaluate the surface treatment performance of these materials during pulse jet filtration,
in the removal of micrometric particles of dolomitic limestone. The filtration tests were
performed maintaining the filtration velocity constant at 4 cm/s. The operating parameters of
the cleaning media used were 200 ms and 2 kgf/cm2, corresponding to the cleaning pulse time
and pressure, respectively. The experimental results were: residual pressure drop, cycle time,
retained mass, cleaning and collection efficiency, particle deposition depth, deposited particle
size, deposited particle size, permeability, porosity, thickness, roughness and diameter of the
fibers of the filter media. Thus, in the comparison of fibrous filters of the same fiber
(polyester fiber), the results presented different performances during the filtration due to the
different surfaces, with untreated and treated (singeing/calendering and
calendering/thermofixation). Untreated surface filters showed higher cleaning efficiency,
lower residual pressure drop and increased permeability after fifty regenerations. However,
greater wear on the fibers was observed. The fibrous filters with surface untreated showed
close permeability values, lower cleaning efficiencies and higher residual pressure drop after
50 filter cycles. In addition, these fibrous filters with surface treated presented higher
collection efficiency after the filtration cycles, in relation to the fibrous filter untreated
surface. This indicates that the treatment on the surface of the filter medium is indispensable
for cycles with long duration using the pulse jet cleaning. In the comparison of polyester and
polypropylene fiber media subjected to the same treatment (calendering/thermofixation), the
results showed a high cleaning efficiency in the initial cycles, but a reduction of the cleaning
efficiency occurred with the increase of the filtration cycles. Furthermore, after the 100 filter
cycles, the polyester fiber media showed higher cleaning efficiency, higher collection
efficiency, lower particle retention (lower number and lower particle deposition depth), higher
permeability, lower residual pressure and lower mass retained after the pulse jet cleaning in
relation to PTFE immersion polypropylene media. It was also verified that, the polyester filter
media, collected more particles on the surface, characterizing a surface filtration and a lower
penetration of the dolomitic limestone particles in relation to the polypropylene fiber filter
medium. These results implied that the surface porosity of the filter medium interfered in the
formation and removal of the formed powder layer, helping or preventing the cleaning of the
filter medium. Thus, it was found that the polyester fiber filter media showed the best
operating performance with high collection and cleaning efficiency.