Influence of feed moisture on the efficiency of dynamic air classifiers
M.Sc. Gunnar Kretschmar1, Dr.-Ing. Thomas Mütze2, Frank van der Meer3
Knauf Gips KG, Am Bahnhof 7, 97346 Iphofen, Germany, Kretschmar.Gunnar@knauf.de
2
TU Bergakademie Freiberg, Institute of Mechanical Process Engineering and Mineral Processing,
Agricolastraße 1, 09599 Freiberg, Germany, thomas.muetze@mvtat.tu-freiberg.de
3
WEIR Minerals, Egtenrayseweg 9, 5928 PH Venlo (The Netherlands), F.vanderMeer@weirminerals.com
1
ABSTRACT
The air classification of moist bulk materials is addressed in the literature insufficiently. Therefore a feasibility study investigated the influence of feed moisture on the separation efficiency expecting a reduction
with higher moisture content in the feed. Two iron ore samples were characterized in terms of the nature
of bonding of moisture as well as its effect on the agglomerate strength. The classification tests themselves
were conducted with two dynamic laboratory air classifiers at cut sizes from 45 to 110 µm and a moisture
of the feed material between 0 to 10 wt.-%. The quality of classification was assessed by split factor, cut
size, separation efficiency, moisture of both products, as well as the yield of the fines as product fraction in
a corresponding processing plant. An initial approach was found for a technological implementation: A
sufficient drying of a moist feed can be realized simultaneously to the pneumatic transport inside the classifiers. In the present case the drying effect and dispersion intensity was sufficient to provide good separation results up to 3 wt.-% feed moisture. An additional drying step was necessary beyond 3 wt.-%.
KEYWORDS
moist feeds, air classification, separation efficiency