Influence of twisted tape turbulence promoter on fouling reduction in microfiltration of milk proteins
2011
Membrane filtration has become one of the major technologies in the food
industry. It is widely applied in the dairy industry, and it is mostly used
for the concentration and fractionation of milk proteins and for the whey
processing. Of all pressure driven membrane processes, ultrafiltration is the
most widely used. The major disadvantage of pressure driven membrane
processes is severe fouling of membrane during filtration particularly when
the fluids containing proteins are processed. Fouling with proteins is
complex phenomenon because it occurs at the membrane surface as well as in
the pores of membrane, and depends on the operating conditions and on the
interactions of proteins and membrane material. In order to reduce fouling of
the membrane different techniques have been developed, and one of them relies
on the changing of the hydrodynamic conditions in the membrane or module. In
this study, influence of twisted tape turbulence promoters on the fouling
reduction in cross-flow microfiltration of skim milk was investigated.
Twisted tapes with tree characteristic ratios of helix element length to the
tape diameter (aspect ratio) were studied. It was shown that twisted tapes
with different aspect ratios reduce fouling of membrane by a factor of three
or more. The presence of twisted tape induces changes in the flow patterns
from straight to helicoidally thus producing turbulence flow at the lower
cross-flow rates. Turbulence intensification prevents accumulation of
proteins at membrane surface enabling reduction in reversible fouling what
results in the reduction of overall membrane fouling. The best performance
was achieved using a twisted tape with the lowest aspect ratio of 1.0. This
promoter reduces fouling seven times at low transmembrane pressure and low
cross-flow velocity. The twisted tape with aspect ratio 1.0 induces the most
intensive turbulence, the longest helicoidal flow path, and appearance of
vortices near the membrane surfaces, so the scouring of proteins from the
membrane surface is the most intensive in that case.
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