Abstract
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.
Highlights
Eksperimentalna ispitivanja mikrofiltracije izvedena su na laboratorijskoj aparaturi za mikrofiltraciju/ultrafiltraciju sa cevnim membranskim modulom, u celosti izrađenoj od nerđajućeg čelika
This promoter reduces fouling seven times at low transmembrane pressure and low cross-flow velocity
Summary
Poslednjih 30 godina membranski procesi su postali jedna od najznačajnijih tehnika u prehrambenoj industriji, kao i u tehnologiji obrade vode [1]. Nesumnjivo, u prehrambenoj industriji, najveći broj membranskih procesa se primenjuje za koncentrisanje i frakcionisanje proteina mleka i preradu nusproizvoda kao što je surutka. Negativna karakteristika membranskih procesa uopšte, pa tako i onih primenjenih u industriji mleka jeste prljanje membrane tokom filtracije što rezultira značajnim opadanjem fluksa permeata. Negativna karakteristika promotora turbulencije jeste povećanje gradijenta pritiska duž membrane što je nepoželjno kod membranskih procesa sa pritiskom kao pogonskom silom, kao što je mikrofiltracija. Prednosti promotora u obliku uvrnute trake je u tome što obezbeđuju turbulentan tok uz znatno niži pad pritiska u odnosu na druge promotore kao što je zavrtanj ili keniks mikser. Imajući u vidu prethodno navedena rezultate, u ovom radu ispitivan je uticaja promotora u obliku uvrnute trake na prljanje membrane proteinima mleka sa ciljem povećanja efikasnosti procesa. Ispitan je uticaj uvrnutih traka različite karakteristične veličine (odnos dužine helikoidnog elementa i prečnika promotora) kao najznačajnijeg parametra koji odražava nivo intenziteta turbulencije
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