Untitled

The efficiency of cross-flow microfiltration processes is limited by membrane fouling and concentration polarization leading to permeate flux decline during operation. The objective of this study was to investigate the influence of static turbulence promoter on permeate flux during skim milk microfiltration and the potential application of this arrangement for an industrial development. Experimental investigations were performed on 100 nm ceramic membrane using the Kenics static mixer as a turbulence promoter. The insertion of the Kenics static mixer caused improvement of permeate flux of more than 700% at the same feed flow rate. Although the hydraulic dissipated power was significantly increased (about 6 times), the decrease of more than 25% in specific energy consumption was obtained by the use of the static mixer. Moreover, the presence of the static mixer in the membrane tube provided the similar permeate flux values at about 5 times lower cross-flow velocity, thus reducing the energy consumption for more than 80%. Additional energy saving was achieved using the Kenics static mixer with the aspect ratio (ratio of element length to mixer diameter) greater than 1, especially at the volumetric concentration factors greater than 2.

The experimental results clearly show that the improved performance of skim milk cross-flow microfiltration can be obtained by using the Kenics static mixer as a static turbulence promoter. The use of the Kenics static mixer results in the formation of a helical component of the flow, which enhances radial mixing and creation of secondary flows. Beside this, left- and right-hand alternations of helices cause the creation of vortex which additionally increases the shear rate at the membrane surface. This increased wall shear rate reduces the concentration polarization and the thickness of the membrane surface layer, leading to a large improvement of the permeate flux.