Fouling and Cleaning of Modified Stainless Steel Plate Heat Exchangers Processing Milk Products

Fouling of heat exchangers in dairy industries is still quite a severe problem both technically and economically. Altering the surface properties of the heating surfaces would be a way of solving this issue. Modified steel surfaces were tested in an Alfa Laval V2 plate heat exchanger throughout dairy product sterilization. The behavior was analyzed for 8 different surface treatments, such as coatings (Diamond Like Carbon [DLC], Silica, SiOX, Ni-P-PTFE, Excalibur®, Xylan®) and ion implantation (SiF+, MoS2). All fouling and cleaning experiments were carried out in standard and well-controlled operating conditions. After fouling, no significant difference could be seen between all the modified steels and the reference by statistical variance analysis. Cleaning efficiency of Ni-PPTFE appeared significantly the best. It could be suggested that the free surface energy plays a predominant role and the roughness a minor role in the level of fouling and cleaning efficiency

A study of CaCO3 scale formation and inhibition in RO and NF membrane processes

The formation of CaCO3 deposits on RO and NF membranes was investigated in connection with permeate flux decline. Experiments, in the presence and absence of scale inhibitors, were carried out in a cross-flow membrane test cell in order to examine the extent of metastable region without scaling and the scale characteristics. Three types of flat sheet membranes (LPRO and NF) were used in the experiments. In the absence of inhibitors, scaling (as determined by observing scale crystals on the membrane surface in SEM micrographs) occurred at supersaturation ratio at the membrane surface higher than approximately 4 (or LSIm > 1). These experiments show that partial coverage of the membrane by scale does not necessarily result in a proportional flux decline. Furthermore, it appears that the type of membrane affects the dominant CaCO3 polymorph formed on the membrane surface. Experiments with several commercial inhibitors were carried out, at a supersaturation ratio at the membrane surface of 9.8 (or LSIm similar to 2), most of them with an inhibitor dose of 5 mg L-1. All inhibitors (but one) performed well, i.e. no significant flux decline was observed during these tests. However, SEM observations on dried membrane samples revealed that, for three inhibitors, a thin layer of sludge-type deposits was formed, totally covering the membrane surface. (C) 2007 Elsevier B.V. All rights reserved

Modified stainless steel surfaces targeted to reduce fouling - surface characterization

The surface properties of several modified stainless steel samples were characterized according to their chemical composition, roughness, topography and wettability. The modifications tested were SiF3+ and MoS22+ ion implantation; diamond-like carbon (DLC) sputtering: DLC. DLC-Si-O and SiOx, plasma enhanced chemical vapor deposition (PECVD); autocatalytic Ni-P-PTFE and silica coating. X-ray photoelectron spectroscopy (XPS) and X-ray microanalysis were applied to determine the surface chemical composition. Atomic force microscopy (AFM) and stylus-type instruments were used for roughness determination, and the surface topography was imaged with AFM and scanning electron microscopy (SEM). The contact angle and surface tension were measured with the Wilhelmy plate method and the sessile drop method. For thick modified layers, only the elements of the coating were detected at the surface, whereas for thin layers the surface composition determined was that of the stainless steel substrate. The roughness of the 2R (cold rolled and annealed in a protective atmosphere) Surfaces was not altered by the modification techniques (except for the Ni-P-PTFE coating), while for the 2B (cold rolled. heat treated, pickled and skinpassed) surfaces an increase in roughness was observed. The silica coating produced surfaces with consistent roughness, independent of which steel substrate was used. DLC sputtering and Ni-P-PTFE coating produced surfaces with the highest roughness. All modified surfaces revealed a similar surface topography with the exception of the Ni-P-PTFE coating, for which the coating masked the underlying steel topography. In terms of wettability, the SiOx-plasmaCVD and NiP-PTFE coating, techniques produced the most hydrophilic and hydrophobic surfaces, respectively. (C) 2003 Elsevier Ltd. All rights reserved