Dominant factors controlling the efficiency of two-phase flow cleaning in spiral-wound membrane elements

Two-phase flow cleaning has been successfully applied to control fouling in spiral wound membrane elements. This study focuses on its experimental optimization using a Taguchi Design of Experiment method (L-25 orthogonal arrays) to elucidate the influence of different factors and to reveal the important one(s) affecting the cleaning efficiency of two-phase flow cleaning. All possible combinations of the factors, i.e. feed type, spacer geometry, gas/liquid ratio, and liquid velocity, each at five levels were evaluated. The main effect of each factor on the efficiency of two-phase flow cleaning was measured by determining the performance response (mean of cleaning efficiency) and by calculating the mean signal-to-noise ratio. An analysis of variance was applied to calculate the relative contribution of each factor on the efficiency of two-phase flow cleaning. The results showed that the feed type is by far the most essential factor contributing to the cleaning efficiency. The spacer geometry is ranked second, followed by the gas/liquid ratio and the liquid velocity, which both have an only very minor effect on the cleaning performance. In terms of practical application, the operator should consider first the type of foulant prior to taking a decision on whether or not two-phase flow cleaning will be effective. Once the foulant type is defined, the use of the highest gas/liquid ratio, the highest liquid velocity, and the thickest feed spacer (diamond type) are recommended to achieve maximum two-phase flow cleaning efficiency.