Dynamic simulation of rinsing and regeneration networks based on high pressure RO

Abstract

The dynamic behavior of rinsing and regeneration networks (RRNs) has been investigated with emphasis on product quality assurance. RRNs allow recycling of discharged process bath liquor as well as a re-use of the purified rinsing water even at zero-water emission levels. However, during RRN start-up, inherent instabilities in the network might jeopardize the workpiece surface finish due to inconstant process bath composition, which is determined by the recycled concentrate, and insufficient final surface cleanliness. The objective of the present paper is to simulate start-up conditions and to analyse their effects on process stability. To implement these goals, a general dynamic model was developed on the basis of differential mass and material balances in combination with a constant-ratiomodel for high pressure reverse osmosis (RO). Additionally, a film theory expression was included into the latterto take into account the negative effect of concentration polarization near the membrane wall. In a case study, composed of an electroplating process comprising seven rinsing baths, an ion exchanger and a disc-tube RO module, it was shown that the final product quality is strongly influenced by start-up conditions. For the considered case, the quality prerequisites were achieved through starting up the regeneration units and the freshwater supply with anoptimal time delay of 8 % of the overall rinse water retention time.