Mechanisms of Scale Formation and the Influence of Antiscalants thereon

Abstract:
Scale formation is one of the major limiting factors in most desalination processes. To suppress scale formation in waters with a high concentration of sparingly soluble salts, such as calcium carbonate or calcium sulphate, antiscalants are added to the pre‐treated water before the actual desalination in the reverse osmosis modules. Even though large efforts have been spent, most theoretical explanations for the effectiveness of antiscalants are based on thermodynamic equilibrium approaches and lack any valuable predictive character. Recent works in our group have shown that scale formation is dominated by a variety of kinetic effects on different size levels. One of the challenges in predicting scaling behaviour of a reverse osmosis system arises from the partly self inducing character of the kinetics and the high number of recirculations in desalination process. The process does not only depend on the operation conditions, but also very strongly on the starting conditions and thus on the inner state of the feed solution, which is hardly known in the necessary detail. Even though the presented model does not allow for quantitative prediction, it still creates an impression of the physical process and helps to decide if the applied quantitative shortcut method is a conservative or courageous guess.

Keywords:
antiscalants, crystallisation

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