Calcium sulphate scale prevention in a desalination unit using the SMCEC technique

The desalination unit UTAIM using the solar multiple condensation evaporation cycle principle (SMCEC) is confronted with the problem of heat-exchange surface plugging by dihydrate calcium sulphate. The aim of this work is the prevention of this scale problem by using chemical inhibitors. The kinetics of calcium sulphate nucleation and crystalline growth increase with temperature. At all operating temperatures, the solution keeps a large metastable domain. The supersaturation coefficient β at the end of precipitation is about of 2.5. In presence of increasing quantities of chemical inhibitors (RPI 2000, Flocon 260, STPP, Permatreat), the precipitation kinetics decrease. The RPI 2000 (polyacrylate) sharply inhibits the formation of sulphate scale at high and low temperature.

The chemical analysis showed that the brackish water of the desalination unit of Sfax has a high Scale Inhibition, % 30°C 70°C 50°C 90°C Inhibitor concentration, ppm Fig. 6. Effect of additive concentration on scale inhibition.