Study on inhibitors' performance under the condition of high concentration ratio in MED system

Abstract Improving the concentration ratio to reduce the emission of concentrated brine is required in some desalination plants. However, scaling problem will be aggravated with higher concentration. In this study, scaling tendency was analyzed according to two indexes including the Langelier Saturation Index and the Ryznar Stability Index. Four kinds of inhibitors were analyzed. Their inhibition performance under the condition of high concentration ratio in MED system was studied by both static jar tests and experiments on a small-scale falling film evaporation apparatus. Results indicate that severe scaling problems would occur when high concentration ratio encounters high temperature. Under the experimental condition, for which the temperature was 70 °C and the concentration ratio was 2.5, the alkaline scales were calcium carbonate. No magnesium hydroxide was formed. Calcium sulfate began to appear and increase when the concentration ratio exceeded 2. All inhibitors showed controlling effect on scale formation. Inhibitor A with its main constituents of HPAA and polymaleic acid showed the best inhibition performance. Better inhibition performance was achieved with higher inhibitor dosage, but no obvious improvement was observed when inhibitor dosage exceeded 5.5 ppm. The present study is helpful to the MED system under the condition of high concentration ratio.