Study on the performance of a scale inhibitor during horizontal-tube falling film evaporation of seawater

Abstract

Fouling on heat transfer surfaces is a severe problem and a complex phenomenon in multiple-effect distillation plants with horizontal tube falling film evaporators. In general, the scale on heat transfer surfaces is effectively prevented by adding scale inhibitors in large LT-MED seawater desalination plants. This paper presents an experimental study on the performance of a scale inhibitor with different seawater spray temperatures and salinities during falling film evaporation outside the horizontal tubes. The scale inhibitor is developed by the Institute of Water Treatment of Nanjing Tech University. Experiments are performed under the seawater temperature of 70°C, 80°C and 90°C and the salinity of 30g/kg, 60g/kg and 80g/kg. The dosage of the scale inhibitor is 6mg/L. The titanium tubes are used inside the evaporator and Dalian local seawater is selected as the working agent. The scale growing curves under different conditions are obtained through weighting the amount of the scale formed at different periods. The seawater temperature and salinity have a certain influence on the performance of the scale inhibitor during the horizontal-tube falling film evaporation. As the seawater spray temperature rises, the scale inhibition efficiency decreases. With the increase of salinity, the scale inhibition efficiency decreases.