Experimental study of a three-effect plate evaporator: seawater tests in La Spezia

EasyMED, a new MED process constructed with plates has shown good performances for desalination of salted water in laboratory with only one effect [1]. In order to prove the reliability of this process in real conditions, a three effects evaporator was recently built in La Spezia Italy (see Fig. 1). This unit is composed of three effects in series and five cells in parallel and is heated by hot water at about 75 degrees C. 3 m(3)/d of high quality distillate with a conductivity lower than 20 mu S/cm was obtained. The evaporation ratio ranged between 8 and 13%. To avoid large consumption of energy to preheat seawater up to its boiling point, about 80% of the brine is recycled to the evaporator inlet. The overall heat transfer coefficients between heating water and seawater falling film reached 1400 W(.)m(-2.)K(-1) whereas the coefficient between condensing vapour and evaporating seawater is about 4000 W(.)m(.)2(.)K(-1). Temperature difference between the heating cells and the first evaporation cells is around 11 degrees C. For the rest of the unit, the temperature difference between condensation cells and evaporation cells of the next effect is between 3 and 6 degrees C. The first results concerning the influence of the heating fluid temperature and the heating fluid flowrate are presented.