Multiple effect distillation using mechanical vapour compression

... or how MED can be applied without available vapour

Multiple effect distillation using mechanical vapour compression

The MED-MVC evaporator is a MED evaporator using only electrical energy. The evaporator itself is of the MED type and all the features described for the MED evaporator apply for MED-MVC process. This evaporator is equipped with a mechanical compressor. The compressor allows the vapour produced in the coldest effect to be brought to the pressure conditions prevailing inside the bundle of the first cell, thus enabling its latent heat to be re-available for distillation.

The input of energy ranges from around 18 kWh/m3 of distilled water for a single effect evaporator to around 8 kWh/m3 distillate water for a four-cell evaporator. This energy input being quite small, it is necessary to recover the heat from the distillate and the brine to preheat the sea water fed into the evaporator. This is done by means of two plate heat exchangers.

This process is attractive in terms of energy consumption. However, due to the cost of themechanical compressor, the investment cost is higher than for a MED or MED-TVC plant. This process is usually chosen for sites where the cost of energy is high.

From another point of view, due to its high efficiency, this process does not require any additional cooling other than the feed water. It makes it attractive in places where cooling sources are not available. The size of a MED-MVC plant is limited by the size of the compressors available on the market. For the time being, the maximum possible size would be evaporators producing around 5,000 m3 per day of distillate water.