MVR is used to raise the pressure and temperature of vapor. The vapor is drawn out of the evaporator and compressed before being returned to the evaporator and compressed before being returned to the evaporator when mechanical compression is used. The pressure increase takes place by means of mechanical energy, used to drive the compressor. No thermal energy is supplied to the evaporator (except steam for heating in the 1st effect). There is no excess steam which has to be condensed. Apart from the steam used for start up, a MVR evaporator requires no steam and no cooling water. However, if high concentration to be achieved, it is advantageous to use a steam heated finisher for the last concentration. In this way, it will be easier to control the evaporator. An MVR evaporator may also be coupled with TVR and/or multiple effect evaporation stages.
The high initial capital cost of an MVR unit must be weighed against the operating cost savings.