New Process May Hold The Key To 'Economically Viable' Desalination

By Neil A. McCarthy, BA, MSEd, middle school math teacher, South-Central Los Angeles parochial school

An energy-saving alternative to reverse osmosis (RO) desalination promises to reduce costs by more than 82 percent.

The sea, the blue sea – the phrase reminds one of the classic song, “La Mer”, written by Charles Trenet in 1946. It’s still blue, it composes 71 percent of the world’s surface, but alas it’s still full of salt. Desalination is a process that has been used with varying success for centuries; the problem is the cost of turning seawater into fresh water. Reverse osmosis (RO) has been the technology most favored by water suppliers and agencies because of its proven track record. However, RO is costly.

The Passarell Vapor Exchange System (P-VES) was designed as a highly efficient method of producing distilled water from saltwater. The simplicity of P-VES lies in its “single flash vapor” exchange. Seawater is raised to a vaporized state (steam) and pulled through differential pressures to an adjoining cell where, as it cools, the vapor recondenses to liquid as pure distillated water. A small amount of distillate, along with all the heavier-than-air particles (i.e., minerals/salts), is used to heat the next batch of incoming seawater. The P-VES is the only desalination process that recycles the thermal energy.