Low Pressure Desalination
The system utilizes the natural effects of gravity and atmospheric pressure to create a vacuum in which water can evaporate and condense at near-ambient temperatures. Two 30-foot vertical tubes — one rising from a tank of saline water and the other from a tank of pure water — are connected by a horizontal tube. The barometric pressure of the tall water columns creates a vacuum in the headspace.
At normal temperatures, Khandan said, evaporation from the pure-water side will travel to the saline side and condense as the system seeks equilibrium. “That’s nature,” he said. “We want it to go the other way.”
Raising the temperature of the water in the headspace over the saline column slightly more than that of the freshwater column causes the flow to go in the other direction, so that pure, distilled water collects on one side and the brine concentrate is left behind in a separate container. A temperature increase of only 10 to 15 degrees is needed, Khandan said.
“That’s the trick of this vacuum,” he said. “We don’t have to boil the water like normal distillation, so you can use low-grade heat like solar energy or waste heat from a diesel engine or some other source of waste heat.”Low Pressure Desalination