Navy

Low-energy desalination system

Water purification system utilizing naturally occurring ocean temperature gradients

Environmental

At present, approximately 1% of the world’s population is dependent on desalinated water to meet daily needs, but the UN expects that 14% of the world’s population will encounter water scarcity by 2025. Purifying ocean water into drinking water has not been economically viable for multiple reasons. One major reason is the enormous quantities of energy required to boil and condense water.

A novel invention from Navy researchers utilizes naturally occurring thermal gradients in the ocean to transfer needed energy to and from the water. In this way, the ocean is used as the heat source and heat sink for evaporating non-potable (saline) water under vacuum pressures and for the condensation of potable water. This saves significant cost of having to input all the necessary energy from manmade sources.

The system design includes a vacuum chamber above a body of water. The evaporation chamber holds a column of water at a sufficient height (33 ft. above the water line as the maximum height of an unsupported column of water under vacuum pressure is approximately 33 ft.) so as to create a low-pressure area above the column of water. Due to the low-pressure at the surface, the ambient temperature of the held water is sufficient to vaporize water at an upper surface of the column. A gas transfer tube is coupled to the first chamber so as to convey the vaporized water away from the first chamber. A second vacuum chamber is coupled to the gas transfer tube and receives the vaporized water. A condensation system is positioned within the second chamber receiving ocean water as well as a condensation collection system positioned to capture condensed water. Limited energy is used to transfer heat to the evaporation chamber and to pump down the vacuum chambers. A system to remove potable water from the evacuated condensing chamber is required.

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