Jont Allen reaching towards a technological Holy Grail: low-cost desalination of seawater

10/1/2021

Jenny Applequist, Coordinated Science Lab

“Water, water, everywhere, but not a drop to drink!” Those words were written to capture the horror of sailors on a becalmed ship, drifting helplessly on a ocean of salt water—but some fear they will increasingly apply to much of humanity. With the world’s population creeping towards 8 billion, disputes over access to scarce freshwater resources are already a major factor in human conflict around the globe.

Many techniques exist for “desalination” of salt water—removal of the mineral components that make salt water undrinkable, and unusable for agriculture—so why, on a planet that’s mostly covered with water, is water still such a desperately limited resource? The fact is that centuries of attempts have failed to find a method for desalination that doesn’t consume so much energy as to be cost-prohibitive in most situations.

Jont AllenIf CSL’s Jont Allen is successful, that might be about to change.

Several years ago, Allen—who is a professor in Electrical & Computer Engineering; Speech & Hearing Science; Nuclear, Plasma, & Radiological Engineering; and the Neuroscience Program—grew concerned about the threat posed by climate change. “I decided that I needed to do something about it,” he says. “My career has been all over the place, and this didn’t seem any different from many of the other really difficult tasks I’ve worked on.”

He eventually realized that a green technology for desalination, if applied on a grand scale, could not only lower the carbon content of the world’s oceans enough to offset climate change, but also produce a wonderful byproduct: enormous amounts of fresh water. “And that’s actually just as important,” he says. “You could argue it’s more important.”

He decided the goal was to figure out how to use thermal energy to power desalination: more specifically, he wanted to use direct sunlight as the primary, or even the sole, energy source. Over the past few months, with the help of Mechanical Engineering students in the ME 470 Senior Design Project course, he’s built some prototype systems and begun a series of experiments whose initial results have offered encouragement.

A drawing of Allen's proposed desalination platform
A drawing of Allen's proposed desalination platform. Credit: Lane Allen, AIA, LEED AP BD&C, Allen+Pepa Architects.

Allen’s ultimate vision is of a gigantic aquifer in the form of an elevated platform covered by an insulating thermal pane, which would admit sunlight. The aquifer would be close enough to the ocean that insulated pipes could conduct cold deep-ocean water up to the platform. As the cold water flowed across the platform, it would heat up under the sun’s rays and be partially converted to water vapor—which would consist of pure, salt-free water. The water vapor would then be drawn into an enclosed channel on the underside of the platform. Within that channel, it would be blown back towards the ocean, so that it would return to the input end of the system, directly underneath still-cold seawater just arriving from the ocean.

Allen’s key assertion is that there, by means of heat exchange, the vapor would condense; and in doing so, it would heat the water above, because the cooling of the water vapor would release latent heat. His idea is that the incoming seawater would be heated twice, both by the sun and by the heat released by the condensation process. Finally, the condensed vapor would drain out of the system as salt-free fresh water.

Allen is confident of eventual success, but stresses that he has yet to achieve a proof of the concept. He believes that his proposed solution resembles natural processes closely enough that it’s bound to work, once an appropriately tuned artificial system is developed. That’s the core challenge, in his view: while it’s essentially “Nature’s solution,” there’s a big catch—“We’ve got to bottle it!”