All In One Boat

From the University of New Mexico comes an intriguing idea for desalinization. By placing two 30 foot tall cylinders near each other, one with salt water the other with fresh water, and a connecting pipe at the top, a small amount of heat applied to the salt water side will create enough of a vacuum at the top for vaporization to take place below the boiling point. The fresh condensate moves to the fresh water side replacing that drawn out at the bottom for irrigation, washing etc.

While clever, there are several problems. Keeping the water columns at the necessary height with shut off valves and intake valves can presumably be done automatically. The automation will have to be rugged and simple. 30 feet however, is fairly high, and likely not suitable except in rural areas. The amount of water, however, is not so insignificant. A 30 foot column with a 4 foot diameter can hold about 3,000 gallons of water. As I understand the scheme, the fresh water side has to be primed almost to the top, meaning the primer water has to be found or transported to the spot before the device works, perhaps not easy in water stricken areas. The article does not mention the evaporation rate possible, thus the gallons per hour transformed and the return on investment. Finally, there is the matter of the brine left on the saline side. How often does it have to be drained, and how? Where does the brackish water go — and at what cost to the environment? It will be interesting to see where UNM takes the idea.

The heat requirements are said to be so low that small solar, or even the exhaust from other household or industrial appliances, such as air conditioners, may be enough to create the vacuum.

Then for another approach to desalinization and energy usage there is the PX Pressure Exchanger which recaptures energy in the waste product, brine, of reverse osmosis.

State-of-the-art desalination plants suck in seawater and then use electricity-driven pumps to put it under pressure. This salty stream is then slammed against filters designed to let the fresh water bleed through while sequestering the high-pressure brine – a process called reverse osmosis.

“It takes a lot of pressure to get the pure water to go away from the salt, and it takes a lot of energy to pressurize the water,” Stover said.

That’s where Energy Recovery comes into play. The company designed its pump to capture the pressure trapped in that left-behind brine and recycle its energy into repressurizing the next batch of virgin seawater destined to be slammed against those reverse-osmotic filters.

Desal Pump