By Ben Schiller

"Fluid flows" don't figure much in discussions of renewable energy--but perhaps they should. Think of all the pressurized liquid in industrial processes: oil refining, chemical and food processing, water preparation. At the moment, much of the potential energy that is created when those liquids are pressurized is lost. And yet, a good amount of it can be recovered--either as part of the process itself, or "harvested" to make electricity.

You might be surprised how much of this is already happening. Energy Recovery, an equipment supplier in California, has been recycling energy in desalination plants for 20 years.

CEO Tom Rooney describes the company's hydrologic device as a three-foot long tube with a fast ceramic rotor inside. It acts "like a Gatling gun that fires high-speed water ... and in doing so, extracts the energy," he says.

In the desalination plant, huge pumps push seawater through a membrane, leaving about 40% of the fluid potable, and sending the rest back to the ocean. The device diverts "bullets" of energy from the briny flow to the original flow. Rooney says that reduces the energy needed for pumping by 60%.

Energy Recovery has installed 14,000 devices so far, on seven continents. That equates to about 12 billion kilowatt hours of energy being saved, or $1.2 billion, a year. Rooney says operators of the plants--whose electricity bills are huge--can make back their investment in three to six years (the devices last at least 25 years).

He sees opportunities in other industries, too, and with municipalities. "You have a very clumsy assortment of pressure up and pressure down throughout large municipal distribution systems. There's no question that there is an enormous opportunity to go in and harvest the pressure," he says.

It's also possible to generate electricity, if you don't want to reuse the energy in the water for something. We wrote about another company that's already doing that in New York.

Mining companies, for example, can generate electricity when they send down flows of water and product from high-up mines. "There is an incredible amount of money coming down off that mountainside," Rooney says. Energy Recovery's generators have 78% efficiency, compared to 98% for its diversion tubes.

"Ten years from now, people will look back and think how silly we were throwing away gigawatts of power, just because they happened to be in fluid flows."

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