In a nondescript site in Midland, Texas, an inexpensive new process is cleaning up some of the most contaminated water around—the extremely salty stuff that comes up with oil at wells. By the end of next month the technology is expected to be chugging 500,000 gallons per day, furnishing water that’s sufficiently clean to use in hydraulic fracturing, or fracking, for oil and natural gas production (see “Natural Gas Changes the Energy Map”).
The technology may provide a way to deal with the increasing amounts of contaminated water the fossil fuel industry is generating as it pursues more and more difficult-to-reach deposits. Many oil formations can produce as much as five barrels of contaminated water for every one barrel of oil. And the volume of this so-called “produced” water is rising as the industry pumps water into nearly depleted wells to enhance oil recovery.
In the Midland plant, the technology is proving more economical than the existing strategy: re-injecting the wastewater back into the wells, while purchasing clean water for use in nearby fracking operations. Right now, gas producers tend to store water that comes back up during the process in man-made ponds and dilute it for reuse. Ultimately they inject the dirty water deep underground for final disposal.
“This is far and away the largest such plant anyone has ever built. Past prototypes have done 200 gallons a day; this is vastly larger, modular, and scalable; if they wanted to double it, they could,” says John Lienhard, a professor of mechanical engineering at MIT who heads MIT’s Center for Clean Water and Clean Energy, where the technology was developed.
The new plant uses technology from Gradiant, an MIT spinout company based in Woburn, MA. The water is pretreated to remove oil and grease residue and solid particles. The company heats the saline water and sprays it into a porous material with a large surface area, saturating air with water vapor.
This water-saturated air is then pumped up through tiny holes in a series of shallow, water-filled trays. As bubbles pass through the water in the trays, the water vapor in the bubbles condenses and joins the water it is passing through, creating more fresh water. This so-called “bubble column” allows the company to condense water vapor without needing expensive metal heat exchangers.
The process—which the company calls carrier gas extraction—recycles up to 85 percent of the heat needed to keep the system running. The remaining waste is then disposed as sludge in landfills. The project is being done with Pioneer Natural Resources, an oil company in Texas.
Anurag Bajpayee, president and CEO of Gradiant who co-developed the technology with the company’s CTO, Prakash Govindan, says the initial focus is on the booming petroleum and natural gas industry in the United States and elsewhere. “Water issues have been a point of a lot of controversy for the industry,” he says.
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