The Vision Sequester carbon dioxide in six-mile-long sausage-shaped plastic bags on the seafloor
The Plan It’s a hard sell. Cover thousands of square miles of ocean bottom with polymer-skinned sausage links 650 feet in diameter, fill them with carbon dioxide sucked from power plants, and leave them there for all eternity. “I thought the project was silly until I started to talk to marine engineers and do the math,” says physicist David Keith, a director at the University of Calgary’s Institute for Sustainable Energy, Environment and Economy. But by the time he finished a concept study on the project with engineers at Argonne National Laboratory and the University of Singapore, he was convinced that it was not only possible; it was downright practical.
“The basic physics is simple,” Keith explains. At ocean depths below two miles, liquid carbon dioxide is denser than seawater, so it sinks. In fact, for decades, scientists have suggested injecting liquid CO2 into depressions in the deep ocean so that they form lakes, an option that environmentalists have resisted because some of this CO2 would eventually dissolve and acidify the water. But contain that liquid in a corrosion-resistant material, like an organic polymer or titanium, and it could sit, safely, on the seafloor for several thousand years.
As for installation, the sausage skin is flexible, so engineers can roll each bag around a floating reel and then use a tugboat to tow it about 60 miles offshore. As the reel unwinds, the membrane sinks nearly two miles to the seafloor, where deep-sea rovers connect one end of each bag to valves along a main pipeline. After power plants capture CO2 emissions and compress the gas into liquid, a pipeline pumps two tons per second into the bags, which slowly inflate from their deepest end first. Since real estate is not a factor—the ocean covers 70 percent of Earth’s surface, and the necessary depths are reachable within 60 miles of most continental coasts—the pipeline can be continuously extended to accommodate new bags.
Potential Uh-Ohs Did we mention the vast quantities of CO2 that humankind currently dumps? It’s about 800 tons a second, enough to fill an oil tanker with CO2 every minute. To reduce current global emissions by even 20 percent, we would need to fill one bag every 11 days. Then there’s the problem of durability. What if a shark sinks its teeth into a bag, for instance, or the material falls apart? There’s no way to be certain that the bags won’t disintegrate after hundreds of years instead of thousands, as predicted.
ETA Keith says CO2 bags could be in place by 2020, pending regulatory hurdles.
—Rena Marie Pacella
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.