Tornado in a Tube
In order to capture carbon dioxide from a power plant's smokestack, the greenhouse gas needs to be separated from the other flue gases. Typically, carbon dioxide makes up anywhere from 2 percent to 70 percent of the flue exhaust. To separate the gas, INEEL researchers are investigating an old technology in a new way -- the vortex tube.
Used for separating gases based on the size of their molecules, a vortex tube spins gas at a high centrifugal force -- this causes gases to move at different speeds through the tube. "The vortex is sort of like a tornado in a tube. It's a unique beast," says chemical engineer Kevin Raterman, one of two INEEL researchers attempting to improve the tube for this application.
Raterman and his colleagues at INEEL, Purdue University and several industrial companies are trying to improve the efficiency of a vortex tube by at least 50 percent and make the process more cost efficient. They'll experiment first with a natural gas stream, which usually contains about 8 percent carbon dioxide, and then adapt the system to the exhaust streams you might find on a power plant.
"We need a pressurized gas stream, so it makes sense to start with natural gas since it's already pressurized," said Raterman. They're hoping to develop a prototype carbon dioxide separator by the end of their three-year, $750,000 grant. By mixing liquid in with the gas in the vortex, they expect a large jump in the efficiency of the separation. Making the gas travel through liquid will separate the gas molecules more efficiently than through the air typically found in a vortex tube.