The United States has enough space in its deep saline aquifers to safely store at least a century's worth of carbon dioxide emissions from the nation's coal-fired power plants, according to a new study by MIT researchers.
The study didn't tackle the next obvious question -- does it make financial sense to store such gases? Instead, it focused on whether there was enough space underground to even bother. The MIT team's analysis was published this week in the Proceedings of the National Academy of Sciences.
Coal-burning power plants account for about 40 percent of worldwide carbon emissions. Despite the development of clean energy and the emergence of natural gas, coal will continue to be a go-to power source because it's cheap and widely available. Carbon capture and storage, a system that can grab emissions then compress and store the waste in deep geological formations, has been proposed and pursued for years. Deep saline aquifers -- those more than half a mile under the surface and far below freshwater sources -- are considered one of the more promising places to store the gas. But until now, estimates of their capacity have ranged widely from a few years worth of coal-plant emissions to many thousands of years worth.
The MIT team created a model using tiny glass beads (as pictured above) to simulate how liquefied carbon dioxide would percolate through salty water in the pores of deep rock formations. The model had to capture the essential physics of the problem and be simple enough that it could be applied to the entire country, according to Michael Szulczewski, a graduate student who worked on the project as part of his doctoral thesis work.
That required the team to look at the details of trapping mechanisms in the porous rock at a scale of microns and then apply that to formations that span hundreds of miles. The study made a key conclusion that the rate of injection of CO2 into a reservoir is critical in making storage estimates.
Here's the basics of it all. Liquefied carbon dioxide naturally sinks when it's dissolved in salty water. "Once the carbon dioxide is dissolved, you've won the game" because the denser mixture would almost certainly never escape back into the atmosphere, Ruben Juanes, the ARCO associate professor in Energy Studies in the Department of Civil said in an MIT news release, . Check out this MIT video on the study.