Promising Bio-Gasification Technology Turns Coal to MethaneBy Engineering360 News Desk | March 29, 2016
Two researchers at Southern Illinois University are using biology to convert coal to methane, which burns cleanly and produces half the carbon dioxide emissions.
Yanna Liang, associate professor of civil and environmental engineering, and Satya Harpalani, professor of mining and mineral resources engineering, have found ways to fire up the microbes that eat coal and excrete methane. The methods could be applied to both the waste coal by-product left over from coal mining, as well as abandoned coal mines and played-out gas wells across the U.S.
Coal gasification is not a new concept, but it comes with barriers. “Gasification of coal is usually done using high temperatures,” Liang says. “That produces a big carbon footprint and takes a lot of energy to do.”
Instead, the duo are working on a process called “bio-gasification,” which transforms coal into methane biologically—"a very mild process that doesn’t generate as many environmental problems as combusting coal," says Liang.
The key to the researchers’ process lay in determining which of the tiny life forms that feast upon coal are best at excreting methane. To do so, Liang took samples of microbes found in the water surrounding the coal and conducted DNA sequencing to identify more than 200 bacterial species; then it was a matter of finding how to stimulate the microbial activities.
“Coal is a big molecule and some of the bacterial species can break it down into smaller molecules and then even smaller compounds like ascetic acid, carbon dioxide and volatile fatty acids,” Liang explains. “And from there, certain archaea species can convert those smaller molecules into methane.”
“You have these microbes, and they work together as a community to break down coal into methane,” she says. “It’s a natural process. But our purpose is to speed up the process to generate methane faster.”
To achieve this goal, the researchers fed different nutrients to the microbes to promote their growth. Depending on the situation, the process would call for adding certain microbes to a coal supply or simply encouraging what microbes are there by feeding them certain nutrients that encourage them to thrive—or a combination of both approaches.
There are several possible approaches the research might ultimately support. For instance, the microbes could be injected into an abandoned, flooded mine, where they could create harvestable methane supplies.
“When coal mines close, they typically leave about 50% of the coal in place,” Harpalani says. “Half of it is lying there with lots of wide spaces, like a chess board, in between. In some cases we could feed the nutrients to microbes we know are there and maintain methane production on the coal existing in situ.”
In the case of waste coal left on the surface, operators could build a silo to enclose the coal and inject the microbes into it. “The gas would bubble up and you would pipe it out, much the way an anaerobic digester works on a farm,” Harpalani says.
While Liang works on the microbe research, develops suitable nutrient recipes for different scenarios and optimizes the bio-gasification process to enhance methane yield, Harpalani analyzes the coal to look for changes in its composition and clues for improving the process.
Harpalani says the pair started on the concept in 2013 with a grant from the Illinois Clean Coal Institute that had the researchers looking mainly at using the process on waste coal that is often left in slurry ponds or piles on site at coal mines. Encouraging results prompted the two to apply for DOE grants, which allowed them to look at applying the process to coal still in the ground, such as in abandoned coal mines.
“If you think about it, we have trillions of tons of coal resource in the U.S., but 90% is unmineable,” Harpalani says. “It is either of poor quality or too deep, or the seam isn’t wide enough to justify building a mine. So instead of just leaving it there, this process would mean we can still get something out of it.”