Hybrid system could clean up coal power

An artist's rendering of a possible hybrid system showing steam (pink arrows) passing through pulverized coal, and releasing gas which goes through a fuel cell at the top to create electricity(Credit: Jeffrey Hanna)

Even though 2015 saw the biggest decline in coal usage around the world on record according to Greenpeace, the use of the material is still thriving globally. In fact, according to the US Energy Information Administration, global coal consumption was at about eight billion short tons in 2012 (around 7.2 billion tonnes), the most recent year for which the agency provides statistics. So if coal isn't going away any time soon, what is there to do about the fuel source that is often blamed for pollution and global warming due to carbon emissions? Make it more efficient. And that's exactly what a new hybrid energy system out of MIT could do.

According to MIT News, conventional coal-burning power plants only convert 30 percent of the energy contained in coal to electricity. That's a pretty low efficiency rate. A new system that combines two existing technologies — coal gasification and fuel cells — could up that rate to between 55 and 60 percent, in effect halving the amount of carbon dioxide produced for producing the same amount of energy using today's methods.

Both of these methods are currently used to create energy in today's world, but stacking them together in one system could be the key to greater efficiency, says MIT doctoral student Katherine Ong and professor Ahmed Ghoniem, who reported their theory in the Journal of Power Sources.

The system would start with coal gassification, a process where coal is crushed to a powder and heated in a flow of hot steam that releases the gases it contains — primarily carbon monoxide and hydrogen.

After those gases are freed, Ong and Ghoniem suggest funneling them through a fuel cell where a membrane splits off the carbon monoxide and hydrogen from oxygen, thus creating electricity. Such fuel cells were announced in 2011 by a team from Geogia Tech. The fuel cell would, in turn, create heat that could generate more steam to continue the gasification process. This would eliminate the need to burn some of the coal to generate the higher temps at which gasification occur.

Because nothing is actually burned in this system, the researchers say that there would be less ash and other pollutants from a plant employing this method which, thus far, has only been tested using computer simulations. And while carbon dioxide would be a byproduct of the process, it wouldn't be mixed with air, as is the case in traditional factories, which would make it easier to capture and sequester.

To test out the real-world application of the hybrid theory, Ong says a small pilot plant should be built which, she adds, could happen relatively quickly. "This system requires no new technologies," she says. "It's just a matter of coupling these existing technologies together well."

Late last year a process that uses algae and the coal dust usually wasted from mining operations to produce burnable bricks was created by researchers at the Nelson Mandela Metropolitan University (NMMU) in South Africa. That process, along with with MIT's hybrid system, could certainly help coal shake off its reputation as a dirty fuel source and help the world get more efficient power from the material for years to come.

Source: MIT News

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