A possible configuration for the combined system proposed by Massachusetts Institute of Technology researchers.
[Image: Jeffrey Hanna/MIT.]

By Samantha James

RESEARCHERS at the Massachusetts Institute of Technology (MIT) have designed a hybrid system that could boost efficiency of coal-powered plants and simultaneously cut emissions in half.

The proposed hybrid system – designed by MIT doctoral student Katherine Ong and Professor Ahmed Ghoniem – could generate as much as twice the fuel-to-electricity efficiency of conventional coal-fired plants.  This would mean a 50 per cent reduction in carbon dioxide emissions for a given amount of power produced.

The concept, as described in a paper published in the Journal of Power Sources, combines coal gasification and fuel cells into a single system. The hybrid fuel cell would generate enough heat to sustain the gasification part of the process, eliminating the need for a separate heating system, which is usually provided by burning a portion of the coal. In the proposed system, coal gasification would make it much easier to carry out carbon capture and sequestration — capturing the output gas and burying it underground or disposing of it some other way — to eliminate or drastically reduce the greenhouse gas emissions.

The study demonstrated that using steam instead of carbon dioxide to react with the coal would produce two to three times the power output.
Ms Ong said that in comparison to conventional coal-burning power plants, which typically converted 30 per cent of the energy contained in the coal, the proposed combined gasification and fuel cell system could achieve up to 60 per cent efficiency. Following pilot-scale plant tests to measure the performance of the system in real-world conditions, a full-scale operational system could plausibly be built within “a few years” according to Ms Ong.

“This system requires no new technologies,” she said.  “It’s just a matter of coupling these existing technologies together well.”

Although initial outlay would be more expensive than existing plants, investment could be paid back within several years due to the system’s efficiency. Ms Ong said that given the importance of reducing emissions, the initial capital may be easy to justify, especially if new fees are attached to the carbon dioxide emitted by fossil fuels.

“If we’re going to cut down on carbon dioxide emissions in the near term, the only way to realistically do that is to increase the efficiency of our fossil fuel plants,” she said.