Is a New Hybrid System the Cure for Coal Power’s Ills?

Researchers at the Massachusetts Institute of Technology (MIT) have combined two proven technologies to create a new hybrid system that could produce electricity, using coal as a fuel source, at nearly double the efficiency of conventional coal-fired power plants.

The concept-proposed by MIT doctoral student Katherine Ong and Ronald C. Crane (1972) Professor Ahmed Ghoniem-combines coal gasification and fuel cells to achieve efficiencies as high as 60%. Although the research used simulations rather than laboratory experiments, development of a pilot-scale plant may be the next step, which could validate performance in the real world.

According to an article, posted on the MIT News Office website, the researchers sought to combine the two systems because both operate at similar temperatures (800C or more). For that reason, the two components could exchange heat with minimal energy losses.

One advantage of the system is that no new technologies are needed to make it work; coal gasification and fuel cells are both widely used. But the researchers identified one big improvement over previous attempts-using steam to react with the coal particles. Most prior studies chose to use carbon dioxide for that step. However, Ong and Ghoniem demonstrated that the system produces two to three times the power output when steam is used instead.

The process involves passing steam through pulverized coal distributed on a grate near the bottom of a reactor vessel (Figure 1). This releases gaseous fuel made up of hydrogen and carbon monoxide. The gaseous fuel enters a solid-oxide fuel cell, where it reacts with oxygen from the air to produce electricity.

1. Proposed coal gasification/fuel cell hybrid. This image shows one possible hybrid system configuration. Steam (magenta arrows) passes through pulverized coal, releasing gases (red arrows), which react with oxygen (blue arrows) in a solid-oxide fuel cell (disks near top) to produce electricity (loop on right). Courtesy: MIT/Jeffrey Hanna

The hybrid system produces less ash and air pollutants than would be generated through combustion. Capturing carbon dioxide produced from the process is also easier because it is in a pure, uncontaminated stream, which is not the case in conventional coal-burning plants. Although a hybrid plant is expected to cost more to build than a conventional coal-fired plant, its improved efficiency and emissions benefits could make it a viable future option to help meet Clean Power Plan requirements.

-Aaron Larson, associate editor (@AaronL_Power, @POWERmagazine)

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