Neah uses large-scale Si process and targets military applications
- Publisher
- Elsevier Science
- Year
- 2006
- Tongue
- English
- Weight
- 96 KB
- Volume
- 2006
- Category
- Article
- ISSN
- 1464-2859
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✦ Synopsis
Tufts researchers develop breakthrough desulfurization technology
C hemical engineers at Tufts University in Massachusetts have found a way to continuously remove sulfur from incoming hydrogen before it is fed to solid oxide fuel cells. The work, published in the June 9 issue of Science, could be a significant step in making these high-temperature fuel cells more practical, since the sulfur in fossil fuels degrades the anode, reducing power production and eventually shutting down the fuel cell.
The Tufts group, led by chemist Maria Flytzani-Stephanopoulos, has designed the first sorbent system for high-temperature fuel cells. First, they use new materials: rare-earth oxides, known to be stable and able to absorb hydrogen sulfide at high temperatures. And, instead of filtering gas through a thick sorbent bed, they pass it over the surface of a thin sorbent layer. Flytzani-Stephanopoulos calls the new design a 'simple' solution to the sulfur problem.
For low-temperature (e.g. PEM) fuel cells the sulfur problem is addressed using a series of processing steps. Most of the sulfur is removed by refining the liquid fuel, and then using a reformer and sorbent materials. In the reformer, the fossil fuel is heated with air and water to make a hydrogen-rich reformate. The sorbents then soak up hydrogen sulfide, so that the gas reaching the fuel cell is sulfur-free. But common sorbents, such as zinc oxide, would degrade in high-temperature fuel cells, which operate at 600-1000°C.
According to a report in the MIT Technology Review, Lanny Schmidt, professor of chemical engineering and materials science at the University of Minnesota, says many operational issues have kept more powerful fuel cells off the market, including long startup times and parts wearing out under high temperatures. But he says that Flytzani-Stephanopoulos has 'an innovative, clever new way to remove sulfur'.
Rare-earth oxides are inexpensive and easy to obtain. The system could be added to an SOFC using two small boxes -one for fresh sorbents, the other for spent ones. Sulfur-free gases generated by the fuel cell would sweep the spent sorbents clean, allowing the same sorbents to be used repeatedly. There is no need for valves or pumps, says Flytzani-Stephanopoulos, because all gases would diffuse naturally through the system. She adds that her sorbents could also outperform those used for in low-temperature fuel cells.
The Tufts research is funded by the US Army Research Laboratory, which wants to use SOFCs as backup power for tanks and trucks. Since these vehicles run on fuel oil that is rich in sulfur, they would need effective sorbents.