Sandia researcher Rich Diver at a solar display.
Hydrogen Fuel at 2 Bucks a Gallon?
June / July 2006
Volume 4 Number 3
A novel combination of solar and chemical processes under development at Sandia National Laboratories may prove to be a source of hydrogen that lessens the nation's dependence on fossil fuels. Sandia mechanical engineer Rich Diver is working to perfect a technology he has dubbed Counter Rotating Ring Receiver Reactor Recuperator (CR5), which would use both the heat of the sun and oxidative properties of metals to break down the hydrogen-oxygen bonds in steam in a two-step process. Diver and his collaborators are working out design issues in anticipation of building a prototype reactor next year. Although Diver cautioned that much work needs to be done before such a technology could be commercialized, he conceded that in a best-case scenario the CR5 design could be producing hydrogen fuel at $2 to $3 per gallon in about five years. In commercialization, clusters of solar collection dishes would power CR5 reactors in much the same way that arrays of turbines today harness energy from the wind.
The CR5 reactor design currently consists of a series of metal ferrite rings. Each ring rotates in the opposite direction of its neighbors. Sunlight is concentrated through a small aperture to heat up one side of the CR5 reactor's rings on the edge. The sunlit side of the ring stack is kept hot, while the opposite side remains cooler as steam is introduced. Because the rings are rotating in alternate directions, they transfer heat from the hot portions of the rings to the cooler portions as the rings pass in the areas in between the two extremes. This significantly reduces the overall amount of solar energy needed to power the reactor.
The energized ferrite rings, which must be black to best absorb the solar energy, are able to chemically react with the steam to dissociate the water molecules. As the oxygen atoms are pulled into the rings, the hydrogen is bled off for compression and storage. When the rings return to the sunlit position, the solar energy causes the ferrite to give up its newly acquired oxygen, thus regenerating the rings for their next pass through the steam.
Although liquid water could theoretically be sprayed onto the rings, the researchers are designing the system to allow the water to turn to steam due to the high internal temperatures of the reactor. The physical state of the water will not enter into the thermodynamic equation, said Diver.
The major challenge of the reactor development is the composition of the rings themselves. Diver and chemical engineer collaborator Jim Miller are testing a variety of ferrite mixtures at the University of New Mexico's Advanced Materials Laboratory to determine which can most efficiently draw off the oxygen atoms.
Mixtures containing iron oxide plus either cobalt, magnesium, or nickel oxide have shown promise and Diver hinted that other combinations may hold even more potential.
The ultimate ferrite material will be suspended in zirconia. The researchers have noted that the refractory compound easily withstands the high temperatures generated by the CR5 system, and thus enables the most efficient breakdown of the water molecule. Without combination with zirconia, the ferrite reactivity decreases and the iron compound forms slag.
Zirconia also enables the ferrite compounds to be formed into complex structures, which facilitates the manufacture of the rings. Using a line-by-line computer-driven manufacturing technique called Robocasting that was developed by other members of the Sandia development team, the ferrite-zirconia structures are laid up by syringe in thin layers to form the complex shapes that will most efficiently grab the oxygen atoms.
Whether such a hydrolysis reaction can take place, explained Diver, is not so much the question as whether the reaction could take place fast enough to be commercially feasible. He and Miller are mulling whether a catalyst such as platinum could be used to speed the hydrolysis reaction without being expensively consumed in the process.
Diver, who earned his master's and doctorate degrees in mechanical engineering at the University of Minnesota, is coming at the issue of hydrogen generation through more than 30 years of experience in the breaking of water molecules through high-temperature solar methodologies. He has logged more than 15 years of experience working with Sandia's Stirling engine solar collector systems, which generate electricity by concentrating solar energy to heat hydrogen in a closed system. As the hydrogen heats and then cools, it creates pressure changes that power pistons in a manner somewhat analogous to an automobile engine. The energy of the moving pistons is then used to drive a generator that produces electricity.
That background in hydrogen thermodynamics made Diver the likely choice to head up a project at Sandia aimed at finding a novel way to produce economically feasible hydrogen fuel. "I was the go-to person for high-temperature thermal chemistry," said Diver, who now heads up the CR5 Laboratory Directed Research and Development (LDRD) project. The three-year project, which is being funded internally by LDRD, will move into prototype construction next year. Although the design ultimately would use large solar collection dishes, the prototype will make use of an indoor solar furnace owned by the Department of Energy and maintained at Sandia's National Solar Thermal Test Facility.
The advances made thus far on the CR5 project have drawn the attention of others within Sandia. "I'm delighted in the offers of support that we've gotten from research organizations here as word has gotten out about this project," Diver said.
G. Jeffrey Hoch reports on SNL for Innovation.
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