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Borrowing from two different research areas that hes pursued over his career, Sandia researcher Rich Diver (6218) has invented a whole new way to make hydrogen to power automobiles and homes. His invention, the Counter Rotating Ring Receiver Reactor Recuperator (CR5, for short), splits water into hydrogen and oxygen, using a simple, two-step thermochemical process. The CR5 is a stack of rings made of a reactive ferrite material, consisting of iron oxide mixed with a metal oxide such as cobalt, magnesium, or nickel oxide. Concentrated solar heat is reflected through a small hole onto one side of the stack of rings. The side of the rings in the sunlit area is hot, while the other side is relatively cold. As the rotating rings pass each other in between these regions, the hot rings heat up the cooler rings, and the colder rings cool down the hot rings. This arrangement results in a conservation of heat entering the system, limiting the energy input required from the sunlight. Steam runs by the rings on the cooler side causing a chemical reaction to take place, allowing the ferrite material to grab oxygen out of the water, leaving the hydrogen. A separate chemical reaction that drives off the oxygen occurs where the sunlight directly illuminates the ferrite material at the solar receiving end. This is needed to regenerate the rings so they can react with more water during the next cycle. This is out-of-the-box thinking, says Rich, principal investigator of the internally funded Laboratory Directed Research and Development (LDRD) project. We are combining a mechanical engine with a chemical producing device something not done before to produce hydrogen. And its something that probably only Rich could have contrived because of his unique background. He has knowledge of splitting water using high-temperature solar techniques the theme of his PhD dissertation at the University of Minnesota and of concentrated solar gained from his 15 years working with Stirling engine solar collector systems at Sandia. Stirling dishes named after Robert Stirling who invented them in 1816 generate electricity by focusing the suns rays onto a receiver, which transmits the heat energy to an engine. The engine is a sealed system filled with hydrogen, and as the gas heats and cools, its pressure rises and falls. The change in pressure drives the pistons inside the engine, producing mechanical power. The mechanical power in turn drives a generator and makes electricity. The key to a Stirling engines high efficiency is heat recuperation, analogous to the CR5. Instead of making electricity like the Stirling systems, Richs invention will produce hydrogen. Rich envisions fields of large mirror dish collector systems making hydrogen, which would be stored and sent to stations where hydrogen-electric hybrid vehicles could fill up. He and co-collaborator Jim Miller (1815), a chemical engineer, have been testing materials at the University of New Mexicos Advanced Materials Laboratory to determine which will be best for attracting oxygen in the cool stage and releasing it in the hot stage. This invention calls for a new type of material, Rich says. We have to come up with one that is black and absorbs heat from the sun and which has the right oxidation reaction. Through the tests at the Advanced Materials Laboratory, Rich and Jim have shown that by suspending the ferrite material in zirconia, a refractory oxide that withstands high temperatures, there was a high yield of hydrogen quickly and repeatedly, even after forming the mixture into complex solid shapes. Without using the zirconia, the ferrite material doesnt hold together well; The ferrite/zirconia structures are laid line-by-line using robocasting, a method developed and perfected by other team members that relies on robotics for computer-controlled deposition of materials through a syringe. The materials flow like toothpaste and are deposited in thin sequential layers onto a base to build up complex shapes. A near-future step will be to build a prototype of the CR5, Rich says. Rather than constructing large dish mirrors to collect the concentrated solar, as is his ultimate goal, the initial tests will be done in an indoor solar furnace (see front-page photo) using a heliostat at the DOE-owned, Sandia-operated National Solar Thermal Test Facility. Rich says the problem he and Jim are attempting to solve is extremely difficult. The water molecule (in the steam) is a tough nut to crack, Rich says. We are putting different things together in ways other people havent thought of before. Its long-term stuff but ultimately can result in a clean alternative to pulling oil out of the ground.
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