After several years of promising research into efficient, Brayton-cycle turbines for power generation, scientists at Sandia National Laboratories are close to beginning the conceptual design phase for a 10 megawatt demonstration plant.The lab has been in discussions with potential industry partners for the scale-up project, and Sandia manager Gary Rochau said he expects an announcement “any day.” Once agreements are finalized, the rough timeline calls for a year of design before construction begins, then operational testing by year three. If concepts demonstrated by the lab thus far hold up in the larger plant, they offer the potential to greatly improve the efficiency of electrical generation from a range of power sources, including small modular reactors.“The big advantage is the efficiency,” Rochau told nuclearstreet.com. While performance depends on operating temperatures and other factors, the technology may offer a thermal-to-electric conversion efficiency 50 percent greater than comparable steam turbines. Generators with Brayton-cycle turbines, which function in a manner similar to jet engines, also require significantly smaller turbo machinery compared to the Rankine-cycle steam turbines used in existing nuclear plants. “We look at it as being one-tenth of the cost of a conventional steam system,” Rochau said.Other concepts explored by the Sandia team offer the potential for reactors with dry heat rejection, which could reduce the need for cooling towers and large nearby water sources. Other systems modeled for waste heat extraction after shutdown could possibly provide backup power in the event of a station blackout.Sandia’s research into Brayton-cycle turbines has been funded through a number of diverse Department of Energy programs over the years. Among them, the agency’s program for advanced SMR research and development will fund the study of heat rejection concepts that could be incorporated into reactor designs.To further experiments and data collection in a number of areas related to its supercritical CO2 Brayton cycle concept, the lab jointly developed a 250-300 kilowatt prototype with Barber-Nichols that Rochau said was delivered to the lab on April 24. It is nearly reassembled and will soon begin experiments as a user facility, allowing lab researchers and companies to move the technology toward commercial application. So far, Rochau said the primary interest has come from the gas industry for its potential for better waste heat recovery and bottoming cycles. He said the user facility’s first commercial client is expecting data by the beginning of October.The envisioned 10 megawatt plant hosted by Sandia would bring Brayton-cycle turbine generators even closer to commercial production. Rochau said cost estimates run between $30 million and $50 million, with natural gas as the heat source and a high-temperature oil as the likely working fluid coupled to the supercritical CO2 of the Brayton cycle. Demonstrating the Brayton-cycle concept on a commercial scale while continuing research into working fluids, heat exchangers, bearings, seals, materials and other design elements should eventually provide power plant designers of all stripes the knowledge base to potentially take advantage of a technology that can turn heat into power much more efficiently than with Rankine turbines. “We’re trying to get it at a level of maturity that the SMR vendors can say, ‘this is an alternative to doing this with steam,’” Rochau said. “I just love the fact that I’m not boiling water any more.”
Download the April 2011 presentation, Supercritical CO2 Brayton Cycle - Program Summary and Development Roadmap (6 MB .pdf)
The Brayton cycle was first tested (successfully) in 2002, in South Africa, by a composite team of Potschestrom University, the PBMR and IST, it was supposed to power the 169 Megawatts PBMR Reactor in South Africa. rgarr
PBMR used helium as a working fluid. Closed Braytons were 1st successfully tested in Switzerland in the late 1930's, see Hans Ulrich Frutschi's book, " Closed-Cycle Gas Turbines" for a good history overview.