CSP power tower receiver systems during rapid transient weather periods can be vulnerable to thermal shock conditions from rain that which can facilitate the onset of leaks and failures that can have catastrophic consequences. Silicon carbide (SiC) materials have attractive receiver application characteristics for being light weight, having high-strength and excellent thermal shock resistance performance which make them a particularly good fit for receiver absorber materials in CSP. In this investigation, the performance characteristics of Ceramic Tubular Products (CTP) SiC ceramic matrix composite (CMC), multilayered tubes were explored with respect to thermal shock performance for solar receiver applications in next generation CSP plants. Here, thermal shock testing was performed at the Sandia National Laboratories (SNL) Solar Furnace facility using a dynamic stage and thermal shock tube test setup. The tubes tested under incident solar heat flux of 100 W/cm2 were heated with inner tube temperatures reaching approximately 800 °C, with outer temperatures exceeding or just reaching 1000 ℃ for the multilayer and monolithic SiC tubes respectively. The tubes were then quenched with simulated rain. The tubes were then cooled and subjected to hoop stress analysis using an Instron device to assess their subsequent mechanical strength. The on-sun study experimental results indicate an average of 24.2% and 97% higher hoop strength for the CMC tubes than those composed of monolithic SiC and aluminum oxide (Al2O3) respectively.
In order for Concentrating Solar Power plants (CSP) to achieve the desired cost breakpoint, significant improvement in performance is required resulting in the need to increase temperatures of fluid systems. A US DOE Small Business Voucher project was established at Sandia to explore the performance characteristics of Ceramic Tubular Products (CTP) silicon carbide TRIPLEX tubes in key categories relating to its performance as a solar receiver in next generation CSP plants. Along these lines, the following research tasks were completed : (1) Solar Spectrum Testing, (2) Corrosion Testing in Molten Chloride Salt, (3) Mechanical Shock Testing, and (4) Thermal Shock Testing. Through the completion of these four tasks, it has been found that the performance of CTP's material across all of these categories is promising, and merits further investigation beyond this initial investigation. Through 50 solar aging cycles, the CTP material exhibited excellent stability to high temperatures in air, exhibited at or above 0.95 absorptance, and had measured emittances within the range of 0.88-0.90. Through molten salt corrosion testing at 750degC it was found that SiC exhibits significantly lower mass change (-- 90 times lower) than Haynes 230 during 108 hours of salt exposure. The CTP TRIPLEX material performed significantly better than the SiC monolithic tube material in mechanical shock testing, breaking at an average height of 3 times that for the monolithic tubes. Through simulated rain thermal shock testing of CTP composite tubes at 800degC it was found that CTP's SiC composite tubes were able to survive thermal shock, while the SiC monolithic tubes did not. ACKNOWLEDGEMENTS * US Department of Energy Office of EERE for sponsorship of this project * Andrew Dawson of the DOE Office of EERE for Project Management, including the excellent technical insights that he provided throughout the project * Ken Armijo lead the Thermal Shock Testing activities * Cliff Ho and Julius Yellowhair led the Solar Spectrum Testing activities * Jeff Halfinger prepared the CTP specimens for each of the research tasks * Herb Feinroth provided guidance and input into the preparation for the test specimens and the associated research tasks * Alan Kruizenga collaborated with CTP to apply for and be awarded this project from DOE EERE. The scope for the project was developed by Alan together with CTP. * Rio Hatton and Jesus Ortega (student interns) helped with portions of the solar simulator testing, reflectance/emittance data collection, and image (including microscope) collection. * Kent Smith helped design and fabricate the high temperature molten salt corrosion setup * Jeff Chames and Javier Cebrian completed the microscopy for the molten salt corrosion test specimens * Amy Bohinsky (student intern) and Kevin Nelson helped complete the mechanical shock testing for the monolithic and composite tubes, including organizing the results for the final report. * Josh Christian and Daniel Ray helped with portions of the Thermal Shock Testing * Mark Stavig completed the polyethylene plug testing associated with the Thermal Shock Testing
The Sandia S-CO2 Recompression Closed Brayton Cycle (RCBC) utilizes a series of gas foil bearings in its turbine-alternator-compressors. At high shaft rotational speed these bearings allow the shaft to ride on a cushion of air. Conversely, during startup and shutdown, the shaft rides along the foil bearing surface. Low-friction coatings are used on bearing surfaces in order to facilitate rotation during these periods. An experimental program was initiated to elucidate the behavior of coated bearing foils in the harsh environments of this system. A test configuration was developed enabling long duration exposure tests, followed by a range of analyses relevant to their performance in a bearing. This report provides a detailed overview of this work. The results contained herein provide valuable information in selecting appropriate coatings for more advanced future bearing-rig tests at the newly established test facility in Sandia-NM.
The supercritical carbon dioxide (S-CO2) Brayton Cycle has gained significant attention in the last decade as an advanced power cycle capable of achieving high efficiency power conversion. Sandia National Laboratories, with support from the U.S. Department of Energy Office of Nuclear Energy (US DOE-NE), has been conducting research and development in order to deliver a technology that is ready for commercialization. Root cause analysis has been performed on the Recompression Loop at Sandia National Laboratories. It was found that particles throughout the loop are stainless steel, likely alloy 316 based upon the elemental composition. Deployment of a filter scheme is underway to both protect the turbomachinery and also for purposes of determining the specific cause for the particulate. Shake down tests of electric resistance (ER) as a potential in-situ monitoring scheme shows promise in high temperature systems. A modified instrument was purchased and held at 650°C for more than 1.5 months to date without issue. Quantitative measurements of this instrument will be benchmarked against witness samples in the future, but all qualitative trends to date are as to be expected. ER is a robust method for corrosion monitoring, but very slow at responding and can take several weeks under conditions to see obvious changes in behavior. Electrochemical noise was identified as an advanced technique that should be pursued for the ability to identify transients that would lead to poor material performance.
The supercritical carbon dioxide (S - CO2) Brayton Cycle has gained significant attention in the last decade as an advanced power cycle capab le of achieving high efficiency power conversion. Sandia National Laboratories, with support from the U.S. Department of Energy Office of Nuclear Energy (US DOE - NE), has been conducting research and development in order to deliver a technology that is rea dy for commercialization. There are a wide range of materials related challenges that must be overcome for the success of this technology. At Sandia, recent work has focused on the following main areas: (1) Investigating the potential for system cost re duction through the introduction of low cost alloys in low temperature loop sections, (2) Identifying material options for 10MW RCBC systems, (3) Understanding and resolving turbine degradation, (4) Identifying gas foil bearing behavior in CO 2 , and (5) Ide ntifying the influence of gas chemistry on alloy corrosion. Progress in each of these areas is provided in this report.