Design and Preliminary Evaluation of a Supercritical Carbon Dioxide Brayton Cycle for Solar Dish Concentrator Clean Energy Production
As we move toward energy independence and more ambitious clean energy goals, solar energy research must push the efficiency limits of traditional energy generation systems. Increases in efficiency can be achieved by increasing the hot temperature of the power cycle. Recent research demonstrates the potential for increased efficiency and a vastly smaller component size when supercritical carbon dioxide Brayton power cycles are used. Concentrated solar and nuclear heat sources are capable of achieving the high working fluid temperatures needed for significant efficiency gains. This NSF EPSCoR funded, experimental research system is designed to exploit the uniquely immense solar irradiance of the Mojave Desert, coupling a solar dish concentrator with the UNLV supercritical carbon dioxide (SCO2) Brayton cycle, fabricated on campus at the UNLV Center for Energy Research and the UNLV Machine Shop. This, in conjunction with dry cooling, compounds the capacity for increased efficiency with trivial water consumption and decreased environmental and geographical footprints.
Photographic flux mapping was used to provide solar flux information leading to the custom design and on-site fabrication of the solar receiver. A custom air-cooled heat exchanger with expansion capabilities was designed and fabricated for heat rejection. To further increase efficiency, internationally collaborative custom minichannel heat exchangers from the research team at Xi’an Jiaotong University, P.R. China, were added in both zigzag and straight channel geometries; these heat exhangers are installed in parallel, with isolation valves, for experimental comparison and singular recuperation in the system. The turbine and compressor housing exhibits a modular design to allow ease of desired experimental modifications. All components are mounted on an SAIC dish concentrator solar tracking system for on-sun experimental testing. A computational model of the solar receiver and heat rejection system, as well as the entire power cycle, has been created in Engineering Equation Solver (EES).
On-sun experimental tests of the solar receiver and heat rejection systems have indicated system capability to both reach high temperatures and reject the heat required to achieve accelerated efficiencies. Once high efficiency temperature ranges are achieved, efficient turbomachinery is required for high efficiency operational success. Fabrication issues and resolutions surrounding the machining of small turbomachinery in this high temperature environment are described as a part of this research. Of particular consequence are issues surrounding the design and fabrication of the turbo-compressor shaft to housing interface. Bearing issues prove to be the core limitation preceding successful operational performance of the turbo-compressor unit. Decisions leading to the successful resolution to this issue are also described.
This concentrated solar research system is a demonstration of the innovative component and system design needed to reach the next level in clean solar energy using trivial water consumption. The experimental and computational components support previous theories for the role of concentrated solar in clean power generation systems with increased efficiencies. This experimental system provides proof of concept for supercritical carbon dioxide Brayton cycles with solar concentrator technology, contributes to the advancement of SCO2 Brayton cycle component fabrication processes, and displays the capacity of UNLV to move this SCO2 turbo-compressor unit toward commercialization.