Session: 06-03: Concentrated Solar Power II -- Power Block and Components

Paper Number: 130951

130951 - Helium Gas Brayton Cycle and Rankine Cycle Combined System With PCM Thermal Storage for Efficient CSP System 

Abstract: 

It is desirable for concentrating solar power system to have greater thermal efficiency. This makes it reasonable to run thermal power systems at high temperatures with Brayton gas cycle and in combination with Rankine cycle, which uses the energy from the exhaust of the gas turbine with water or organic liquid as the working fluid.  Recently, with the development of heliostat concentration technology and its capability of efficient and high concentration ratio solar collection throughout the day, it becomes possible to have a solar receiver being able to get temperatures of 1000-1050 °C and the heat transfer fluid can reach a temperature at a level of 950 ^oC for thermal storage to provide heat via heat exchange for power generation at night. With such a high temperature heat supply, Brayton gas cycle and Rankin cycle combined power generation system becomes realistic. Using helium gas as the heat transfer fluid to bring the heat from solar receiver to power cycle system and to thermal energy storage system is believed to be a very good option, as helium is an inert gas with no corrosion to metals and has relatively high thermal conductivity. Importantly, helium gas also has been well recognized and used for high temperature nuclear power system Brayton cycles.  In order to extend the nightly power system operation from sunset to sunrise, thermal storage needs to provide heat for 16 hours. Therefore, high temperature phase change material (PCM) should be considered to take the benefit of high heat of fusion for thermal storage, and thus a large quantity of heat can be stored in a compact volume for power generation.  Among the high temperature PCM materials, sodium chloride (NaCl) is selected for use in this study, which has a melting point of 801 ^oC and heat of fusion of 520kJ/kg that is more than 1/5 of the latent heat of water vaporization. Extra sensible energy can also be stored in the liquid NaCl after it is melted, since the boiling point of NaCl is as high as 1465 ^oC. The low price and the large quantity of availability of NaCl is very attractive for low-cost thermal storage application. It is well known that anhydrous NaCl salts under anaerobic environment has sufficiently low corrosion to high temperature alloys. Thermodynamic analysis to the combined power system by Brayton helium gas cycle and Rankine steam cycle has been conducted for the objective of obtaining the highest overall energy conversion efficiency. Operation in daytime (8 hours) with high temperature helium gas directly from the solar receiver and the operation in the night (16 hours) with the helium gas temperature dominated by the stored thermal energy are simulated and optimized.

Presenting Author: Sheng Li University of Arizona

Presenting Author Biography: Sheng Li is currently a Ph.D. candidate in the Department of Aerospace and Mechanical Engineering at the University of Arizona. He has a bachelor degree in thermal science and energy engineering.

Authors:

Sheng Li University of Arizona
Ahmed Gamil University of Arizona
Peiwen Li University of Arizona