Flow and heat transfer in fluidized bed tubular solar receivers ; Écoulement et transfert de chaleur dans les récepteurs solaires tubulaires à lits fluidisés

To produce electricity from solar energy with a concentrated solar power plant, the use of particles as both heat transfer fluid in the solar receiver and storage medium appears to be very attractive to increase the global plant cost and efficiency. In this context, PROMES Laboratory (France) develops since the 2010s a concept of solar receiver using a dense suspension of fluidized particles as heat transfer fluid. The particles circulate upward in metallic tubes of high aspect ratio (height over diameter), exposed to the concentrated solar flux, thanks to both an overpressure in the vessel fluidized bed and a secondary air injection at the bottom of the tubes. Several numerical and experimental studies at low scales demonstrated the interest of such solar receiver concept by reaching particle temperature at the outlet of the receiver higher than 700 °C. These high temperatures are higher than the limits imposed by the heat transfer fluid commonly used in industrial solar towers. It enables the use of highly efficient thermodynamic cycles at the outlet of the receiver. However, it results in strong thermal losses that decreases the overall plant efficiency.In order to decrease these losses and to increase the receiver efficiency, a simplified thermal model of a solar receiver at industrial scale has been developed. A cavity is integrated around the solar absorber, constituted of hundreds of tubes, and the influence of the cavity geometry on the receiver thermal performances has been studied. It comes that the aperture area of the cavity and its distance with the receiver strongly modify the thermal losses of the system. With a receiver power of 50 MWth, a thermal efficiency of 85 % is then obtained for a cavity aperture of 25 m², proving the interest of the latter to reach similar efficiencies than the receivers using molten salts. One of the main drawbacks of this technology of solar receiver using fluidized particles is the apparition of several fluidization regimes in the receiver tubes depending on the ...