Thermal Performances of a High Temperature Air Solar Absorber Based on Compact Heat Exchange Technology

In the framework of the French PEGASE project (Production of Electricity by GAs turbine and Solar Energy), CNRS/PROMES laboratory is developing a 4 MWth pressurized air solar receiver with a surface absorber based on a compact heat exchanger technology. The first step of this development consists in designing and testing a pilot scale (1/10 scale, e.g., 360 kWth) solar receiver based on a metallic surface absorber. This paper briefly presents the hydraulic and thermal performances of the innovative pressurized air solar absorber developed in a previous work. The goal is to be capable of preheating pressurized air from 350 °C at the inlet to 750 °C at the outlet, with a maximum pressure drop of 300 mbar. The receiver is a cavity of square aperture 120 cm × 120 cm and 1 m deepness with an average concentration in the aperture of more than 300. The square shaped aperture is chosen due to the small scale of the receiver; indeed, the performances are not enhanced that much with a round aperture, while the manufacturability is much more complicated. However in the perspective of PEGASE, a round aperture is likely to be used. The back of the cavity is covered by modules arranged in two series making the modular and multistage absorber. The thermal performances of one module are considered to simulate the thermal exchange within the receiver and to estimate the energy efficiency of this receiver. The results of the simulation show that the basic design yields an air outlet temperature of 739 °C under design operation conditions (1000 W/m² solar irradiation, 0.8 kg/s air flow rate). Using the cavity walls as air preheating elements allows increasing the air outlet temperature above 750 °C as well as the energy efficiency up to 81% but at the cost of a critical absorber wall temperature. However, this wall temperature can be controlled by applying an aiming point strategy with the heliostat field.