Analysis of regenerative thermal storage geometries for solar gas turbines

Abstract

Ceramic heat regenerators are suited to providing thermal storage for concentrating solar power stations based on a recuperated gas turbine cycle. Randomly packed beds of spheres and saddles; honeycombs and checker bricks were identified as potential regenerator inventory geometries. A parametric analysis of the heat transfer and pressure drop of each inventory type was conducted for two representative 6 hour storage systems. Due to the non isothermal nature of the sensible heat storage, the concept of a utilisation factor was introduced. This was used to determine the efficiency of each storage inventory for an allowable decrease in discharge temperature of 50 oC. The results demonstrate that with the correct choice of mass flux, all inventory types have a pressure drop below 1% of the compressor delivery pressure. The thermal modelling shows that checker bricks have the lowest utilisation factor and thus require a larger ceramic mass than the other inventories. Packed beds of saddles and honeycombs have the highest thermal performance but the lowest energy storage density. A packed bed of spheres is discussed as an effective inventory type that provides a good utilisation factor, acceptable pressure drop and a high energy storage density. Further investigation into the thermal-mechanical stresses in a packed bed is proposed for the development of this technology.