Liquid metals as efficient coolants for high-intensity point-focus receivers: implications to the design and performance of next generation CSP systems

Kurzfassung

To a large extent, the economic viability of CSP projects is influenced by the main parameters characterizing the receiver, such as concentration ratio, heat-flux-intensity and distribution, fluid outlet temperature and, naturally, the receiver efficiency. The design ranges for these parameters are in turn limited by the selection of the heat transfer fluid (HTF). In this work, two candidate liquid metals (LMs), namely sodium (Na) and lead-bismuth eutectic (LBE), are proposed as efficient HTFs that shall allow extending these design ranges beyond the current state-of-the-art, and thus contribution to the development of next-generation point-focus central receiver systems (CRSs). LMs offer two significant advantages compared to other HTFs used in CRSs. First, very high heat transfer coefficients can be achieved; roughly one order of magnitudes higher than with other liquids like molten nitrate salts, and many times the typical values of pressurized air; allowing to operate at higher heat flux intensities. Second, high fluid outlet temperatures can be achieved within stable liquids up to their boiling point (at 1 bar, Na: 883°C, LBE: 1533°C). Design considerations for implementing advanced concepts based on LM-cooling are analyzed in this work, evaluating their advantages and limitations. Previous experiences and theoretical evaluations indicate that a superior performance can be achieved with LMs, and the current state of technology reached a satisfactory maturity level for operating large-scale facilities.