Liquid Metal as a Heat Transport Fluid for Thermal Solar Power Applications

Abstract

In order to increase the thermal efficiency and produce process heat for hydrogen production, the operating temperature of the heat transfer fluid in thermal solar plants needs to increase. In addition reaching 900°C would also increase the heat storage density and the efficiency of the thermodynamic cycle by using a combined cycle for electricity production. The benefits of hydrogen (e.g., for fuel cells) and a more efficient thermodynamic cycle would allow a plant to have a higher energy output per square acre of land use, thereby increasing its economic competiveness.Today, solar thermal plants do not operate at these high temperatures due to the fact that conventional heat transport fluids begin to disintegrate around 600°C [1,2]. For non-solar applications, low melting-temperature metals, such as wood's metal and lead- bismuth eutectic alloy, have been examined as heat-transport media, because of the large temperature ranges over which they remain liquid. Lead-bismuth eutectic alloy (LBE; 45% Pb, 55% Bi) melts at 125°C and does not boil until 1670°C, making it an ideal heat-transfer medium for application in thermal solar power [3]. The main obstacle to using LBE is finding structural materials that can withstand the harsh corrosion environments at high temperatures. In this work the key issues of materials exposed to liquid metal are described while initial data on carious steels tested in liquid metal are provided. While corrosion is a significant issue in this environment, mechanical failure of steels in liquid metal are discussed as well.