Thermal performance evaluation of lining materials used in thermal energy storage for a falling particle receiver based CSP system

In this study, experiments were conducted on a cylindrical-shaped Thermal Energy Storage (TES) system for a novel Concentrating Solar Power (CSP) falling particle receiver system. The TES is to be used for storing heated solid particles. The main objective of the study was to evaluate the thermal performance of some candidate materials of construction for the walls of TES Hot-bin. In particular, emphasis was on the calculation of the rate of heat loss over a prescribed period of time, since this parameter was critical to the overall performance of a high-temperature solar energy plant. The construction materials were selected in order to have low thermal conductivity and the ability to withstand cyclic high temperatures without failure. An experiment was continuously run in which the temperature was maintained at about 300 °C, 500 °C, and 700 °C respectively, allowing steady state conditions to be achieved for sustained period of time. To simulate the presence of a high-temperature storage material, a heater inserted in the centerline of the interior of the Hot-bin, and the thermocouples were installed to measure the temperatures at various locations throughout the composite wall. Results show that the thermal conductivity of insulating firebrick remains low (approximately 0.22 W/m·K) at an average layer temperature as high as 640 °C, but it was evident that the addition of mortar had an impact on its effective thermal conductivity. Results also show that the thermal conductivity of perlite concrete is very low, approximately (0.15 W/m·K) at an average layer temperature of 360 °C. This is evident by the large temperature drop that occurs across the perlite concrete layer. Due to the large daily ambient temperature swing, a measurement of the thermal conductivity of reinforced concrete was estimated by applying a 3D model of the reinforced concrete layer. Thermal conductivity of the reinforced concrete layer is about 1.936 W/m·K at an average temperature 52.5 °C. Based on the estimated thermal conductivity values of layers, heat loss was found to be 1.39%, 2.58% and 4.59% at 300 °C, 500 °C and 700 °C respectively. Furthermore, inspection of the materials used to construct the TES system showed that they remained intact and did not show signs of cracking or wearing. These results showed that the high-temperature TES systems can be constructed of readily available materials and yet meet the heat loss requirements for a falling particle receiver system, thereby contributing to reducing the overall cost of concentrating solar power systems. An important secondary outcome of this study is building a database for the thermal conductivity of some masonry materials at high temperatures. These results should be useful for future studies, especially those that focus on numerical modelling of TES bins.