Simulation of an ROC-Based Thermal Energy Storage System in Charge and Discharge Cycles

In this paper, Computational Fluid Dynamics (CFD) is employed to investigate the heat transfer characteristics of Reverse Osmosis Concentrate (ROC) as an alternative, low-cost thermal energy storage medium. Thermal energy storage is a critical component for increasing efficiency and dispatchability of solar thermal and combined heat and power plants. The byproduct of water desalination, ROC, is classified as an industrial waste by the U.S. Environmental Protection Agency as it has negative effects on vegetation and sea-life. Currently, ROC disposal includes deep-well injection, surface discharge to rivers, discharge to the ocean, and evaporation ponds. The composition and thermal properties of ROC salt vary depending on the original source of feedwater. Transient models are utilized to understand the heat transfer between the heat transfer fluid and storage fluid (i.e., ROC) over time. This simulation also provides valuable information in determining the optimal operating conditions of the thermal energy storage system. This information will be used in conjunction with a cost analysis, focused on the transportation, processing and containment cost of the energy storage, that aims to determine the economic feasibility of ROC technology in large scale, commercial applications.