An Ultra-low-cost Thermal Energy Storage System using Reverse Osmosis Concentrate
Can RO concentrate salts be a suitable medium in Thermal Energy Storage cells to reduce the cost of TES and provide a beneficial reuse for RO concentrate thus reducing the cost of water Treatment?
Need and Benefit
As described by the National Academies Desalination document , S&T's Implementation plan, Regional S&T and AWT coordinators, various stakeholders in the regions and multitudes of other sources, concentrate management and proper disposal of it pose a significant barrier to wide spread adoption of inland desalination. The reject of the reverse osmosis water treatment process (aka brine, concentrate, ROC) is a mixture of salts that are dissolved in high salinity water. The ROC is classified as an industrial waste by the U.S. Environmental Protection Agency and can face regulatory limitations on disposal. The state-of-the-art of ROC disposal include deep-well injection, surface discharge to rivers, discharge to ocean, and evaporation ponds. All of the existing methods that are currently used in managing the ROC require releasing high concentrations of salt to the environment, leading to adverse effects. According to the National Academies and Reclamation, developing ROC disposal alternatives is one of the major priorities for water desalination research.
Many Reclamation regions would benefit from creating of new water supplies especially if costs are competitive to existing water sources. Use of desalination for inland application increases the availability of usable water by treating saline waters that are otherwise unusable and thus creating additional water supply for water short regions.
This study provides a novel solution to the concentrate issue and just as importantly provides energy storage for additional utilization when the energy is needed and not when the sun is shining. The thermal energy storage system made up of concentrate salts will capture the excess heat of solar panels during the day and will store that heat in concentrate salts and will then release that heat when the sun is not available. This solution will benefit both the water and renewable energy areas for Reclamation. Additional background information on Thermal Energy Storage (TES) is provided in the Other Comments Section.
The proposed solution converts ROC to a value proposition and creates a new market for ROC. The project aims to introduce a novel alternative for the ROC disposal by developing a technology that utilizes the ROC for storing thermal energy. TES systems are used to store thermal energy in the form of internal energy of a storage medium for future use. TES systems can be considered "Thermal Batteries" that store thermal energy instead of electricity. The most common application of TES systems are solar-thermal power plants and combined heat and power (CHP) systems. Molten salt mixtures (KNO3 and NaNO3) are mostly used as the storage medium in conventional TES systems due to their low vapor pressure, high specific heat, and chemical stability. The elevated demand for nitrate salts has led to higher storage fluid cost and increased cost of thermal energy storage.
According to DOE, revolutionary and evolutionary technologies are required to reduce the cost of TES below $15/kWht and to increase the TES temperature beyond 720 °C . The existing TES technologies are limited to 400 °C due to thermal degradation of the storage materials at higher temperatures. This proposal presents an innovative and ultra-low-cost approach to TES that contributes to meeting both DOE and BOR goals, i.e., reducing the cost of TES and introducing a novel application for management of ROC. The innovation of the proposed project is to demonstrate an ultra-low-cost, high-temperature, and brine-based TES system which meets the cost targets of DOE and is robust and scalable for different applications. This will provide relief for inland desalination by providing a beneficial use for ROC salts along with creating cheaper TES systems that can reduce the cost of energy simultaneously.
The adverse effects of releasing ROC to the environment is a well-known fact. 41% of desalination plants release the ROC to surface water, jeopardizing the loca
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