Session: 06-01: Thermal Energy Storage

Paper Number: 130926

130926 - Design & Experimental Investigations of an Internally Insulated Tank for the Ternary Chloride Molten Salt at 720℃ for Gen 3 Csp 

Abstract: 

In 2021, the National Renewable Energy Laboratory (NREL) published results for a pilot project for a high-temperature concentrating solar power (CSP) system using molten ternary chloride salt for energy storage, aiming to enhance the efficiency and sustainability over the traditional storage methods [https://doi.org/10.2172/1807668]. The project, named “Gen3 Liquid Pathway”, did not advance to the construction phase, mainly due to the significant risks linked with the handling and storing of molten salt in the molten salt tank, which is crucial for the CSP system’s operation. Following this, the U.S. Department of Energy supported NREL in developing and testing a small molten salt storage tank (approx. 1.5-m diameter) to evaluate whether it could safely store the proposed molten ternary chloride salt (MgCl₂+KCl+NaCl). This tank contains an internal refractory lining featuring a layer of graphite foil to provide a barrier against the liquid salt. This graphite lining was a critical enhancement to the design, aimed at safeguarding the underlying insulation layers from being wetted by the salt. This paper includes the design and experimental performance evaluation of the graphite liner used in the storage tank. The design of the graphite layer involves using thin sheets of commercial graphite foil adhered with graphite adhesive. This layer is positioned between a protective refractory brick on the salt-facing "hot face" and an underlying insulating firebrick. This design, without the inclusion of graphite, was developed and documented in the referenced report for a MW-scale tank. Alterations in the current project are inclusion of the graphite layer and the reduction of the hot face brick thickness from 9 inches (22.8 cm) to 4.5 inches (11.4 cm). The hotface modification was made to decrease the tank shell diameter and is not expected to significantly affect the liner's insulating properties, which is considered sufficient for the tank’s modest size and the short duration of the test. A bench-scale test involved a 100-hour run under nitrogen at 600℃ to confirm liquid-tight stability of the graphite foil. For the ~200-kg salt tank test, the procedure involves gradually increasing the salt temperature to a maximum of 720℃ and maintaining it for a minimum of 30 days. Data on time, temperatures, and heat flux are collected during this period to evaluate the insulation's effectiveness. After the 30-day test period, the storage tank is emptied, and the liner is inspected for any signs of salt penetration and damage.

Presenting Author: Prashant Saini National Renewable Energy Laboratory (NREL)

Presenting Author Biography: Hi, I am Prashant. I worked as a researcher at NREL. I completed my Ph.D. in Mechanical Engineering with a specialization in Thermal and Fluid Engineering. I worked on solar energy harvesting and its utilization in different industrial applications. I have around 8 years of experience in solar thermal systems. My specialty areas include ray tracing methods, CSPs, thermal energy storage, heat exchangers, nanoparticles, metal foams, turbulators, fluid flow analysis, and heat transfer mechanisms.

Authors:

Prashant Saini National Renewable Energy Laboratory (NREL)
Nikolas Conmy NREL
Youyang Zhao NREL
Jonathan Martin NREL
Christa Schreiber NREL
Judy Netter NREL
Craig Turchi NREL