(44b) Particle-sCO2 Primary Heat Exchanger Technology for Moving Particle Thermal Energy Storage Systems in High Temperature sCO2 Based CSP Plants

Renewable energy systems tend to be intermittent with high capital costs and low thermal-to-electric conversion efficiency. In order minimise costs, they would need to operate near full capacity, which is one reason for their limited integration in the electric grid mix. The penetration of renewable energy generators on the electric grid is significantly improved by integrating long duration energy storage systems necessary to match production with demand. Various energy storage technologies are being considered and developed. These include thermal systems using sensible storage materials (molten salt, solids and water) and phase change materials (organic, inorganic, liquid air energy storage); mechanical storage systems (compressed air energy storage, pumped energy storage, gravity and flywheels); electrochemical storage or batteries (Li-ion, Flow, Lead Acid) and chemical energy storage (hydrogen, ammonia, methanol).

In this paper, we discuss a heat exchanger technology that allows integrating solid particle based thermal storage systems with an advanced concentrated solar energy systems. Concentrating solar power (CSP) with thermal energy storage has the potential to provide dispatchable renewable energy with increased capacity factor. CSPs have evolved from oil based trough systems (~400⁰C) or molten salt-based (~565⁰C) Steam Rankin cycles to systems targeting higher than 700⁰C turbine inlet temperature by coupling with a high-efficiency supercritical carbon dioxide (sCO₂) power cycles.

Solid carbo, ceramic, or sand particles suitable for high operating temperatures have the advantage of being low cost and abundant heat storing medium with superior thermal properties including high solar absorbance. These small particles, sensible thermal energy storage media, can work with various receiver configurations and help meet low levelized cost of electricity and cost of energy storage. However, there is a need to have a reliable and low cost, high effectiveness heat exchanger between the thermal storage media (particle) and working fluid (sCO2). One technology that is being developed and tested for the particle-to-sCO₂ primary heat exchanger (PHE) is diffusion bonded plate sub-assemblies stacked with gaps (enclosed with side bars) creating a moving particle bed. The bonded sub-assemblies use plates with chemically etched fluid flow channel network suitabile for high temperature and pressure sCO2 fluid and popularly used in sCO2 power cycles as recuperators and coolers. The narrow slots between the bonded sub-assemblies provide compact moving particle bed with higher heat transfer contact.

In comparison with the conventional alternatives that uses tubular fluidized bed designs, moving particle monolithic plate designs result in higher overall heat transfer coefficient with added advantage of being easier for system integration and packaging due to their compactness. Demonstration scale test results and future solid side heat transfer enhancement technologies will also be presented in this paper.