Particle Size Optimization of Thermochemical Salt Hydrates for High Energy Density Thermal Storage

Abstract

Thermal energy storage (TES) solutions offer opportunities to reduce energy consumption, greenhouse gas emissions, and cost. Specifically, they can help reduce the peak load and address the intermittency of renewable energy sources by time shifting the load, which are critical toward zero energy buildings. Thermochemical materials (TCMs) as a class of TES undergo a solid–gas reversible chemical reaction with water vapor to store and release energy with high storage capacities (600 kWh m−3) and negligible self-discharge that makes them uniquely suited as compact, stand-alone units for daily or seasonal storage. However, TCMs suffer from instabilities at the material (salt particles) and reactor level (packed beds of salt), resulting in poor multi-cycle efficiency and high-levelized cost of storage. In this study, a model is developed to predict the pulverization limit or Rcrit of various salt hydrates during thermal cycling. This is critical as it provides design rules to make mechanically stable TCM composites as well as enables the use of more energy-efficient manufacturing process (solid-state mixing) to make the composites. The model is experimentally validated on multiple TCM salt hydrates with different water content, and effect of Rcrit on hydration and dehydration kinetics is also investigated.