Session: 03-01 Low Temperature Thermal Storage

Paper Number: 142380

142380 - Kinetic Behavior of Hydration of Thermochemical Salts for Thermal Energy Storage 

Abstract: 

Thermochemical Energy Storage (TCES) is one of the technologies which can be used for thermal energy storage, where the thermal energy is stored in chemical bonds. One reaction of interest for providing thermal energy to buildings is the reversible hydration-dehydration reaction of salt hydrates. Salt hydrates are hygroscopic material, which when introduced to water vapor, undergo a reversible adsorption reaction whereby thermal energy is released. Conversely, when thermal energy is provided to salt hydrate, it undergoes endothermic dehydration reaction. Several salt hydrates have been identified as a potential candidate for TCES, e.g., MgSO₄, SrCl₂, CaCl₂, K₂CO₃, and SrBr₂. Furthermore, blends of various salts have also been proposed. The hydration kinetics is one of the important criteria for evaluating salts for TCES because it is linked to the potential power output and temperature lift in a reactor. In general, salt hydrates with faster reaction kinetics are advantageous. However, prior research on the reaction kinetics of salt hydration is limited compared to other parameters such as energy density. The objective of this study is to broaden the understanding of hydration reaction rates of different hygroscopic salts by investigating samples at the same environmental conditions and with the same methodology to aid in comparison between salts. In this study, samples of pure salts - MgSO₄, SrCl₂, CaCl₂ and blend of these pure salts are studied. A series of hydration experiments are conducted. In each experiment, the salt samples were first dried in a flow of dry nitrogen at 110 °C. Then a small amount of the salt sample was distributed in thin layer and placed in the hydration chamber. This thin layer helped to reduce reaction rate limitations due to diffusion of water vapor through the sample. Hydration temperatures from 15°C to 45°C and relative humidity (RH) values from 40% to 65% were selected for the study. These conditions were selected because they represent the temperature and relative humidity at which the salt may be hydrated in a thermochemical reactor. The reaction rates were measured by weighing the samples at regular intervals. The experiments revealed that hydration reaction rate and equilibrium water uptake are dependent on water vapor pressure value. Out of all the samples, CaCl₂ tends to achieve a given water uptake amount faster than other salts. The addition of CaCl₂ to the other salts also tends to increase the rate of water uptake of the blend relative to the reaction rate of the non-CaCl₂ pure salt. However, the blend with higher weight percent of CaCl₂ tend to readily deliquesce, which is undesirable.

Presenting Author: Shishir Kumar Das North Dakota State University

Presenting Author Biography: Shishir is a graduate research assistant at North Dakota State University. He is working in thermochemical energy storage under the guidance of Dr. Adam C. Gladen.

Authors:

Shishir Kumar Das North Dakota State University
Adam C. Gladen North Dakota State University