Salt Hydrates for Thermochemical Storage of Solar Energy: Modeling the Case Study of Calcium Oxalate Monohydrate Dehydration/Rehydration under Suspension Reactor Conditions

Abstract

A way to overcome issues related to the exploitation of solar energy is to refer to concentrated solar power technology coupled with systems for thermochemical energy storage (TCES) as a means to store solar energy for theoretically unlimited periods and distances at ambient temperature and with a high energy storage density. As potential candidate materials for TCES, salt hydrates are of particular interest. In this work, we focus our attention on the behavior of the coupled calcium oxalate monohydrate/anhydrous (COM/COA), a case study deserving investigation in the literature. To put the basis for large-scale application, a suspension stirred reactor has been conceptualized here with the idea of performing the process in a suspension medium. This work illustrates and discusses a modeling activity where heat balances for COM dehydration (heat charging stage)/COA rehydration (heat discharging stage), transport phenomena, and kinetics for COM dehydration are scrutinized with the corresponding evaluation of the characteristic time scales. The following aspects were critically analyzed: profiles for mass flow rates of service oil vs time for heating and reaction phases during dehydration, effects of water/COA and COA/oil feed ratios on the final temperature reached during COA rehydration, time–temperature, and time–water mole profiles inside a spherical COM particle upon dehydration, along with the results for stored/released energy (upon charging/discharging stages), characteristic times for heat transfer, mass transfer, water vapor bubble rising, and kinetics referred to the dehydration stage. Finally, the likeliness of controlling mechanisms as a function of particle and water vapor bubble size during COM dehydration has been discussed with the aid of a synoptical graph.

Characterization of Ca-Dicarboxylate Salt Hydrates as Thermochemical Energy Storage Materials

“…A systematic search algorithm screening for chemical reactions suitable to become part of a thermal energy storage system proposed the calcium oxalate monohydrate/calcium oxalate (CaC 2 O 4 •H 2 O/CaC 2 O 4 ) system as such a potential reaction [20]. The material was analyzed and subsequently characterized, confirming the theoretically promising data by showing excellent cycle stability, full reversibility of reaction, and tuneability of the storage temperature via varying the water vapor concentration [21,22]. Based on the data for the CaC 2 O 4 •H 2 O/CaC 2 O 4 system, a small library of calcium dicarboxylate salt hydrates (1-5f) was chosen to conduct the study of these calcium salt hydrates to investigate whether some of the candidates share the strengths of the oxalate or can even outperform it.…”

A Review on Solar Drying Devices: Heat Transfer, Air Movement and Type of Chambers

“…This process stores energy by using high-energy chemical processes. In this case, the heat stored depends on the amount of storage material, the endothermic heat of the reaction and the extent of conversion [136][137][138].…”