Sorption materials characterization and lab-scale reaction

The development of sorption for thermal energy storage (TES) can be an answer to reduce the CO2 emissions and resources depletion associated to the energy and building sectors. The main advantage of the sorption technology compared to other TES technologies is its high energy density. Nevertheless, long-term stability, corrosion, high cost, or the overall system efficiency are some factors that need to be addressed before launching it into the market. With the purpose of developing this technology, a physical characterization of the selected sorption material, its compatibility in terms of corrosion, and pilot tests were carried out. The selected sorption materials for this study are salt hydrates (MgSO4·7H2O and SrBr2·6H2O). Thus, the main reaction is the reversible process of the hydration and dehydration of the salt. The characterisation was done in terms of thermal conductivity; to this end a new methodology was developed using hot wire and a correlation was found between thermal conductivity and the studied parameters: compaction rate, material temperature, and thermal ageing of the material. Permeability tests on the sorption materials are also carried out to complement the conductivity results. Corrosion tests were done with an own developed method with the goal to study the adequacy of the sorption materials with stainless steel, copper, aluminium, and carbon steel as salt container materials. Copper turned out to be the worst choice when characterizing the SrBr2·6H2O, visual effects were also perceptible for carbon steel. On the other hand, MgSO4·7H2O is not so corrosive to the studied metals at a simple glance, further in depth analyses are still to be carried out. In parallel, a lab-scale prototype was designed and built in collaboration with CNR-ITAE, with the aim of actually studying experimentally the hydration and dehydration of the salts. The set-up consists on a reactor and condenser-evaporator pressurized vessels. The kinetics of the reaction as well as the experimental mass transfer of the sorption materials can be studied. The above mentioned experiments are a helpful contribution to determine the drawbacks and therefore addressing them as well as the correlation among physical properties and reaction conditions that can be favourable when upgrading sorption materials as a TES technology.