Thermochemical storage systems (TCM) constitute a promising alternative for the exploitation of solar energy, allowing the decoupling of energy availability (summer) from its demand in the context of domestic heating (winter). During the winter season, peaks in heat demand constitute a significant disturbance for the electricity system, especially when a large part of the heat demand will be satisfied by electrically powered systems such as heat pumps. Seasonal thermal storage would allow for their more effective management, bringing benefits in terms of optimization of the generation park, reduction of fossil fuels and fewer critical issues in the electricity grid.

However, TCM-based seasonal energy storage requires the management of high volumes of materials, even in domestic applications; a solution to this problem is that offered by separate reactor technology, based on the physical separation of the reaction vessel from the long-term storage tanks.

This plant setup, an alternative to fixed bed reactors, would make it possible to 1) reduce investment costs, 2) make seasonal storage more compact and 3) bring greater flexibility and scalability to the system. On the other hand, a system for handling the pellets of material used for storage is required, which can be a critical aspect during the operation of the plant.

In this context, a thermochemical storage material handling system capable of operating in fully automatic mode was designed and installed in the RSE laboratory facility. The objective is to demonstrate its effectiveness through batch movement tests, alternated with reactive phases of heat accumulation and release. To evaluate the energy performance of the system and the material, an experimental campaign was carried out using Zeolite 13X in vapor capture/heat release tests in different operating conditions; after each adsorption or regeneration test, the handling procedure for the replacement of material was carried out.

While the material showed good performance in the vapor absorption/heat release phases, on the other hand the zeolites showed a tendency to shatter and pulverize following several handling cycles, leading to plant problems due to sedimentation and cementification of powdered sorbent.

To further analyze the reactor operation during the tests, mathematical modeling was carried out; the resulting model is based on 1-D numerical definition of the energy and material balances for each elementary volume in which the reactor and sorbent pellets are discretized. The model considers the heat capacity of the reactor metal walls and the heat losses to the environment through the insulation. In addition, the model has been integrated with a graphical user interface (GUI) from which simulations can be started and monitored.

Lastly, the validation of the model was performed by comparing the numerical output with the experimental results; the reported percentage mean square error has shown to be lower than 10% for all analyzed cases.

The Report is available on the Italian site