(506d) Dynamic Simulation and Optimization of an Adsorption Heat Storage

The energy transition requires the extensive use of renewable energies, including those from intermittent sources such as solar and wind energies. For heat consumption in buildings and in industrial processes, solar thermal heat represents a good alternative to fossil fuels. However, the production and consumption of heat are variable and asynchronous. A thermal storage is therefore required to satisfy the heat demand. Adsorption heat storage is a promising technology since it presents a high energy density ensuring its compacity. Moreover, the heat is stored as a chemical potential, resulting in negligible heat losses. In an adsorption storage connected to a solar thermal system, the solar excess heat is used to desorb the molecules (endothermic regeneration of the adsorbent) and the exothermic adsorption is performed when heat needs to be recovered. Currently, adsorption heat storage is not competitive against sensible or latent heat storage due to the high cost of material. Nonetheless, the choice of adsorbent/adsorbate couple, the design of the adsorption column as well as the operating parameters impact the energy density of the storage (Lefebvre and Tezel, 2017). Thus, optimizing the design and operation of the adsorption heat storage could help improve its economic viability.

This study aims at modeling and optimizing an adsorption heat storage to show its ability to satisfy the heat demand of a building with renewable heat. For integration in a building, an open loop system with water chosen as the adsorbate ensures a simpler structure. The adsorbent chosen is a zeolite 13X. The design of the system is retrieved from an experimental pilot in (Tatsidjodoung et al., 2016).

The model used was built on a previous detailed model developed by (Ferreira et al., 2021), and validated with the experimental data from (Tatsidjodoung et al., 2016). The model is based on mass balances on the fluid components, air and water, and on energy balances on the fluid and the porous media. A Linear Driving Force (LDF) model (Glueckauf, E., 1955) is used to represent the adsorption process, including the different mass transfer resistances: external, macroporous and microporous. The equilibrium model chosen is the Aranovich–Donohue model as formulated by (Ahn. H., 2019). The differential-algebraic system of equations is solved with ode15s in MATLAB. Some simplifying assumptions have been implemented to obtain a simple model suitable for optimization: constant thermophysical properties (except for the fluid density), negligible axial dispersion and fluid and solid at the same temperature. Moreover, the spatial discretization scheme has been improved and finite volumes are considered to ensure mass conservation.

The results of the dynamic simulation of an adsorption phase show the impact of the operating parameters on the energy released. The duration of the phase, the temperature lift obtained, and the overall quantity of energy recovered depend on the inlet fluid temperature, humidity, and velocity, as well as the size of the storage. It seems that a dynamic optimization could help to choose the best operating parameters to satisfy a dynamic heat demand at the lowest cost. In future work, the size of the storage tank as well as the operating parameters will be optimized in some case studies for the adsorption phase. The integration of the adsorption heat storage into a solar thermal house heating system will then be implemented and the overall system optimized.

References

Ahn, H., 2019, Equilibrium theory analysis of thermal regeneration of a humid adsorption column: Selection of optimal hot purge gas temperature, Chem. Eng. Res. Des., 151, 91–99.

Ferreira, S., Sochard, S., Serra, S., Marias, F., Reneaume, J.-M., 2021, Modelling of an Adsorption Heat Storage System and Study of Operating and Design Conditions, Processes, 9, 1885.

Glueckauf, E., 1955, Theory of chromatography. Part 10—Formulæ for diffusion into spheres and their application to chromatography. Trans. Faraday Soc., 51, 1540–1551

Lefebvre, D., Tezel, F. H., 2017, A review of energy storage technologies with a focus on adsorption thermal energy storage processes for heating applications, Renewable and Sustainable Energy Reviews, 67, 116-125

Tatsidjodoung, P., Le Pierrès, N., Heintz, J., Lagre, D., Luo, L., Durier, F., 2016, Experimental and numerical investigations of a zeolite 13X/water reactor for solar heat storage in buildings, Energy Convers. Manag, 108, 488–500.