Simulation of a zeolite thermochemical heat storage reactor: Impact assessment of isotherm model selection

Abstract

Efficient modeling of thermochemical heat storage reactors is required to predict their performance in various operating conditions and optimize their design. Such modeling necessitates an accurate description of the properties of storage materials, which is still challenging to this day. This paper specifically investigates the influence of the choice of the sorption isotherm model. To this aim, the Langmuir, Dubinin-Astakhov (DA) and modified Brunauer-Emmet-Teller (BET) isotherm models are studied. The 1D model of an open fixed bed reactor based on the hydration and dehydration of zeolite 13X is presented. The model couples heat and mass transfer and uses the linear driving force approximation. Experimental investigations are also performed to characterize the sorption equilibrium of the material, its adsorption kinetics at the reactor scale and the resulting heat storage performance. The model is validated simultaneously on the basis of mass and of heat transfer measurements (i.e., breakthrough and temperature curves).The BET isotherm is shown to be the most relevant for the description of water adsorption on zeolite 13X because it considers multilayer adsorption. It fits the experimental isotherm best. At the reactor scale, the modified BET model also provides the best results, closely followed by the DA model. Still, for consistent predictions, the characterization of the chosen sorbent (i.e., the experimental data used to correlate the isotherm model or the heat of sorption) is of utmost importance and the initial water loading must be adequately specified.