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Article

Thermochemical Heat Storage in a Lab-Scale Indirectly Operated CaO/Ca(OH)2 Reactor—Numerical Modeling and Model Validation through Inverse Parameter Estimation

Department of Hydromechanics and Modelling of Hydrosystems, University of Stuttgart, 70569 Stuttgart, Germany
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Appl. Sci. 2021, 11(2), 682; https://doi.org/10.3390/app11020682
Received: 17 December 2020 / Revised: 30 December 2020 / Accepted: 8 January 2021 / Published: 12 January 2021
(This article belongs to the Special Issue Advances in Porous Materials for Energy Storage)
Calcium oxide/Calcium hydroxide can be utilized as a reaction system for thermochemical heat storage. It features a high storage capacity, is cheap, and does not involve major environmental concerns. Operationally, different fixed-bed reactor concepts can be distinguished; direct reactor are characterized by gas flow through the reactive bulk material, while in indirect reactors, the heat-carrying gas flow is separated from the bulk material. This study puts a focus on the indirectly operated fixed-bed reactor setup. The fluxes of the reaction fluid and the heat-carrying flow are decoupled in order to overcome limitations due to heat conduction in the reactive bulk material. The fixed bed represents a porous medium where Darcy-type flow conditions can be assumed. Here, a numerical model for such a reactor concept is presented, which has been implemented in the software DuMux. An attempt to calibrate and validate it with experimental results from the literature is discussed in detail. This allows for the identification of a deficient insulation of the experimental setup. Accordingly, heat-loss mechanisms are included in the model. However, it can be shown that heat losses alone are not sufficient to explain the experimental results. It is evident that another effect plays a role here. Using Bayesian inference, this effect is identified as the reaction rate decreasing with progressing conversion of reactive material. The calibrated model reveals that more heat is lost over the reactor surface than transported in the heat transfer channel, which causes a considerable speed-up of the discharge reaction. An observed deceleration of the reaction rate at progressed conversion is attributed to the presence of agglomerates of the bulk material in the fixed bed. This retardation is represented phenomenologically by mofifying the reaction kinetics. After the calibration, the model is validated with a second set of experimental results. To speed up the calculations for the calibration, the numerical model is replaced by a surrogate model based on Polynomial Chaos Expansion and Principal Component Analysis. View Full-Text
Keywords: thermochemical heat storage; DuMux; bayesian inference; agglomeration of the reactive bulk thermochemical heat storage; DuMux; bayesian inference; agglomeration of the reactive bulk
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MDPI and ACS Style

Seitz, G.; Mohammadi, F.; Class, H. Thermochemical Heat Storage in a Lab-Scale Indirectly Operated CaO/Ca(OH)2 Reactor—Numerical Modeling and Model Validation through Inverse Parameter Estimation. Appl. Sci. 2021, 11, 682. https://doi.org/10.3390/app11020682

AMA Style

Seitz G, Mohammadi F, Class H. Thermochemical Heat Storage in a Lab-Scale Indirectly Operated CaO/Ca(OH)2 Reactor—Numerical Modeling and Model Validation through Inverse Parameter Estimation. Applied Sciences. 2021; 11(2):682. https://doi.org/10.3390/app11020682

Chicago/Turabian Style

Seitz, Gabriele; Mohammadi, Farid; Class, Holger. 2021. "Thermochemical Heat Storage in a Lab-Scale Indirectly Operated CaO/Ca(OH)2 Reactor—Numerical Modeling and Model Validation through Inverse Parameter Estimation" Appl. Sci. 11, no. 2: 682. https://doi.org/10.3390/app11020682

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