Modeling of powder bed dynamics in thermochemical heat storage

Abstract

Thermochemical energy storage in the CaOCa(OH)2 system offers high energy capacity and near perfect reversibility and is one of the most promising technologies for thermal energy storage. In particular, fixed bed reactors are being investigated for their low cost and simplicity. However, upscaling of these reactors is hindered by changes in heat and mass transfer through the powder bed due to compaction and agglomeration of the powder bed during repeated cycling. Therefore, we develop a model for the dynamics of powder beds in thermochemical reactors in response to gas flow and expansion and contraction during repeated cycling. The model couples a model for the reactive transport in the powder bed to a large strain elastoplastic model for its deformation and compaction. The constitutive relations for the powder bed are based on modified DruckerPragerCap plasticity, including a hardening mechanism. For comparison with experiment, a parametrization of the model using only flow tester data is presented. The capabilities of the new model are demonstrated by simulating multiple charge-discharge cycles, where the numerical results show irreversible effects that cannot be simulated with static models, such as successive powder compaction during cycling. The numerical results are compared with experimental data where qualitative agreement is found. Furthermore, the new model is compared with existing static models and the differences between the models are discussed. Finally, we give an outlook on how the prediction of powder compaction can lead to the design of optimized reactor geometries and cycling protocols.