The influence of gas–solid reaction kinetics in models of thermochemical heat storage under monotonic and cyclic loading

Power generation based on the Ca(OH)2/ CaO thermochemical storage system – Experimental investigation of discharge operation modes in lab scale and corresponding conceptual process design

“…Cycle stability has first been proven by Rosemary for 1171 cycles [21]. Kinetic equations for the de-and rehydration have been derived by several authors [22][23][24] and the development of simulation models is still ongoing [25,26]. Other groups focus on the modification of the material in order to enhance the reaction rate [27], adapt the reaction temperatures [28], or to encapsulate the storage material in a permeable shell [29].…”

Multi-physical continuum models of thermochemical heat storage and transformation in porous media and powder beds—A review

“…It has been found, e.g., that equilibrium reaction models lead to an overestimation of reactor performance [112]. In other contexts it was highlighted that the exact reaction kinetics strongly influence the local reaction rate profiles, but do so to a lesser extent for the integral reactor performance [181]. Whereas in some studies it was pointed out that certain physical effects had to be taken into account in order to reproduce experimental data, e.g., a conversion-dependent permeability in [164], others report no significant accuracy loss, e.g., by assuming a constant HTF temperature [187] or entirely neglecting gas flow and advective heat transfer in the reaction bed [205].…”

“…All models rely on assumptions, and models of thermochemical energy storage and heat transformation devices are characterised by a number of typical recurring ones: local thermal equilibrium; the significance of certain heat transport mechanisms like radiation, conduction and advection; constant pressure in the reactive domain; chemical equilibrium; the validity of simplified kinetic models; etc. Some authors set out to clarify the conditions under which these assumptions can be safely made and those under which the assumption better be relaxed in order to obtain physically meaningful results, e.g., [165,179,181,188]. It has been found, e.g., that equilibrium reaction models lead to an overestimation of reactor performance [112].…”

“…Wang et al [89] presented a parallel version of the software used in these previous studies [88,179,181] to enable simulations of more complex systems. The algorithm's performance was assessed using two-and threedimensional examples on up to 240 compute cores.…”

“…As experimentally determined expressions for reaction kinetics can be quite complex and difficult to obtain [180], their importance in engineering scale simulations of directly permeated heat stores was studied in Nagel et al [181]. The study included both monotonic charge-discharge and cyclic buffering-type operation modes and was based on one-and two-dimensional finite element meshes representing an axisymmetric reactor geometry.…”