Performance analysis of a gas-solid thermochemical energy storage using numerical and experimental methods

Thermochemical energy storage is not only discussed for the long-term storage of thermal energy with large capacities, but also for applications requiring high specific thermal powers, e.g. the thermal upgrade of waste heat via thermochemical heat transformers in continuous operation. Our work aims at the quantitative analysis of the dominating processes in storage designs for gas-solid reactions, which specifically target high-power applications.

As reference storage design, we chose a 1 kW prototype featuring axial aluminum fins for an increased effective bulk conductivity. It was operated with strontium bromide, which reacts with steam in a reversible gas-solid reaction in the 160–320°C temperature range, reaching specific thermal powers up to 250 W/kg anhydrous salt. By combining our experimental work with numerical studies based on the finite element method, we quantitatively evaluate the influence of the heat transfer-related parameters on the storage's maximum thermal power. Based on a thermal sensitivity study, the largest contributor turns out to be the heat transfer coefficient between the reactive bulk phase and the heat exchanger. The experimentally validated simulation tool allows us to draw further conclusions on the scale-up of the current storage design for large-scale applications. In particular, it provides the necessary data to estimate the exergy efficiency of a broad variety of storage application scenarios of the investigated storage system.