Analysis of a Lab-Scale Heat Transformation Demonstrator Based on a Gas–Solid Reaction

Jana Stengler,Julius Weiss,Marc Linder

doi:10.3390/en12122234

Abstract

Heat transformation based on reversible chemical reactions has gained significant interest due to the high achievable output temperatures. This specific type of chemical heat pump uses a reversible gas–solid reaction, with the back and forward reactions taking place at different temperatures: by running the exothermic discharge reaction at a higher temperature than the endothermic charge reaction, the released heat is thermally upgraded. In this work, we report on the experimental investigation of the hydration reaction of strontium bromide (SrBr2) with regard to its use for heat transformation in the temperature range from 180 °C to 250 °C on a 1 kg scale. The reaction temperature is set by adjusting the pressure of the gaseous reactant. In previous experimental studies, we found the macroscopic and microscopic properties of the solid bulk phase to be subject to considerable changes due to the chemical reaction-. In order to better understand how this affects the thermal discharge performance of a thermochemical reactor, we combine our experimental work with a modelling approach. From the results of the presented studies, we derive design rules and operating parameters for a thermochemical storage module based on SrBr2.

Highlights

Thermochemical reactions, for example reversible reactions between a gas and a solid, have been widely discussed in literature in the context of thermal energy storage
Different thermodynamic heat transformation and chemical heat pump processes have been discussed in the literature, and a number of studies have been published that clearly highlight the potential of heat transformers for the reduction of low-enthalpy waste heat in industrial processes [4,5]
In a previous study based on thermogravimetric experiments performed on a mg scale, we identified strontium bromide (SrBr2 ) as a promising candidate for thermochemical heat transformation [10]

Summary

Introduction

Thermochemical reactions, for example reversible reactions between a gas and a solid, have been widely discussed in literature in the context of thermal energy storage. Compared to latent or sensible energy storage technologies, thermochemical systems offer significantly higher energy storage densities [1] Another key feature of thermochemical energy storage is the possibility to control the charge and discharge temperatures by adjusting the concentration of the reactants: if the gas pressure is increased in a gas–solid reaction system, the reaction temperature rises. This effect can be used to transform thermal energy from a lower temperature level to a higher temperature level, the so-called heat transformation or chemical heat pump [2,3]. Regarding suitable gas–solid reactive couples, there is a broad spectrum of chemical reactions discussed, e.g., ammonia-, hydrogen- or steam-based working pairs, covering a wide range of operating temperatures [9]

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