High temperature thermochemical heat transformation based on SrBr2

Abstract

Currently, state of the art working fluids of conventional heat pumps are limited to maximum output temperatures of 140 °C, and thus cannot fulfill the need for high temperature heat pumps in industrial applications. This is why thermochemical reaction systems have come into the focus of interest: they offer the potential of high temperature energy storage and heat transformation, e.g. by making use of the pressure dependency of a gas-solid reaction. These reactions can in general be described by the following equation: A(s) + B(g) ⇌ AB(s) + ΔRH. Variation of the pressure of the gaseous reactant B results in a temperature shift of the exothermic reaction. In this way, the exothermic reaction (energy output) can be performed at higher temperatures than the endothermic reaction (energy input). In this contribution, the thermodynamic principle of thermally driven heat transformation and its main difference with respect to conventional or sorption based heat pumps is outlined. The scope of this work is the potential of the SrBr2–H2O system as a possible candidate for thermochemical heat transformation. Constraints for a suitable reactor geometry and the possibility to combine thermal upgrade and thermal energy storage into one system are analyzed. Experimental results from a laboratory scale test reactor (~ 1,000 g) support the proof of concept of heat transformation in the region of 200 °C.