Thermochemical energy storage with CaO/Ca(OH)2 – Experimental investigation of the thermal capability at low vapor pressures in a lab scale reactor

Abstract

The reversible reaction of calcium hydroxide (Ca(OH)2) to calcium oxide (CaO) and water vapor is well known in the context of thermochemical energy storage. Cheap material costs, a theoretically very high energy density and the potentially wide temperature range of the reaction imply that the storage system could be beneficial for many high temperature processes. For example the system could be applied to store and reutilize industrial waste heat or as an alternative storage solution in future concentrated solar power plants.In this publication the reaction is experimentally investigated in an indirectly operated fixed bed reactor at different technically relevant but so far not investigated operating conditions. This in particular means the thermal charging and discharging of the storage at low water vapor pressures under different heating and cooling loads induced by a heat transfer fluid. The experiments revealed that the reaction gas handling not only affects the operating range of the storage but has also a significant influence on its thermal capability. Especially at low vapor pressures operational limits of the system have been identified and could be contributed to the effective reaction rate of the reaction material which is in the relevant operating range very sensitive to small changes of the local reaction conditions.