Eurotherm Seminar #99 Advances in Thermal Energy Storage 1 EUROTHERM99-02-039 Operation modes and process integration of a thermochemical heat storage system based on CaO/Ca(OH) 2 Matthias Schmidt 1 , Christian Roßkopf 2 , Marc Linder 2 , Antje Wörner 2 1 German Aerospace Center (DLR), Linder Hoehe, Köln, Germany, Phone: 49-2203-6014091, Fax: 49- 2203-6014072, e-mail: matthias.schmidt@dlr.de 2 German Aerospace Center (DLR), Pfaffenwaldring 38-40, Stuttgart, Germany 1. Abstract Efficient thermal energy storage systems for high temperatures at reasonable costs are essential for the economic success of concentrated solar power and can increase efficiency through the recovery of waste heat in industrial processes [1]. Due to the good availability at low cost and its favourable temperature range, previous work at DLR focused on the reversible dissociation reaction of calcium hydroxide: ) ( ) ( ) ( ) ( 2 2 g O H s CaO H s OH Ca reaction     In order to investigate the reaction system, a multifunctional test bench as well as an indirectly operated reactor for 25kg Ca(OH) 2 was developed and put into operation at DLR [2]. Based on the performed experiments, the feasibility to store heat with the Ca(OH) 2 / CaO reaction system in a technically relevant scale (up to 10 kW) was demonstrated [3]. The dehydration was performed at 450 °C, while, during the hydration reaction with 1 bar water vapour, a reaction temperature of 500 °C was reached. Besides necessary improvements in the conveyance of the material, integration concepts need to be developed, that allow an efficient operation of the thermal energy storage system. Consequently, the process parameters of the application system as well as possible operation modes of the thermochemical heat storage system must be understood. Particularly the incorporation of the reaction gas in the process is important to reach high overall cycle efficiencies. The partial use of low grade steam (100 °C) from the process, e. g. extracted from a steam turbine cycle, poses a possibility to drive the exothermic hydration reaction at 500°C. Nevertheless to evaluate the benefit of this thermal upgrade the overall application system needs to be taken into account. This presentation will outline experimentally investigated operation characteristics of the Ca(OH) 2 heat storage reactor. Important parameters such as charge and discharge temperatures as well as the corresponding vapour pressures will be determined. An integration concept for a thermochemical storage system in a concentrated solar power plant is derived taking operating conditions of the plant and the storage system into account. Through modelling of the overall system, valuable results are obtained regarding the incorporation of the heat fluxes and the reaction gas as well as their influence on the overall cycle efficiency. Keywords: thermochemical heat storage; moving bed reactor; operation modes