Continuously stirred tank reactor for oil-suspended thermochemical energy storage systems for CuSO₄·5H₂O

Abstract

Thermochemical energy storage can be used for heating applications, thereby helping to cut down on greenhouse gases from burning non-renewable fuels by offering a solution for seasonal heat storage. In the scope of the EU project RESTORE, a thermochemical energy storage is used to store low temperature waste heat and use it for district heating. This study presents the thermochemical energy storage as a new continuously stirred tank three-phase suspension reactor for storing heat from renewable sources or waste heat with almost no losses, in reaction. Therefore, the reactor was built of glass, where process parameters, such as the mean residence time, have been varied to obtain optimized results for thermochemical energy storage operating at the fixed temperature of 125 °C chosen due to project restrictions. The heat is used to dehydrate CuSO4·5H2O in the charging step and recovered by rehydrating CuSO4·3H2O or CuSO4·H2O, respectively, while generating heat in the discharging step. Using a mixture of silicone and mineral oil to prevent foaming, conversion rates of over 94 % to CuSO4·H2O were reached in the charging step with the continuously stirred tank reactor, with 1 kW thermal power, 150 mm diameter and 900 mm height in continuous operation. In discharging operation, 100 % conversion from CuSO4·H2O to CuSO4·5H2O was measured. This paper lays the groundwork for a new technology for thermochemical heat storage in low temperature application.