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In recent years, the fight against global warming and therefore CO 2 reduction have become the most important issue for humanity. As a result, volatile sources of energy—like wind and solar power—are penetrating the electrical grid and therefore an increased demand on storage capacities is required. At the TU Wien Institute for Energy Systems and Thermodynamics, a Fluidization Based Particle Thermal Energy Storage (FP-TES) working with bulk material as a sensible storage material is developed. In this paper, the concept and an experimental study of the cold test rig is presented. By means of various pressure measurements, a novel concept of particle transport based on advanced fluidization technology without any mechanical transport devices is investigated. Moreover, a mathematical correlation between the pressure gradients and the particle mass flow is found. Overall, the experimental study provides a full proof of concept and functionality of the novel energy storage system. [ABSTRACT FROM AUTHOR]

To enable the exploitation of the industry sectors' huge waste heat potential this study investigates the utilization of packed bed thermal energy storage systems for the waste heat recovery in the iron and steel industry. The main goal is to assess the partial cycle operation of a packed bed thermal energy storage with industrial exhaust gas that is contaminated with high amounts of metal powder. A continuously rising accumulation of powder particles inside the packed bed requires the storage to be charged from the bottom in order to facilitate the removal of powder hold-up. Therefore, investigations focus on the dependency of the thermal performance of the storage on the flow direction of heat transfer fluid during charging/discharging. Exergy efficiency and thermocline degradation are evaluated as key performance indicators for different flow directions of the heat transfer fluid using a lab-scale test rig. Results show that, compared to charging from the top, a slightly faster thermocline degradation occurs for a storage that is charged from the bottom. Still, energy and exergy efficiencies in partial cycle operation are well above 85% and 80% respectively regardless of the heat transfer fluid flow direction. The thermal power rate during discharging is stable between 74% and 93% with respect to the maximum input rate for both charging the storage from the top and from the bottom. All in all, packed bed thermal energy storage systems are found to be suitable for waste heat recovery in industrial processes. Only a marginal deterioration of the thermal performance of the storage has to be expected if the storage is required to be charged from the bottom. • Impact of air flow direction during charging on thermocline degradation is minimal. • Steady state energy and exergy efficiency in forward operation are 90% and 86%. • Steady state energy and exergy efficiency in reverse operation are 85% and 80%. • Deterioration of partial cycle energy efficiency of max. 5% is measured. • Deterioration of partial cycle exergy efficiency of max. 7% is measured. [ABSTRACT FROM AUTHOR]

The waste heat potential from industrial processes is tremendous and if it can be utilized it may significantly contribute to the mitigation of climate change. A packed bed thermal energy storage system is a low-cost storage technology that can be employed to enable the utilization of waste heat from industrial processes. This system can be used to store excess heat and release this energy when it is needed at a later time. To ensure the efficient operation of a packed bed thermal energy storage, its characteristics in standby mode need to be studied in great detail. In the present study, the standby efficiency and thermocline degradation of a lab-scale packed bed thermal energy storage in standby mode is experimentally investigated for different flow directions of the heat transfer fluid during the preceding charging period. Results show that for long standby periods, the standby efficiency is significantly affected by the flow direction of the heat transfer fluid. The maximum entropy generation rate for a 22 h standby process with the flow direction of the heat transfer fluid from the bottom to the top in the preceding charging process is twice as high as for the same process with reversed flow direction. Energy efficiency is 5% higher whilst exergy efficiency is even 18% higher in the process with reversed flow direction. • Standby mode of a packed bed thermal energy storage is experimentally investigated. • Measurement data is processed by second law analysis. • Energy and exergy efficiencies of max. 92% and 83% are measured. • Standby efficiencies depend on the air flow direction in the charging period. • The impact of natural convection on long standby periods is significant. [ABSTRACT FROM AUTHOR]