This project is concerned with the development and experimental testing of an innovative packed bed thermal energy storage (PBTES) system specially designed for waste heat utilization from heavily dust-contaminated high-temperature exhaust gas from steel production. Integrating a PBTES into waste heat recovery systems in the iron and steel industry can provide the necessary flexibility to increase the waste heat utilization rate from the current 45% to up to 97%.
PBTES systems are cost-effective and enable the direct use of dust-contaminated high-temperature exhaust gas as heat transfer fluid. However, the direct utilization of heavily dust-contaminated exhaust gas for charging a PBTES poses several unresolved challenges for which solutions still need to be found. When dust flows through the packed bed during a charging process, it accumulates at the inlet surface of the bed and is not removed again during a subsequent discharging process with clean air. This results in a continuously increasing pressure drop up to complete blockage of the packed bed. A solution for continuous cleaning of the dust deposits is therefore required for continuous long-term operation. Either knocking/trambling mechanisms or continuous regeneration of the contaminated storage material can be used for this purpose. With both methods, however, it is necessary to charge the PBTES from the bottom and discharge it from the top. Normally, however, PBTES systems are charged from the top and discharged from the bottom because this is the optimum operating strategy from a purely thermal point of view (stabilisation of the thermocline, maximisation of thermal efficiency).
In this project, a PBTES with an innovative flow configuration that combines good cleanability with high thermal efficiency is being developed and tested. In this novel design, the storage volume is divided into two concentrically arranged partial volumes. The inner part is charged from the bottom and is therefore mainly responsible for separating the dust (similar to a packed bed filter). The exhaust gas flow emerging from the inner part is diverted by 180° and fed to the outer part of the storage tank. The outer, thermally active part of the storage tank is therefore charged from the top (optimal from a thermal point of view). This concept is being experimentally tested in the project using two test rigs on a laboratory scale and is being prepared for further development into a prototype on an industrial scale. Central aspects of the project are the process engineering design of the concept (storage size, division of the storage volume, optimum geometries, flow velocities, dust separation mechanisms) and the evaluation of the storage technology by analysing experimental data (pressure losses, degradation of the thermocline, energetic/exergetic efficiencies, effectiveness of dust cleaning mechanisms).
Finally, the researched characteristics and key performance indicators of the developed storage technology are used to evaluate its potential for improving the waste heat utilization rate in the iron and steel industry (electric arc furnace) and to raise the technology readiness level of the developed PBTES technology.
