Development of a simulation tool for a pebble heaters as part of energy savings and decarbonization of steel plants

Abstract

Steel production is a very energy-and-emission-intensive process, and with its projected increase in the future, due to steel’s vitality in the operation, sustenance, and development of modern economies, there is a huge need for solutions, pathways, and methodologies to increase the sustainability of steel making processes across all production facets, to meet global energy and climate goals. Pebble bed heaters/ Thermal Energy Storage (TES) systems possess great potential to be used as regenerators to recover waste heat across all facets of steel plants. Thus, this thesis focuses on the development of a simulation tool for pebble heaters via numerical modelling of heat transfer and its paraphernalia within packed bed TES systems, as a preliminary instrument for testing use cases and optimizing design decisions for their incorporation in ArcelorMittal’s steel production processes, to ultimately enable energy savings and decarbonization. The project was carried out by executing a thorough literature review and survey on heat transfer modelling techniques of packed-bed heat storage devices used in heavy industries and afterwards, developing a more robust model as an improvement to the previously existing one in ArcelorMittal. The finally developed model was a 1D, twoequation model, numerically computed using the finite difference method with an implicit time integration scheme. The model was verified and also validated using experimental data reported from literature sources. A percentage wise sensitivity analysis executed using the model revealed the importance of optimising the specific heat capacity of the solid particles, the height of the pebble heater and the charging time, to maximize energy extraction from the waste heat source. The diameter of the solid particles was also shown to impact the effective thermal conductivity of the TES system (due to its direct proportionality to the radiative contribution of the thermal conductivity), while also influencing the pressure drop across the system. Finally, some proposals were made for further improvement of the model within the model robustness scope, and a few future activities surrounding the thesis timelines were aptly mentioned.