An experimental and CFD study of the iron ore fixed bed structure and its influence on the direct reduction process

Kurzfassung

The current circumstances of global warming, improved energy efficiency, and the higher suitability of Direct Reduced Iron (DRI) in Electric Arc Furnaces (EAF) for steel production necessitate a transition in the iron and steelmaking process from the traditional blast furnace/basic oxygen furnace to the more sustainable and eco-friendly direct reduction process. This reduction can be effectively studied in a fixed bed configuration, which bridges the gap between fundamental investigations on a single pellet and industrial shaft furnaces. While an average porous media model may be used to simulate the fixed bed reactor, this approach fails to account for the impact of intra- and inter-pellet fluid dynamics as well as heat and mass transfer. To accurately represent the geometric structure of iron ore pellet beds, an experimental construction must be accompanied by a particle-resolved CFD model. This article is divided into successive steps. The first step consists in the experimental construction of iron ore beds with different pellet size distributions (10-12.5 mm and 12.5-16 mm) and of the calculation of the bulk bed porosity and radial average bed porosity. The discrete element method (DEM) is further used to computationally reconstruct random packed beds of 0.5 kg industrial pellets based on the experimental data of pellet size distributions. A 3D domain is created using particle position data from the previous step, and pellets and voids are meshed at different refinement levels. Finally, CFD simulations are carried out to investigate the reduction of iron oxide pellets using H2 as a reducing gas in a fixed bed, considering available experimental data for model validation. The effect of three different bed structures on the overall conversion degree of iron ore is examined. This approach allows for successful modeling of a fixed bed using experimental input and investigation into the potential effects of the bed structure on the overall conversion during the direct reduction of the iron ore pellets.