Pressure-drop modelling in the softening and melting test for ferrous burden

© 2020 ISIJ The softening and melting (SM) under load test is routinely conducted to assess the quality of ferrous burden materials and to predict their possible performance in blast furnace. Due to complex phase interactions coupled with chemical reactions at an elevated temperature range (~973 to 1 873 K), the flow dynamics in the test system are quite complex. This study systematically investigates the contraction behaviour and associated pressure drop in a SM test bed for sinter, lump (NBLL, Newman Blend Lump) and a mixture of these two types of ore (21 wt% NBLL + 79 wt% sinter). To quantify the structural changes in a sample bed, interrupted tests at various temperatures were conducted and analysed using both synchrotron X-ray computed tomography (CT) at a lower temperature range (1 273 to 1 473 K) and neutron CT at a higher temperature (1 723 K). It was noted that existing packed bed pressure drop models (Ergun model, 1952, fused bed model, Sugiyama et al., 1980, orifice model, Sugiyama et al., 1980) and modified orifice model, Ichikawa et al., 2015) exhibited divergence in their predictions at higher temperature when the porosity parameter was computed directly from the bed contraction data. To avoid this modelling failure, a growth-decay type porosity-temperature relationship based on extensive SM test data was incorporated in the well-known Ergun equation which estimated reasonable bed pressure drops. Furthermore, a simplified ore specific friction factor model was empirically derived which was also shown to produce reasonable pressure drop predictions for all types of ferrous burden samples.