Water Surface Tension and it’s Effect on Sintering: A Practical Experience in Bokaro Steel Plant

Abstract

Balling is the single most critical factor controlling iron ore sintering process, as it increases mean size of raw sinter mix and permeability. Water is added as binder whose amount & properties greatly influence balling. Surface tension of water is a unique characteristic, which is a necessary evil as regards to balling. One side, it acts positively to form capillary bridges and help in balling. On the other side, it restricts water to get well dispersed among layers of fines, as quickly as required during balling. RDCIS has developed a novel method to optimally reduce surface tension of balling water, by passing it through a magnetic field. A water molecule is typically dipolar, with dipole moment as high as 1.85 D. Hence, water molecules get preferentially oriented towards external magnetic field, which causes reduction in covalent bond angle than 104.45o and subsequent reduction in surface tension. However, being this reorientation a temporary phenomenon (depending on temperature, purity and flow of water), location and intensity of magnetic field was critically designed to achieve surface tension reduction by 16.92%. Enhanced dispersion of balling water thus achieved, has benefitted balling (9% increase in balling index). So both sinter machine speed and air-filtration velocity increased (11.35% & 17.9% respectively). Stronger balls resulted into lesser fines generation too (7.9% reduction in -5 mm content). In addition, the innovation resulted to a reduction in specific solid fuel reduction by 2.24 kg/ton.