Liquid penetration rate into submerged porous particles: theory, experimental validation and implications for iron ore granulation and sintering

Abstract

A two-stage model has been developed to describe the penetration of liquid into a submerged porous particle. In the first stage liquid flow is driven by capillary pressure and resisted by viscous losses and the pressure of the air trapped inside the pores. This initial flow ceases when the trapped air pressure equals the capillary pressure. In the second stage the pressurized air slowly dissolves and diffuses through the pore liquid into the bulk fluid; this continues until all the air has dissolved. Novel but simple experiments were performed to measure directly the time required for liquid to soak into porous iron ore particles. The trends of the measured penetration times supported the predictions of the model. Quantitatively, however, the model under-predicted the penetration times. This is probably due to the heterogeneous nature of the pore networks in the iron ore particles, which are poorly described by a single, average pore diameter. The results show that the time taken for iron ore particles to saturate with liquid can be of the order of hours—much longer than the typical residence time during drum granulation in sinter plants. This provides a plausible explanation of why some pre-wetted ores require a higher total mixture moisture content to agglomerate satisfactorily than partially dried ores.