Characteristics of flight trajectory and heat transfer of liquid steelmaking slag droplet during air quenching granulation process

Air quenching granulation of liquid steel slag is one of the most promising slag treatment technologies, as it effectively utilises the thermal properties of liquid slag while produces value-added slag products. To gain a deeper understanding of this process and explore the flying behaviour and heat transfer solidification characteristics of slag droplets, simulation and experiment on air quenching granulation of liquid steel slag were implemented separately. During this process, the slag droplets fly in parabola along various directions. The greater the slag flow rate is, the greater the resistance to the blowing air and the greater the airflow velocity loss rate are. With the increase of airflow velocity, the loss rate of airflow velocity decreases and the distance of the initial landing point of slag droplets increases. With the increase of nozzle height, the distribution space of air velocity field becomes wider. For the process of heat transfer and solidification of slag droplet, a zone of wake formed on the leeward side. The constant disturbance of the air in the zone of wake formed a vortex and accelerated the cooling of the slag droplet. The cooling rates of five points of the slag droplet are as follows: windward side > upper boundary ≈ lower boundary > leeward side > liquid core. When the particle size of slag droplets decreases from 2 to 0.5 mm, the cooling rate increases from 43 to 320°C/s. The granulation experiment reveals that the cooling process of the liquid slag involves three typical stages: the natural cooling stage before air quenching, the rapid flight cooling stage after air quenching and the cooling stage after slag bead's landing.