Experimental investigation on granulation characteristics and waste heat recovery of molten slag in gas quenching dry granulation technique

•The breakup mechanism is the interaction of aerodynamic force and inertia force.•The dimensionless diameter empirical formula is derived.•The particle size distributions were mainly concentrated in 1–3 mm.•Waste heat recovery rate is related to particle diameter and fiber mass fraction.•The best airflow velocity is 550 m·s−1 in the gas quenching granulation technique. The gas quenching dry slag granulation technique is one of the most promising slag treatment methods due to realize efficient waste heat recovery as well as high value-added resource utilization. To better understand the granulation characteristics and to achieve high waste heat recovery efficiency in the gas quenching granulation technique, high temperature experiments were performed with different airflow velocity and different molten slag mass flow rate. Particle average diameter, particle size distributions, and fiber mass fraction were in-depth studied for the granulation characteristics. The results indicated that the average diameter decreased with increasing airflow velocity and with decreasing the mass flow rate. The dimensionless diameter empirical formula was presented according to the experimental data. The particle size distributions were mainly concentrated in 1–3 mm. The fiber mass fraction decreased with increasing airflow velocity, but it increased when the airflow velocity exceeds 550 m·s−1 at lower mass flow rate. The higher waste heat recovery rate can be obtained with smaller particle diameter and lower fiber mass fraction. The maximum of waste heat recovery rate can reach 59.55% with the airflow velocity of 550 m·s−1 at the mass flow rates of 4.2 kg·s−1, which is the most ideal working condition.