Abstract: Aiming at the granulation of slag under gas quenching， the numerical simulations of the slag granulation process under gas quenching is carried out on the basis of experiments. The VOF model is used to track the free interface and the Realizable κ-ε model is used to deal with the turbulent flow. The granulation process of gas-quenched slag is simulated and the mechanism of slag fragmentation is analyzed. The dimensionless local momentum ratio is then further established and the influence factors of slag viscosity and gas-slag local momentum ratio are analyzed. The results showed that there are two forms of slag fragmentation under gas quenching. One is the columnar fragmentation caused by R-T instability， mainly caused by local high pressure zones on the windward and leeward sides of the slag flow. The other is surface liquid film breakage dominated by K-H instability， which is mainly caused by the velocity gradient at the gas-slag interface. The increase of slag viscosity will increase the particle size of the slag and decrease the crushing efficiency. The increase of the local momentum ratio enhances the liquid film fluctuations on the surface of the molten slag， and thereby increase the number of stripped particles， reduce the fragmentation length， and enhance the fragmentation efficiency of the molten slag.

Key words: gas quenching granulation; surface wave; local momentum ratio; numerical simulation; blast furnace slag