This paper investigated the cooling processes of high temperature slags using SHTT (single hot thermocouple technique) and CFD (computational fluid dynamics) method for the purpose of recovering the waste heat. A series of slags with the CaO/SiO2 ratio of 1.1 and different Al2O3 contents were designed. The Continuous Cooling Transformation diagrams were established, aiming to bridge the gap between slag properties and practical operations. The variation of slag properties during cooling processes, including crystallization ability and glass forming ability, was investigated by SHTT and the results indicated that the variation of Al2O3 content greatly changed the slag properties, which had a great effect on heat recovery of slags. Slags with Al2O3 content 15 wt% had the smallest critical cooling rate, which was suitable for heat extraction. A 3-D model was developed to simulate the natural heat transfer between a slag droplet and the ambient air in this study using CFD package Fluent software. The results indicated that the temperature differences could be more than 100 degrees C between core and surface of slag droplets with 3 mm in diameter. These large temperature differences could cause crystallization inside the slag droplets, which should be considered in the processes of heat recovery. (C) 2014 Elsevier Ltd. All rights reserved.