Numerical investigation of waste heat recovery and process safety enhancement in molten steel slag granulation by CO₂ quenching: Mechanisms, optimization and industrial implications

The metallurgical industry, responsible for significant energy consumption and CO₂ emission, faces critical challenges in achieving green transformation, particularly in the safe treatment of high-temperature molten slag and the recovery of its waste heat. This study presents a novel three-dimensional numerical model that simulates the heat transfer dynamics and flight behavior of steel slag particles during the gas quenching granulation (GQG) process. By using CO₂ as the cooling medium, the model explores the interactions between gas-solid heat exchange, particle motion, and the effect of CO₂ flow rates on particle cooling and distribution. The results reveal that gas-solid heat exchange dominates the heat transfer process, accounting for over 99.8 % of the total. The CO₂ flow rate is the key factor governing both particle cooling and their spatial distribution. Increasing the CO₂ flow rate significantly enhances heat transfer efficiency and reduces particle landing temperature, while the cooling boundary conditions have a limited impact. In addition, this work identifies several critical safety risks associated with the flight and heat transfer processes of molten slag particles, offering optimized engineering solutions to mitigate these risks. The findings provide a comprehensive understanding of the underly mechanisms of heat transfer during slag granulation and propose practical strategies for improving waste heat recovery. This research offers theoretical and engineering insights to advance the industrial application of CO₂-based GQG technology, facilitating a sustainable, safe, and green transformation in the steel industry.