Waste Heat Recovery from Molten Slag via High-Speed Self-Rotation of Particles in the Ultralarge Cyclone

Thermal pollution emanating from molten slag, has become the latest industrial pollution syndrome in the iron and steel industry. Herein, we propose a new slag treatment process based on high-speed particle self-rotation induced by a cyclonic flow field, which intensifies heat transfer from high-temperature slag to the fluid, and demonstrates high heat recovery efficiency in an industrial scale molten slag heat recovery system. In the cyclone, particle self-rotation speeds range from 1200 to 15,000 rpm. Furthermore, machine learning is employed to achieve highly accurate prediction of particle self-rotation speed, with an R2 of 0.989. At the same Reynolds number and with a uniform particle diameter of 5 mm, theoretical calculations indicate that this process reduces energy consumption by 24.1 and 32.1% relative to conventional air blast and water quenching approaches, respectively. Moreover, an ultralarge cyclone was implemented in a 150 t/h industrial-scale molten slag waste heat recovery project, achieving up to 90% heat recovery efficiency. Through the novel process, 1043.3 kg of CO2 emissions can be avoided for every 10 tonnes of molten slag processed, in sharp contrast to the state-of-the-art centrifugal granulation technology, which emits 31.2 kg of CO2 under equivalent conditions. Consequently, an annual reduction of approximately 965,224 GJ in thermal emissions is achieved via the implementation of the cyclone system. This study provides an efficient strategy for mitigating thermal pollution induced by molten slag across the iron and steel industry.