| Due to energy shortage and environmental issues, it become inevitable for the steelindustry to reduce energy consumption as a circular economy. Blast furnace slag is aby-product of the steel industry which has a large amount of waste heat with highrecovery value. But now slag is mainly treated by the method of water quenching whatwastes a large mount of heat and water resources. It which granulate molten slag by thecentrifugal granulation machine and cooling the slag droplet by air stream can not onlyrecycly the heat of slag through the air with better quality slag product but also savewater and reduce pollution.The research on heat transfer characteristics and phasechange of slag droplet cooling by air is significant and guide for the design of wasteheat recovery system. But the cooling of slag droplet by air involves complicated heattransfer processes, in particular, involves the solidification of the molten slag. Thewhole heat transfer processes have complex mechanisms with many influence factors,and the mutual coupling between the various factors brings difficulties in study.Solidification and heat transfer of air-cooling molten blast furnace slag droplet isnumerically simulated by the volume of fluid (VOF) method coupling with thesolidification/melting model.The characteristics of slag droplet heat transfer,solid-liquid interface movement of slag droplet, air flow and temperature field solidifyare explored. The influence of the droplet size, the droplet initial temperature, airvelocity and air temperature are discussed. A model of slag droplets cooled by air wasbuilded based on it. The characteristics of multiple slag droplets heat transfer,solid-liquid interface movement of slag droplet, air flow and temperature field solidifyare explored. The influence of droplet diameter, droplet separation, air velocity andinitial temperature of the molten slag on the air-cooling slag is discussed. A model ofswirling slag droplets cooled by air was builded too. The characteristics of swirling slagdroplets heat transfer, solid-liquid interface movement of slag droplet, air flow andtemperature field solidify are explored. The influence of droplet diameter and swirlingvelocity of the molten slag on the air-cooling slag is discussed. The main conclusions ofthis paper are summarized as follows:①For a single air-cooling slag droplet, the surface of slag is rapidly solidifiedwith internal non-uniform solidification caused by the change of airflow field andthermal conductivity of the solid phase. For the smaller droplet and high air inlet veloctiy, it takes short time for the solidification due to stronge heat transfer on surface.The air inlet temperature has slight influences upon the solidification process of moltenslag droplet. It which raise initial temperature of slag can’t improve waste heat recoverybut takes significantly longer time to completely solidification.②For multiple slag droplets, the distribution of the droplets affect the air velocityfield with heat transfer reinforcement to the front droplet and weaken to the behinddroplet by air backflow. The droplet has more significant influence on others with largerdiameter.The influence between droplets is more obvious with greater air flow veloctiyand smaller interval.It is unfavorable for slag waste heat recovery with a too smallinterval.The coalescence of two droplet is more likely to be happened for droplet withhigher initial temperature.③For a swirling slag droplet, the droplet has greater impact on air flow.Especially100°to135°of the slag surface, air reflow more apparent which brings fastercooling.With larger swirling velocity，the slag droplet is more out of shape and cooledfaster by air in shorter completely solidification time. For the smaller droplet, it takesshort time for the solidification due to stronge heat transfer on surface.④The influence of the molte slag droplet distribution, diameter, separation, airvelocity and initial temperature should be comprehensively taken into account for thedesign of waste heat recovery system. |
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