Research On Flight Dynamics,solidification And Heat Transfer Characteristics Of Molten Steel Slag During Air Quenching Process

The resource utilization of steel slag can effectively solve the problems of primary resource consumption,land occupied by solid waste and carbon emissions,which is great significance to the sustainable development of China's steel industry.Based on the high added value of the product and the recovery of waste heat,air quenched granulation is a slag treatment method with significant economic benefits and good application prospects.In this paper,the solidification heat transfer and flight dynamics of molten steel slag during air quenched granulation were studied.The temperature change law and microstructure change during the cooling process of air quenched steel slag have been researched.The influencing factors and mechanism of molten steel slag flow heat transfer during air quenched granulation,the evolution of liquid-solid phase during solidification and the influence of control parameters on the flight trajectory of slag droplets have been clarify in order to provide a theoretical reference for the preparation of steel slag products and efficient recovery of waste heat.The variation of specific heat capacity of steel slag and the latent heat of phase change have been studied by TG-DSC.A mathematical model of the molten slag droplet in flight cooling process has been established and calculated.The results show that the main phases of air quenched steel slag are Ca₂Si O₄ and Ca₂Fe₂O₅ after cooling.The phase change is the main reason for the change of specific heat capacity during cooling,among which the precipitation of Ca₂Fe₂O₅ has a particularly prominent effect on the specific heat capacity.The cooling rate is affected by the change of specific heat capacity under different cooling modes.At a cooling rate of 60 K/s,the slag shows obvious nucleation and recalescence.The solidification heat transfer law of steel slag droplet in the process of air quenching granulation was studied by simulation.The results show that the maximum temperature difference of the slag particles in radial and longitudinal direction respectively is 164 K and 117 K after cooling for 4.45 s when the air velocity is 1 m/s.When the air velocity is 300 m/s,the maximum temperature difference in radial and longitudinal direction of slag particles respectively is 828.9 K and 805.4 K after cooling for 0.53 s.The time between the beginning and the end of solidification was 0.55 s and3.10 s respectively.The flight dynamics of air quenching granulation process of molten steel slag was studied by simulation.The results show that the distance between the air jet and the dispersion of the slag particles increased gradually with the increase of the initial velocity of the air jet(v_o).The radial range of the air jet increased from about 2.5 m to about 5 m with the v_o increased from 350 m/s to 650 m/s.However,the radial distance of the final slag particle landing concentration area tends to increase first and then decrease.the concentration area distribution of steel slag particles landing increased from about 6-9 m to about 7-10 m with the v_o increased from 350 m/s to 400 m/s.the concentration area of steel slag particle landing is distributed in 5-8 m with the v_oincreases to 650 m/s.The increase in the initial velocity of the air leads to a more concentrated distribution of the slag particles in the high temperature.When v_oincreased from 350 m/s to 650 m/s,the radial distribution distance of the slag particles in the high temperature decreases from within 5 m to within 1 m.