Numerical investigation of breakup process of molten blast furnace slag through air quenching dry granulation technique

Molten slag is broken up by supersonic air into droplets through the air quenching dry slag granulation technique.The breakup process of blast furnace slag directly determines the droplet diameter and the waste heat recovery.In order to gain deep insight into the granulation mechanism and visualize the breakup process,three-dimensional unsteady numerical simulation based on the k-x based shear stress transport turbulence model was conducted to simulate the transient breakup process of molten slag(k is the turbulent kinetic energy,and x is the specific dissipation rate).The coupled level-set and volume-of-fluid method was utilized to capture the sharp air–liquid interface.The results show that a flat film is formed firstly under the effects of air impingement,recirculation zone and pressure gradients.Then,the axial wave and the spanwise wave appear simultaneously and the film is broken up into ligaments owing to the generation of vortex and hole structure at the intersection of axial trough and spanwise trough.Finally,the ligaments are broken up into droplets owing to Rayleigh–Taylor instability at the air–liquid interface.The droplets smaller than 3.00 mm account for 80%,with the average diameter of 1.95 mm.

Solidification and heat transfer of molten steel slag particles during air quenching process

In order to effectively utilize the resources and energy of molten steel slag,the variation of precipitation phase and specific heat of air quenched steel slag(AQSS)particles during continuous cooling process was investigated by FactSage and thermogravimetry differential scanning calorimetry.The cooling and solidification process of molten AQSS particles was simulated by Fluent.The microstructure changes in AQSS particles in solidification process were analyzed using an ultrahigh temperature laser confocal microscope and a scanning electron microscope.The results indicated that in the cooling process of molten AQSS particles,the precipitation of Ca_(2)Fe_(2)O_(5) resulted in the largest change of specific heat.Under the condition of slow cooling,the cooling rate is more obviously affected by specific heat.When the initial air velocity was 300 m s^(-1),there was the highest temperature difference in AQSS particles during cooling process.What is more,the compactness of the boundary region of AQSS particles was obviously better than that of its central region.