CFD Numerical Simulation And Experimental Study On Centrifugal Granulation Of Molten Slag

Blast furnace slag is the main by-product produced in the process of ironmaking.The heat content of blast furnace slag produced every year in China is equivalent to the calorific value of more than 10 million tons of standard coal.It is the only energy that has not effectively been recovered in the process of blast furnace ironmaking.At present,most of the blast furnace slag is treated by wet granulation process such as OCP process and INBA process.In addition to the drawback that slag heat cannot be recovered,such wet granulation processes also have some disadvantages such as sulfide pollution and water consumption.Centrifugal granulation is a kind of dry slag granulation methods.Compared with the wet process,this method does not need to consume water resources,does not pollute the environment,and can recover slag heat.Moreover,the treated slag can still meet the requirement for subsequent cement production.Thus,it has received wide attention at home and abroad.In this thesis,numerical simulation and cold model simulation studies on the process of dry centrifugal granulation of molten blast furnace slag by spinning cups were carried out.Firstly,a two-dimensional steady-state CFD model describing the spreading process of molten slag on the inner walls of the spinning cup and a threedimensional transient CFD model for the process of slag film breaking into droplets after the slag leaving the edge of the spinning cup were established.The twodimensional steady-state model was used to simulate the flow and spreading behavior of the slag on the spinning cup surface,so as to predict the thickness of molten slag film at the edge of the spinning cup.Taking the liquid film thickness and slag flow rate as input conditions,the three-dimensional transient model was implemented to simulate the process of slag forming liquid ligament and then breaking into droplets after the slag leaving the spinning cup.The combination of the two models can efficiently simulate the whole process of centrifugal granulation by spinning cups.In this study,the effects of key parameters such as slag flow rate,cup spinning speed and spinning cup diameter on the slag film thickness at the edge of the spinning cup were investigated,and the relationship among slag film thickness,liquid ligament diameter and droplet diameter was explored.In addition,a CFD model was also established to simulate the granulation process of a single liquid ligament following Rayleigh disintegration mechanism.An experimental apparatus was set up in the laboratory to simulate the process of disintegration of a single liquid ligament in cold state with water and liquid paraffin as working fluids.The effects of liquid flow rate and ligament diameter on droplet diameter were investigated by CFD simulation and experimental study.Both the results of the numerical simulation and those of the experimental study verify the similarity between ligament disintegration mode of the spinning cup centrifugal granulation with the Rayleigh disintegration mechanism and thus the validity of the CFD models established for the spinning cup dry slag granulation process.Therefore,the mathematical models established in the present thesis work combined with the cold simulation experiments on single liquid ligament disintegration can systematically explore influences of various parameters on the diameter of slag particles produced by the spinning cup centrifugal granulation process,so as to obtain the appropriate spinning cup structure and operation parameters and provide theoretical guidance for the industrial application of the spinning cup centrifugal granulation technology.