Research On Flight And Heat Transfer Process Of Blast Furnace Slag

Blast furnace slag,which contains a lot of high grade heat,is a by-product in ironmaking process.At present,high temperature slag is mainly processed by water quenching method in industrial production,which not only wastes the high grade sen-sible heat,consumes a lot of fresh water,but also emits harmful gases such as SO₂,H₂S.The dry centrifugal granulation technology overcomes the defects of water quenching method.However,in this process,the granulated slag particles will attach to the wall of the granulated silo when they hit it,which will affect the continuous opera-tion of the granulator and the recycle of waste heat.Therefore,In view of the unclear parameters such as the velocity,falling height,temperature and surface solidification thickness of the molten slag droplets when they impact the wall of the granulated silo,this paper studies the flight and heat transfer process of the molten slag droplets in the granulated silo.In addition,this paper is supported by the national key R&D project(2017YFB0603602-03).The main research contents are as follows:(1)A flight model of blast furnace slag in granulated silo.The flight model of a single slag droplet in the granulation silo was established,and the fourth-order Runge-Kutta method was used to discretely solve the mathematical model established.The influence rules of droplet diameter and initial velocity on the flight process were determined,and parameters such as velocity,flight distance and descent height of the slag droplet were obtained.(2)Numerical simulation of air cooling heat transfer of a single molten slag drop-let.The User-defined-function(UDF)file of air-inlet speed was compiled based on the flying velocity fitting formula of slag droplets obtained above,and the heat transfer process of slag droplets in actual flight was simulated.The effects of droplet diameter,initial droplet velocity and initial air temperature on the thermal characteristics of phase transformation were investigated.The surface temperature and liquid fraction(surface solidification thickness)of the slag droplet under different working conditions were obtained.(3)Experimental study on the flight process of molten slag droplet.In order to verify the effectiveness and reliability of the slag-droplet flight model,the centrifugal granulation experiment platform was built to conduct experiments.Firstly,the effects of the rotational speed of the granulation plate,the diameter of the granulation plate and the flux of the slag on the initial velocity of the droplet were explored.On this ba-sis,the effects of droplet diameter and initial droplet velocity on the drop distance were analyzed,and compared with the theoretical values of the model.In summary,the flying model established and the numerical simulation of heat transfer can obtain the velocity,flight distance,descending height,surface temperature and solidification thickness of the slag droplet during flight.It provides theoretical support for predicting whether the slag droplets are adhered to the pelletizing silo wall and the structural design of the granulation device under different working conditions,which promotes the industrial application of dry centrifugal granulation technology.