Numerical Simulation Of Heat And Moisture Transfer Of Coke In The Drying Process In The Stock Bin

Metallurgical coke used in blast furnaces in iron and steel enterprises accounts for about 85% of total coke consumption and is the main application of coke.Because of the problems of coke production technology(wet coke)and open-air transportation and stacking,the moisture content of coke supplied to iron smelting is generally high,which affects the quality of coke.The existing researches on coke mainly focus on the process flow and heat transfer process,and lack the theoretical guidance of heat and moisture transfer during coke drying in silo.Therefore,based on porous media theory,drying kinetics theory and computational fluid dynamics theory,A mathematical model of coke drying process in the silo was established.The heat and moisture distribution in the silos was studied with the help of CFD numerical simulation platform.Compared the simulated data with the measured data,the maximum error was 29.3%.The findings suggest:(1)After the coke drying process gas enters from the branch pipe in the silo,it radially enters through the small hole in the pipe wall,passes through the coke material layer,reaches the upper part and is drawn away by the exhaust fan.Because of the floating lift and the resistance of the material layer,when the airflow reaches the silo h =1.0 m,the velocity decays to 0,forming the unloading working area,which conforms to the requirement of no dust and smoke.The gas flows upward to the middle of the coke layer,the gas velocity decreases and the velocity dead angle appears around the wall.Affected by the wall and outlet,the gas velocity accelerated and reached a maximum value of 4.54 m / s at the outlet.(2)Coke temperature depends on the heat provided by the gas,so coke temperature and gas temperature distribution law is consistent.The gas temperature decreases gradually from near to far,and the coke gains heat to raise its own temperature.After 5hours of operation,because of the phenomenon of heat imbalance,the gas temperature is always larger than the coke temperature,the maximum temperature difference can reach 30 °C.Through the average temperature of coke layer and the variation of coke temperature in different layers,we can see that the expansion degree of flow field affects the heat transfer effect.(3)The distribution of humidity of coke is coupled with temperature distribution of coke,and the humidity increases gradually from near to far.Where the flow field is expanded more fully and the temperature heat transfer is better,the drying effect is better.This is the result of the coupling of velocity,temperature and humidity.The average moisture content of coke can reach 3.41% in the layer closest to the air outlet.According to the variation curve of coke moisture near the outlet,the drying process of coke can be divided into preheating drying stage and decreasing drying stage.Because of low initial moisture content of coke,constant drying time is short or even non-existent.(4)The influences of air supply mode,air supply temperature and air supply rate on coke drying process in the silo are analyzed.The results show that the drying effect of radial air supply is better than that of axial air supply.The higher the air supply temperature,the more heat transferred to coke,the better the heat exchange and drying effect,However,too high supply air temperature may lead to spontaneous combustion of coke in silo,and too high temperature will lead to equipment failure such as induced draft fan.The increase of air supply rate is to increase air supply speed,convection heat transfer is more intense,but the wind speed is too high,the inner wall of the silo pressure will be greater,may lead to gas leakage,affect the actual production work environment.The above results provide a theoretical basis for optimizing coke drying process,and have guiding significance for reducing energy consumption,adjusting silo structure and operating parameters.