Study On Strengthen Coal-based Direct Reduction Of Iron Ore Pellets By Microwave Heating

Blast furnace method is more economical and sophisticated methods of iron production after 400 years development;but the drawback is strongly dependent on the metallurgical coke and the coke manufacturing process of serious pollution. The purpose of development non-blast furnace technology is reduce iron and steel process,save energy,and efficient production. So far formed by direct reduction and smelting reduction process based.This paper was studied on iron ore pellets direct reduction in shaft furnace by microwave heating and based on China's abundant coal resources as reducing agent.Rail materials and reducing agents rapid heating and to promote the reduction reaction because of the feature of integrity and selective by microwave heating.Magnetite, hematite, coal and coke are all well microwave absorbing.When use the model of MW-L0316V industrial microwave ovens whit the heating power is 1.3kw, iron ore pellets, coke and coal heating up faster at beginning, the apparent heating rate is 46.85℃·min-1,40.91℃·min-1 and 40.07℃·min-1; Slow heating rate later,the apparent heating rate is 11.59℃·min-1,11.02℃·min-1 and 12.91℃·min-1.In the continuous shaft furnace reactor,whit the heating power is 7.5kw,C/TFe is 0.32,the average apparent heating rate of mixed materials of Pellets and coke is 5.7℃·min-1.Whit the result of reduction of coal-based iron ore pellets by microwave heating:extend the reduction time and increase the reduction temperature of the materials,the metallization of pellet rapidly increasing. When the maximum temperature is 1080℃, the metallization rate is 77.11%.The kinetic conditions improved by coal crushed.When using coal as a reducing agent whit the granularity is-2mm,reduction temperature is 1050℃, reduction time is 120min and carbon-iron conditions is 0.53, the metallization rate of pellet is reached 97.93%.Using pulverized coal as a reducing agent in the reduction reaction is better than coke in this paper, which is due to the fixed carbon of coal is more than coke, more uniform particle size and smaller. The reducing agent particle size is influence on gasification process. The smaller of particle size,the more conducive to the adsorption reaction and the gasification reaction by microwave heating. Improve the ratio of carbon-iron can increase the metallization of the finished pellets,however, the lower carbon-iron ratio (0.32) still can get a relatively high rate of metallization.The metallization of finished pellets is close to the nature of the coal, it is beneficial effect on the reduction by use high volatile coal.With the reduction reaction continuing, a large number of fragments of wustite was produced in the pellets.It is help CO gas into the internal of the wustite to restore when the porosity increased,then connect the metal iron to bridge and reduction reaction can be fully carried out. Metallic iron and slag was occured after the wustite was restored and just some small crystal remain in a little of wustite. The higher of the materials temperature, the greater the reaction rate of carbon and CO2, the relative reduction of carbon gasification capacity increase by mincrowave heating. Kinetics of carbon gasification in a good condition because of crystal structure of wustitie existence. It is promoted the reduction process because of CO gas fast heated and transfered.