Study On Coal-based Direct Reduction Of Pre-reduction Pellet Heated By Microwave

In recent years, short flow steelmaking has been rapid development in the world, Raw Material of this process is mainly scrap steel, but scrap steel is shortage in China, so that the development of high-quality substitutes sponge iron to replace scrap steel is very important. Oxide pellets need fast and efficient heating to reduction. In traditional heating reactor, materials heating rely on conduction and convection, can easily cause non-uniform heating of pellets, pellets bond between the surface and the reaction rate was limited.Microwave heating has characteristics of high efficiency energy saving, Energy calculations of coal-based direct reduction heated by microwave show that:energy consumption per tonne of sponge iron for the 3.04GJ,the consumption of coal is 654.44kg when C/Fe=0.531. Microwave energy can be reduced significantly when pre-reduction pellets were used. When the metallization rate of pre-reduction pellet is 42.8% the required microwave energy for direct reduction is only 32% of direct reduction of oxidized pellet.Different from conventional heating.Absorbing material can be heated selectively.The material have strong absorption ability can be heated to high temperatures Priority. Heating experiment in industrial microwave oven show that:heating rate of pre-reduction pellets reduced with the increase of it's metallization, the calculation of its dielectric constant also confirmed the above results. When the metallization rate of pre-reduction pellet is 42.8%, the apparent heating rate of it is 0.332 K/s. heating rate of carbon reductant with small particle size is several times of large one and it can be heated to high temperatures Priority and formation of high-temperature hot spots.In the Shaft Furnace, the mixture of pre-reduction pellets and reducing agent are heated by the microwave,we found that the heating rate in the low temperature phase is different from it in high temperature reaction:in the low temperature the heating rate of mixture is mainly affected by the microwave input power and the granularity of reducing agent, the higher microwave input power and level of fine, the faster heating rate of the mixture; In the high temperature stage, the heating rate ofmixture is affected by the microwave input power and the type and amount of reducing agent. The higher the microwave input power and the reducing agent amount and impurities, the faster heating rate of mixture. Metallization of pre-reduction pellets has little effect on the heating rate because of the existence of fine-level reducing agent and reduction reaction.Pre-reduction can be reduction rapidly under the microwave irradiation, good reduction effects can be achieved in a short period. Mix the pre-reduction pellet with metallization rate of 42.85% and fine pulverized coal,keep the mixture stay in 1000～1050℃, reduction time is 63min, metallization rate of reduction products reached 98.75%. Study on coal-based direct reduction of pre-reduction pellet heated by microwave in the shaft furnace show that:the higher the metallization rate of pre-reduction petllet, the higher the metallization rate of metallization rate of reduction products, but the increased range reduced when the metallization rate of pre-reduction petllet exceed 27.5%.Study direct reduction products by optical microscope, results showed that:spherical mixture of FeO and Fe3O4 were distribution inside the pellet When the metallization rate of pre-reduction pellet is low, reduction was start from the particle surface to inside; fractured mixture of FeO and Fe3O4 were appeared when the metallization rate of pre-reduction pellet increased, CO can easily deoxidize internal oxide.