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Study on Coal-based Direct Reduction of Pre-reduction Pellet Heated by Microwave

Author: LvLiLi
Tutor: HuangZhuCheng；PengHu
School: Central South University
Course: Iron and steel metallurgy
Keywords: Prereduced pellets Microwave heating Coal-based direct reduction Shaft furnace
CLC: TF55
Type: Master's thesis
Year: 2010
Downloads: 179
Quote: 0
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Abstract

Recent years, short process steelmaking process worldwide has been rapid development, its main raw material is scrap into the furnace, but the scrap shortage of resources in China, therefore the development of high-quality scrap substitutes direct reduced iron process significantly important. The oxide pellets need for efficient heating to achieve rapid restore traditional heating reactor material by conduction and convection heating, pellet likely to cause uneven heating occurs between the surface of the pellet particles bonded chalking reduce restore speed, so that the reaction is restricted. Microwave heating with energy efficient features, coal-based microwave direct reduction of energy consumption theory calculations show that: use of microwave heating method restore energy consumption per tonne of sponge iron 3.04GJ C / Fe = 0.531 raw coal consumption also 654.44kg. Using prereduced pellets for direct reduction can significantly reduce the use of the microwave energy, when the pre-reduction pellets metallization ratio reached 42.8%, and its reducing the consumption of microwave energy only oxide pellets required for direct reduction of 32% of the microwave energy. Unlike conventional heating, microwave heating, microwaves can be \The small industrial microwave heating tests show that: the pre-reduction the temperature increasing rate of the pellets in the microwave field with the increase in metallization ratio small, the above test results are also confirmed by the calculation of its permittivity. Apparent heating rate remains 0.332K / s When the prereduction metallization ratio of 42.85% of the pellets, the reducing agent has a good microwave absorbing properties, the small particle size of the carbonaceous reductant faster heating rate, the heating in the microwave formed in high temperature hot spots, to speed up the carbon gasification reaction, promote direct reduction pellets. Prereduced pellets dosed reductant rate of temperature increase of the mixed material is constantly changing in the shaft furnace, the microwave heating in the low-temperature heating stage and the high-temperature reaction stage has a different heating law: the mixture heating rate at low temperature mainly by the microwave input power and reductant the granularity, the higher the microwave input power, the higher the proportion of fine grade reducing agents Mixture faster the heating rate of the mixture; at high temperatures, the heating rate of the mixture is mainly affected by the amount of the microwave input power and reductant, species the influence of the microwave input power is higher, the reducing agent is used in an amount higher the impurity the more faster the heating rate of the mixture. In both phases due to the fine fraction to a reducing agent and the presence of the reduction reaction, the degree of reduction of prereduced pellets warming little effect on the mix. Prereduced pellets under microwave irradiation can achieve fast restore, restore be achieved within a short period of time. Reduced when the metallization ratio of 42.85% of the pre-reduction pellets by microwave heating, with addition of the fine coal, and the high-temperature reducing time for 63 min, the reduction temperature is 1000 ~ 1050 ℃ product metallization rate reached 98.75%. Prereduced pellets microwave heating the coal-based direct reduction test show that: Along with the prereduced pellets metallization ratio improve, under the same process conditions, the product of the metallization ratio is higher. When the metal ratio is greater than 27.5% prereduced pellets, enhance the magnitude of the metallization ratio decreased. Use of an optical microscope for the prereduction of the microwave heating of the pellets the reduction product directly to the study results showed that: when the the prereduced pellets metallization ratio is low, the float's body and Fe3O4 mixed particles the oval spherical distribution inside the pellet, deep restored from the particle surface; prereduced pellets metallization ratio increases, float's body and Fe3O4 mixed particle fragmentation structure reducing gas CO can be easily restore its interior, reducing effect.

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