Study On The Temperature Rising Behavior And Coal-based Direct Reduction Of Iron Oxides In Microwave Field

With the quickly development of steel industry in the world, the ironmaking process flow which with blast furnace as the dominant is very boom, maturate, high efficiency. Howeve, because of the long flow, biggest financial, high power consumption, nowadays, in the world where coking coal is shortage and expensive, we should development non blast furnace which clear and high efficiency as early as possible, thus the paper comes to study on the temperature rising behavior and coal-based direct reduction of iron oxides in microwave field, in the interest of providing the theoretic guidance for developing the new technique of the coal-based direct reduction of iron oxide pellet heated by microwave.Different from traditional heating, microwave heating uses the dielectric loss and magnetic loss to heat. The result of rising temperature shows:iron and iron oxide powders and briquettes are all good microwave absorbers, and the rising temperature rate of briquettes is quicker than the one of pellets, the rising temperature can be divided to two stages of fore period and late period:quick rising and slow rising. The order of fore period rising temperature rate is:Fe> Fe3O4>FeO >Fe2O3. Fe2O3 powder and briquette rising temperature is very quick in fore period, and is very slow in late period; Fe3O4, FeO and Fe powders and briquettes rising temperature is very quick in fore period, but are all slow in later. Iron oxide pellets and anthracite are both good microwave absorbers, and the rate of anthracite is quicker than iron oxide pellets. To study the temperature rising characteristics under different microwave powers, weights and sizes, the result shows:when microwave input power is 1.3KW and the temperature coming to 1050℃, the rate of the pellets of 160g and 12～16mm is the quickest, using 42 minutes; when microwave input power is 1.3KW and the temperature coming to 1080℃, the rate of the anthracite of 80g and admixture grade is the quickest, using 43 minutes.To study on the influence of gangue on the temperature rising characteristic and the reduction process of Fe2O3 briquettes and iron oxide pellets in microwave field, the result shows: SiO2 and Fe2O3 in briquette absorb microwave with superimposition effect, which results in an increase in the temperature rising rate; the partial thermal stress caused by gangue in pellets results in plenty of cracks, which in favor of the quick reduction.The structures and properties of iron and iron oxides under microwave radiation are analyzed by the SEM. It is revealed that there are the laws of intermigration and grow between grains of iron and iron oxide. When microwave input power is 1.3KW and temperature is 1050℃, the diameter of Fe2O3 grains changes from about 0.25μm to about 1.2μm; when temperature is 650℃, the diameter of Fe3O4 grain change from about 1μm to about 7μm. After microwave radiation, the order of the briquettes compressive strength is: Fe> Fe3O4>FeO>Fe2O3.To test on Fe2O3 briquettes and iron oxide pellets with anthracite heated by microwave, the result of reduction shows: with the rising of end point temperature and C/Fe, the metallization, the metal iron content and total iron content of briquettes and pellets increase.