Study On Gas-based Reduction And Accompanying Swelling Behavior Of Iron Ore Pellets

With the progress of domestic coal gas technology and mineral separation technology, as well as abundant non-coking resources, the development of coal gasification shaft furnace direct reduction process based on demestic resources characteristics has become a feasible scheme. Therefore, in this paper, reduction of iron ore pellets was carried out by simulating the atmosphere of typical coal gasification gas at different temperatures, using the oxidized pellets made of domestic iron ore. The main innovations and conclusions are as follows:The reduction rate increased obviously with the increase of H2ratio in reducing gas at the same temperatures. The maximum swelling value was obtained for pellets25%～30%reduced with the gas of94%CO. The swelling peaked when the reduction degree reached about40%and then decreased to be stable finally using the gases of H2/CO=1.0、1.6and94%H2. A downward trend in the maximum swelling was observed as the H2ratio increased. As the temperature increase, the increase in swelling mainly comes from the reduction stage of magnetite to wustite. The swelling had a reducing trend with increasing content of hydrogen at the stage of hematite to magnetite. Iron whisker has a higher capacity to contract than cone-shaped crystal.The reduction kinetics of the oxidized pellets reduced by coal gas was studied. The results show that gas-based reduction of iron ore pellets was carried out by outside-in approach, which means the whole process obeys "unreacted core model". The reaction process with the gas of H2/CO=1.0,1.6and94%H2-3%CO2-3%N2obeys interface-chemical model when the temperature between800℃and900℃. In this model, the metallic iron is generated in the form of iron whisker which is likely to contract along with the reduction. However, it obeys mixed model between the interface-chemical and internal diffusion at1000℃, and the metallic iron is created in the form of short and thick cone crystal which is not likely to contract. The reaction process with the gas of94%CO-3%CO2-3%N2obeys mixed model between the interface-chemical and internal diffusion when the temperature between800℃and900℃, while it obeys interface-chemical model at1000℃, and the metallic iron is created in the form of short and thick cone crystal.It is found that swelling is not caused by the formation of iron whisker at various gas atmospheres. The swelling value was increased with temperature increased, which mainly come from volume increase of middle zone in pellets, at the same time grains of core zone were disintegrated gradually serious. The carbon content of pellets reduced with CO was considerably higher, and it decreased with the increase of H2ratio. Black carbon deposited in pellet outer layer fell into fine pores and cracks, which led to an increase in volume. The difference between outer zone and core zone in reduction degree of pellets was increased with the increase of H2ratio, which was conductive to the formation of metallic iron shell and contraction of pellets.