SynopsisThe kinetics of reduction of molten iron oxide with CO gas at high temperatures of 1 450 and 1 600 °C were investigated. In order to reduce the influence of mass transfer rate on overall reaction rate of reduction, fine powders of iron oxide were used as specimen and were reduced in a transport reactor. After the specimens of fine powder of reagent grade were melted during falling down in reaction zone, liquid oxide drops thus formed were reduced with CO gas. Mean diameter of liquid particles was 25 pm.The oxide particles were melted and became spherical, and the reduced iron was surrounded by liquid iron oxide. It is assumed that liquid iron oxide always exists on whole spherical surface and the nucleation, growth and cohesion of iron in liquid drop did not influence the overall reaction. The results were analyzed by considering only the mass transfer in a gas film and the chemical reaction at the gas liquid interface.The value of mass transfer coefficient in gas film kg was estimated by using the Ranz-Marshall equation kgd = 2.0+ 0.6Re 1~2Sc 1/3 , D Considering the shrinkage of particles by production of metallic iron, the values of rate constant of chemical reaction k~ were obtained as 19.4 cm/ sec at 1 600 °C and 9.3 cm/sec at 1 450 °C.
SynopsisFor a stable operation of blast furnace and a decrease in fuel rate, the improvement of the qualities of sinter which is the principal charging material is very important. At Wakamatsu Sinter Plant of Nippon Steel Corporation which is equipped with a double-layer charging system, the plant experiment has been made to improve the reducibility of sinter by making uniform and ideal heat pattern in the sintering bed. In this experiment, sinter with excellent properties, 3.7 % FeO, 70 % JIS RI, good hightemperature properties has been manufactured. Findings obtained are summarized as follows:(1) An effective means o f improving the sinter reducibility is to cause porous ore to remain as unmelted ore by lowering the sintering temperature at about 1 250 to 1 300 °C and by increasing the temperature-rise rate in the high-temperature zone.(2) Compact ore should have fine grains to improve the sinter reducibility.(3) The reduction degradation index (RDI) of sinter can be improved by reducing the ratio of A1203JSiO2 in fine raw mix and by lowering the sintering temperature.
The mineral structure of sinter is strongly affected by the heat pattern in the sintering process. For this reason, the control of heat pattern in sintering bed is an important operating factor in the sintering process of iron ore. In the theoretical investigation of sintering process, a simulation model which is considering the coke breeze size distribution, the moisture condensation reaction, the Fe0 formation/reoxidation reaction and other reactions are considered was developed. Many useful findings on an actual sintering operation were obtained from the study of the effects of various operating factors on the heat pattern with the aid of this simulation model.
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