CIRCULATION AND REDUCTION BEHAVIOR OF IRON-ORE IN A CIRCULATING FLUIDIZED-BED

Hot and cold experiments were carried out as a part of fundamental study for the development of a smelting reduction process. Three kinds of ore with different particle sizes and silica sand were used as the circulation materials. The circulation rate of ore was controlled to keep a constant solid holdup in the cold experiments. On the other hand, for the case of hot experiments the circulation rate of ore was not controlled, and the solid holdup was kept constant by adjusting the whole inventory in the apparatus. The results obtained are as follows: (1) The circulation rate of iron ore increased as the particle size decreased and the average solid holdup in the riser increased. The circulation rate also increased as the gas velocity in the riser increased. (2) The gas velocity and solid holdup were considered to affect the carrying over of particles as driving force and probability, respectively. The ore circulation rate, Gs, was proportional to the product of Fr number and the average solid holdup, (1-epsilonBAR), in the riser. (3) The rate controlling step in the reduction of very fine ore was considered to be chemical reaction. On the other hand, the reduction of larger ore was affected by both chemical reaction and diffusion in the particles.