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

Hot and cold experiments were carried out as a part of fundamental stu dy for the development of a smelting reduction process. Three kinds of ore with different particle sizes and silica sand were used as the ci rculation materials. The circulation rate of ore was controlled to kee p 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 co ntrolled, and the solid holdup was kept constant by adjusting the whol e inventory in the apparatus. The results obtained are as follows: (1) The circulation rate of iron ore increased as the particle size decre ased and the average solid holdup in the riser increased. The circulat ion rate also increased as the gas velocity in the riser increased. (2 ) The gas velocity and solid holdup were considered to affect the carr ying over of particles as driving force and probability, respectively. The ore circulation rate, Gs, was proportional to the product of Fr n umber and the average solid holdup, (1-epsilonBAR), in the riser. (3) The rate controlling step in the reduction of very fine ore was consid ered to be chemical reaction. On the other hand, the reduction of larg er ore was affected by both chemical reaction and diffusion in the par ticles.