Reduction Behaviors of Pellets under High Reduction Potential

As processes of pure oxygen blast and top gas recycling are applied in the top gas recycling oxygen blast furnace,gas compositions in the furnace are dominated by H₂ and CO,which are quite different from those in traditional blast furnace.In order to study the influence of H₂ and CO on reduction behavior of pellets,experiments were conducted with mixed gas H₂-N₂,CO-N₂ and H₂-CO respectively at 1173K by measuring the weight loss.It is found that the reduction degree increases with the increase in H₂ or CO ratio in the mixed gas,but the reduction with hydrogen is faster than that with carbon monoxide.The increase in hydrogen content in H₂-CO mixture improves the reduction rate while the increase in carbon monoxide in H₂-CO mixture lowers the reduction rate.The reduction rate of pellets under H₂-CO atmosphere can not be simply calculated by adding together the reduction rates under H₂-N₂ and CO-N₂ atmosphere.The result shows that dense structure of iron is obtained in the reduction with hydrogen while the iron falls apart in the reduction with carbon monoxide.As gas mixture containing carbon monoxide was taken as reducing agent,the reduction curve showed a declining trend due to carbon deposition at the later stage of reduction.It is concluded that the existence of H₂ could aggravate the carbon deposition while existence of N₂ could restrain carbon deposition.The results of X-ray diffraction and chemical analysis demonstrate carbon in the reduced sample mainly exits in the form of cementite(Fe₃C) and graphite.