A Study Of The Reduction Kinetics Of Iron Oxide With H₂-rich Gas

With the increasing global restrictions on greenhouse gases emissions, metallurgy researchers now are paying more attention to the study of hydrogen reduction. However, to achieve the application of hydrogen reduction in Metallurgical Industry, the reaction characteristics and the control methods of hydrogen reduction must be comprehensively understood. So far, although a lot of researches have been made on iron oxides reduction with hydrogen, some special reaction behavior, such as the abnormal fall of the reduction rate with the increasing temperature still has no definite explanations. In addition, there are still some problems need to be resolved, such as the easier sintering of product at high temperature, the easier deposition of carbon when reduced at low temperature with hydrogen-rich gas, the low utilization rate of reducing gas, the large-scale production of hydrogen at low-cost. This paper concentrates on some of the problems mentioned above. From the perspective of structural changes of the product and the kinetics of the reduction with hydrogen, the effect of the reaction conditions on these problems were analyzed.The static reduction processes of Fe₂O₃ powder, Fe3O4 powder, FeO powder and FeO sheet were investigated under isothermal and non-isothermal condition by using the thermo-gravimetric analyzer ?TGA?. The effects of temperature, gas composition, partial pressure and isothermal time on reduction kinetics and mechanism were discussed. The changes of the reaction rate, the reacted fraction and the product sintering were analyzed by using the scanning electron microscopy ?SEM? and X-ray diffraction ?XRD? techniques. And the main conclusions are as follows.The unusual temperature effect that the reduction rate decreased with the increasing temperature was observed both in the reduction of Fe₂O₃ powder and the reduction of Fe3O4 powder. This effect was related to the reduction process of FeO?Fe. The processes of Fe3O4?FeO and FeO?Fe were carried out simultaneously in the reduction of Fe₂O₃ powder above 873K. A big drop of reaction rate was caused by the small addition of CO to hydrogen. The temperature holding process before and after the reduction didn't affect the sintering of product and reaction rate in the reduction with hydrogen bellow 1173K, the sintering only happened in the reduction process.The unusual temperature effect was observed in the reduction of FeO at 933-1073K, and the sintering and denser iron layer were the main causes. The results of isothermal reduction with H₂-Ar showed that the increasing hydrogen partial pressure in H₂-Ar gas caused a drop of the reduced fraction at 973 K-1023 K. The SEM analysis showed that the new iron reduced from the iron oxide aggravated the sintering phenomena and the resistance of the gas diffusion. Carbon deposition existed in the reduction with H₂-CO mixture at 873-973K. The reaction of carbon deposition happened easiest at 873K with 30%H₂+70%CO, and it can be avoided at high temperature.