Isothermal reduction of powdery 2CaO center dot Fe2O3 and CaO center dot Fe2O3 under H-2 atmosphere

Abstract Injection of natural gas into the tuyere raceway of a blast furnace (BF) can effectively decrease the use of coke, as well as reduce CO 2 emission. Therefore, the reduction behaviour of sinters, which account for 60% of the raw materials charged into the BF process under H 2 , is important for natural gas utilisation. This study used thermogravimetric analysis under H 2 atmosphere to investigate the reduction kinetics of dicalcium ferrite (2CaO·Fe 2 O 3 , C 2 F) and calcium ferrite (CaO·Fe 2 O 3 , CF), which are the dominant components in fluxed sinters. Results indicated that CF reduction has a larger maximum reduction degree and a higher reaction constant than C 2 F. The apparent activation energy of CF is also larger than that of C 2 F, thereby illustrating that C 2 F reduction proceeds more easily than CF. X–ray diffraction measurements indicated that C 2 F is reduced to CaO and Fe in a single step, whereas CF is reduced with four steps in the following order: CaO·FeO·Fe 2 O 3 , CaO·3FeO·Fe 2 O 3 , C 2 F and Fe. Sharp and ln–ln methods revealed that C 2 F reduction is described by 2D Avrami–Erofeev (A–E) equation and that of CF is expressed by 2D A–E equation but tends slightly to 3D A–E equation in the late stage. A–E equations were verified to be consistent with the experimental reduction degree data of C 2 F and CF. A kinetics model that links reduction routes to model functions was proposed to describe the powder reduction of C 2 F and CF. Comparisons of the reduction behaviours of C 2 F or CF by H 2 and CO implied that the reduction rate rises and activation energy declines during the reduction of samples by H 2 .