Study of reduction behaviour of prefabricated iron ore–graphite/coal composite pellets in rotary hearth furnace

Abstract

In the present study, the reduction kinetics of prefabricated iron ore–graphite/coal composite pellets of different shapes has been studied in a rotary hearth furnace (RHF). Commercial processes involving the RHF such as ITmk3/FASTMET have major problems of low productivity owing to significant heat and mass transfer resistance through the multilayer bed and consequently limited pellet layers over the hearth. In the present investigation, an attempt has been made to improve the heat and mass transfer in such system by increasing the specific surface area of individual pellets. Both the iron ore–graphite and iron ore–coal composite pellets have been reduced in an RHF at a maximum temperature of 1200°C. The ore–coal composite showed much higher degree of reduction (81%) over ore–graphite composite pellets (61%). The tablet shaped pellet with the highest specific surface area displayed a higher degree of reduction than the cylinder or sphere shaped pellets. Although no physical slag metal separation was visible, X-ray diffraction and SEM/EDX of reduced particles indicated separation at the microlevel. Higher amount of reduction and liquid silicate formation for tablet shaped pellets, in comparison with spherical and cylindrical shaped pellets, lay the foundation of a novel process flow scheme involving the use of prefabricated pellets in the RHF.

Keywords:

• Rotary hearth furnace
• Composite pellets
• Reduction kinetics
• Shape of pellets
• Solid state reduction

The authors acknowledge the financial help from the project sponsored by Ministry of Steel, Government of India, to the Steel Technology Center at Indian Institute of Technology Kharagpur, India.