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 1200uC. 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.

Mathematical model of direct reduction in multilayer pellets made of metallurgical dust in a rotary hearth furnace

“…With increasingly strict environmental protection policies, the need for suitable technologies to treat metallurgical dust is becoming more and more urgent. Of several dust treating processes now available, the rotary hearth furnace (RHF) process is considered as one of the most effective technologies . After being dried, composite pellets made of metallurgical dust are charged into an RHF.…”

“…Of several dust treating processes now available, the rotary hearth furnace (RHF) process is considered as one of the most effective technologies. [1][2][3] After being dried, composite pellets made of metallurgical dust are charged into an RHF. The pellets are heated in the furnace for approximately 20 min.…”

Estimation of Carbon Dioxide Emissions in Rotary Hearth Furnace Using a Thermodynamic Model

“…There has been extensive work performed on the reduction of iron ore-coal composite pellets and its kinetics in RHF experimentally as well as mathematical modeling. [3][4][5][6][7][8][9][10][11][12][13] But only few work has been reported on modeling of RHF for arriving at energy requirements and CO 2 emission (kg-CO 2 /ton product iron) of RHF process routes like Fastmelt and ITmk3. It is reported that energy consumptions and emissions of CO 2 from RHF are lower than in the blast furnace route.…”

Thermal Strength Characteristics and Mechanism of Iron Ore and Carbon Pellets in the Non-isothermal Reduction Process

“…Qingmin MENG, 1) Rufei WEI, 1) Jiaxin LI, 1,3) Ping WANG, 1) Zhifang GAO, 1,2) Zhanxia DI 1) and Hongming LONG 1,2) * The thermal strength characteristics and mechanism of iron ore and carbon pellets (ICP) in the non-isothermal heating process, including the effect of reducing agent, carbon content and heating rate on the thermal strength, were studied by the on-line test device of thermal strength, combined with the TG/DTG-DTA data, the samples microstructure and porosity after reduction. When ICP was damaged by external force at high temperatures, it existed in two states: crush and plastic deformation.…”

“…Iron ore and carbon pellets (ICP), as a new ironmaking raw materials with good reduction properties, provides some possibilities for the new processes development, such as the production of metallized raw materials, the treatment of steel waste containing Fe and the dressing of complex refractory ore. [1][2][3] Many works have been done referring to the reduction mechanism of ICP [4][5][6][7][8][9][10][11][12][13] and the strength of ICP after reduction, 14,15) providing an important support for the development and application of ICP. Jung et al 4) found the critical temperature of carbon gasification was 1 055°C in the carbothermic reduction of magnetite by TGA-DSC-QMS.…”