Reduction Disintegration Behavior of Lump Ore in COREX Shaft Furnace

Abstract

The heavy disintegration of lump ores would produce plenty of small particles in COREX shaft furnace, which would decrease the gas permeability and productivity of the shaft furnace, thus the proportion of lump ores in the burden of COREX shaft furnace is limited to a low level. In this work, the reduction disintegration behavior of lump ore samples was studied by simulating the reduction process of COREX shaft furnace. The influence of temperature, reduction time and gas composition on the reduction disintegration index (RDI -6.3 ) of lump ore samples were also evaluated. The results showed that the disintegration behavior of lump ores in COREX shaft furnace could be generally divided into three steps and the disintegration mainly occurred in the second step, which was in the temperature zone from 450°C to 650°C with low reduction degree. Meanwhile, the RDI -6.3 of lump ore samples all presented the tendency of "inverted V-shape" in the temperature range from 450°C to 650°C under different reduction time. However, the mutual promotion of reduction reaction and carbon deposition reaction (CDR) was attributed to the main reason for the heavy disintegration of lump ores in COREX shaft furnace. In addition, increasing H 2 concentration in reducing gas and rapid reducing at higher temperature would decrease the disintegration degree of lump ores in COREX shaft furnace.

Characterization of Dust Generated during Mechanical Wear of Partially Reduced Iron Ore Pellets

“…This variation in the wear rate (degradation) of iron ore due to reduction has been reported by several researchers . Especially, the significant increase in the disintegration of iron ore in the temperature range of 400–600 °C is well known.…”

“…Especially, the significant increase in the disintegration of iron ore in the temperature range of 400–600 °C is well known. Usually, this is justified by a 15–25% volume expansion during the reduction of hematite to magnetite, which is associated with the structural transformation of a hexagonal hematite to a cubic magnetite . This expansion leads to internal stresses around the reduction region.…”

“…It can lead to higher heat losses and fuel rates . Hence, a lower production efficiency and unstable furnace operation can take place due to generation of dust in a BF process …”

“…Several researchers have investigated the mechanical wear/degradation of partially reduced iron ore, especially iron ore lump and sinter, at varied temperatures and using different compositions of the reduction gas. Generally, the ISO 4696‐1 standard is used to determine the reduction disintegration index (RDI) of iron ore (lump, sinter, and pellets) by isothermally reducing it at 500 °C for 60 min using a gas mixture of 20% CO, 20% CO 2 , 58% N 2 , and 2% H 2 .…”

“…It has been reported that the maximum wear/degradation of iron ore occurs in the temperature range of 400–600 °C, which is associated with the stress concentrations caused by the volume expansion during the reduction of hematite to magnetite . Furthermore, a higher mass percent of particles smaller than 0.5 mm is produced (≈0.8–3 times higher) due to the reduction degradation of iron ore pellets at 550 °C compared to lump ore and sinter .…”