Reduction Of Iron Ore Fines Research Articles

Reduction of iron ore fines by coal fines in a packed bed and fluidized bed apparatus—A comparative study

Reduction of iron ore fines by coal fines in packed and fluidized beds has been studied. The investigation includes study of the kinetic aspects of reduction, carbon and sulfur content of the direct reduced iron (DRI) produced, and metallography of the products. For both processes, the kinetic data fit the first-order reaction model. Reduction in a fluidized bed is much faster than in a packed bed system. In both cases, DRI contains a substantial amount of free carbon at the initial stages of reduction. At the later stages of reduction, the carbon present in the DRI is mainly in the combined state. For identical temperatures and particle sizes, reaction in fluidized bed is much faster compared to that in a packed bed. At any particular degree of reduction, sulfur content in DRI samples produced by fluidized bed reduction is always more than that of DRI samples produced by packed bed reduction. Scanning electron microscopy (SEM) micrographs reveal that metallic whiskers formed during reduction in packed beds only. These whiskers become more prominent at higher temperatures and longer times.

Kinetics of Gaseous Reduction of Iron Ore Fines.

Unsintered beds of blue dust of varying thicknesses were subjected to reduction in flowing reducing gases. The temperature range was 898 to 1123 K for hydrogen reduction and 1073 to 1373 K for reduction by carbon monoxide. Reduction by CO was carried out in two-stages, and only the data of second stage (wustite→iron) were analysed further. Several approaches to data analysis were attempted. The most satisfactory one was to take the slope of the initial linear region of fractional reduction vs. time curve as a measure of rate constant (k). Extrapolation of k vs. bed depth data to hypothetical zero bed depth for H2-reduction and to 0.4 mm depth for CO-reduction allowed determination of chemical rate constants (kc). In kc vs. 1/T plots were not straight lines. This and other anomalous behaviours were attributed to structural changes in the bed during reduction.

Fluidized Bed Reduction of Iron Ore Fines by Coal Fines.

Reduction of iron ore fines by coal fines in a bed fluidized by air has been studied. The investigation includes study of the kinetic aspect of reduction and effect of major process variables. The variables used are time, temperature, coal/ore ratio and air flow rate. The kinetic data of reduction fit the first order reaction model. Within the range of variables studied, an increase in reaction temperature and coal/ore ratio of the reduction mixture result in higher reduction rate, whereas, increase in air flow rate adversely affects the reduction rate. The activation energy for the reduction reaction is found to be about 155 kJ/mol.

Smelting reduction in iron baths

A joint venture between Klöckner‐Werke and CRA was formed to work out the application of coal injection into the iron bath to smelting reduction. In the Hlsmelt process of CRA smelting reduction of prereduced fine ore is to be carried out directly in the iron bath. Post combustion, different coal grades, and metallurgical reactions were investigated in a pilot plant. Reduction of iron ore fines to wustite was tested in laboratory scale.

Reduction of iron ore fines with coal fines by statistical design of experiments.

A study of simultaneous effects of the major processing variables on the extent of reduction of a column of iron ore fines surrounded by coal fines in an externally heated shaft reactor is reported. The variables studied are ore particle size, coal particle size, coal/ore ratio, time, and temperature. Statistically planned series of isothermal experiments have been carried out to quantitatively assess the effects of each of these variables and of their interaction on the extent of reduction. Within the range of the variables studied, use o f computational methods to find the values of each of the variables to obtain the maximum extent of reduction have also been discussed.

The H-iron process

For over 12 years, Hydrocarbon Research Inc., has studied the direct reduction of iron ore fines with hydrogen in fluidized beds, operating at temperatures below 1000°F, and at pressures above 200 psig. In conjunction with Bethlehem Steel Co. a demonstration-scale direct-reduction plant has been put in operation in Trenton, N. J. Experience with this plant has provided information necessary for construction and operation of a commercial direct-reduction facility.