Effect of Temperature on Morphology of Metallic Iron and Formation of Clusters of Iron Ore Pellets
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CTION
DUE to a conjecture of factors such as lack of scrap, process technology maturity, and cost reduction, most of the direct reduction (DR) reactors started to gain market only in the 1970s. Over the years, various technological developments have been made in order to increase productivity and reduce operating costs.[1,2] The main device used to boost productivity was the rising in temperature, which is responsible for improving the reduction kinetics. However, there are restrictions to achieve this temperature increase in furnaces ranging from DR process engineering aspects to the limitations of raw materials.[3,4] In the first case, an increase of oxygen and natural gas injection prior to entry of reducing gases in the reactor is more usual to be practiced. In terms of raw materials limitations, the problem is the sticking phenomenon which is inevitable in some temperatures and reducing conditions. This phenomenon basically consists of sintering iron generated during reduction, sintering the particles, and forming strong clusters. The interaction between reducing atmosphere and temperature on the formation of such clusters has been the subject of many studies[5–9] JEAN PHILIPPE SANTOS GHERARDI DE ALENCAR, Metallurgical Engineer and VALDIRENE GONZAGA DE RESENDE, Doctor, are with the Ferrous Technology Center, Vale S.A., Nova Lima, MG 34000-000, Brazil. Contact e-mails: jeanpga@ gmail.com; [email protected] LUIZ FERNANDO ANDRADE DE CASTRO, Professor, is with the Metallurgical and Materials Department, Federal University of Minas Gerais, Belo Horizonte, MG, Brzazil. Manuscript submitted on July 15, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
and some important findings have been made. One can cite as an example, the effect of H2-enrichment in the atmosphere that tends to form more pores and, moreover, smaller than the formed by CO and hence decreases the clustering index.[5,6] It is also notable that the temperature plays an important role on the resistance of these clusters.[6–9] In this context, on searching for productivity and temperature increase resulting on the formation of clusters and bed permeability damage, a more detailed characterization becomes relevant in order to correlate the temperature with the morphology of the metallic iron and formation of clusters.
II.
EXPERIMENTAL
The materials used in this work were DR pellets industrially produced in Brazil and serpentinite as coating agent. To perform the clustering tests, pellets within the size range of 10–16 mm and having a compressive strength average value of 290 daN were selected. The choice of serpentinite was due to previous work which showed its good behavior at high temperatures.[4] The passing percentage in 0.44 lm of serpentinite is 79.77 pct. Table I shows the chemical analysis of the pellet and the coating material used in the present study. The coating agent solutions were prepared aiming to a density of 1.13 t/m3 and applied to the pellets by immersion method at a dosage of 3.5 kg/t pellet. After immersion, the pellets were drie
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