Change of equivalent layer porosity of pellets along the length of burning conveyor machine

Difficulties in determining the flow resistance of layer of pellets in the burning conveyor type machines during the heat treatment, associated with significant changes in the layer structure due to its shrinkage during the drying process, the low strength of raw pellets, adjustment layer segregation, sintering and melting of pellets, were considered. As a result, flow resistance of pellets layer on conveyor machines greatly exceeds the resistance value which is obtained in laboratory tests of gas dynamics of pellet layer. According to the impact of many factors on the structure of a burnt pellets layer, which can be taken into account only in their cumulative effect, the authors have introduced the concept of an equivalent porosity. As a result of calculating the amount of equivalent porosity with the available literature data and the data obtained in working out the pellets burning technology in a high layer on Kachkanar conveyor machines, a pattern of its distribution along the length of the conveyor machine was revealed. It was established that most significantly the porosity of the layer reduce due to layer shrinkage in the drying zone and cracking of pellets at the outlet of it. The analysis of estimated expressions to determine the gas-dynamic characteristics of the pellets layer helped to get the dependencies that with a sufficient degree of accuracy can be used to calculate the gas-dynamic characteristics of the layer on the conveyor machines considering different porosity. The obtained results can be used in determining the gas dynamic and thermal conditions, providing work of burning conveyor machines with low specific fuel consumption and high quality of the calcined product. © 2017, National University of Science and Technology MISIS. All rights reserved

Oxidation process in iron ore materials at low temperatures

Using methods of physico-chemical analysis (differentially– thermal and mineralogical) helped to study the oxidation process of magnetite (titanium magnetite) on samples from Olhovsk magnetite and Kachkanar titanium magnetite concentrates at low temperatures (200 – 400 °C). Kinetic curves for the studied materials were obtained at different temperatures; they are typical for topochemical processes. Meanings of specific speeds of oxidation of magnetite various size at different temperatures were calculated and sizes of apparent energy of activation of the process were defined. The influence of partial pressure on kinetics of oxidation in gas phase was studied to expose the limiting point of the process of oxidation of magnetite and titanium magnetite. The order of oxidation reaction on oxygen at definite temperatures and the oxidation degree was calculated using graphical methods. The influence of titanium inclusions in magnetite on kinetics of phase change of magnetite–hematite was examined at the temperature interval of 200 – 400 °C, it happens in mixed operational parameters. Then the process comes to diffusive operational parameters. Kinetic principles and the character of oxidation of the studied materials in nonisothermical conditions were defined at different speeds of heating. These results are of some interest and can be used to optimize the low temperature oxidation regimes of iron ore materials on a conveyor roasting machine. © 2017, National University of Science and Technology MISIS. All rights reserved