Demand of sponge iron and pre-reduced pellets for the manufacture of different varieties of steel is increasing day by day and new solid reductant based sponge iron plants are being commissioned. In the existing blast furnace an increase in production by at least 25 to 35% can be achieved by using pre reduced iron ore. Pre-reduced iron ore pellets have been established as a good substitute for steel scrap in an electric arc furnace which enhances the productivity of the arc furnace. Also majority of fines which are generated during the course of handling, mining, transportation etc are exported at a through away price which need to be utilized by making iron ore pellets for sponge iron making.
A lot of investigations have been carried out on direct reduction process of iron oxides by carbonaceous materials, but little work has been done on the characterization of properties and reduction behavior of iron ore of some mines of Orissa. In the present project work, an attempt has been made to study the reduction behavior and kinetics of fired iron ore pellets. The effect of different reduction parameters such as temperature (850-10000C), time (15-120 min.), reductant quality, pellets Vs lump, mixing of particles of different sizes at different ratios for pellet preparation etc. on the reduction behavior of iron ore pellets. These form the subject matter of the thesis.
First chapter gives the introduction of the subject. It speaks about the need of DRI industry, scope, present status and future planning of DRI industry in India, world wise DRI production, etc. It also presents the mechanism of direct reduction process.
The second chapter shows the literature review.
The third chapter deals with planning of experiments, selection of raw materials, preparation of samples, preparation of iron ore pellets, experimental procedure for characterization of different chemical and strength properties of the selected iron ore lump, proximate analysis of selected noncoking coals, evaluation of reduction and activation energies, study of swelling behavior, evaluation of strength properties of pellets, etc.
The results obtained and the discussions made from these observations have been outlined in chapter four. The result for fired iron ore pellets indicated an increase in degree of reduction with increase in reduction temperature (850-10000C). Fired iron ore pellets showed higher degree of reduction of iron ore pellets than iron ore lump. The reduction behavior of iron ore was identical in all the selected coals.. Abnormal swelling was observed at temperature 8500C and 9000C; whereas shrinkage in the pellets was observed at 9500C and 10000C. The reduction kinetics of Zenith iron ore pellets were studied in the temperature range of 850-10000C. None of the data were found to fit to the kinetic models. So the activation energies of all the iron ore – coal combinations were calculated using Integration method. Pellets made from fines of (-100#) 100% + (-18+25#)10% + (-10+16#)% were showing reduction in activation energy as compared to the pellets made from fines of -100#. In all the studied coal size, least activation energy was observed with coal of -6+16# size.
Results obtained from chapter four have been summarized in chapter five. Lastly, these conclusions have been followed by the list of references.
a) The degree of reduction increased with increase in reduction temperature from 850-10000C
b) There was no effect of type of coal on the degree of reduction of iron ore pellets
c) Iron ore lumps were less reducible than their corresponding iron ore pellets.
d) The reduction behavior of iron ore pellets made from fines of different sizes were comparable with pellets made from fines of -100#.
e) At 8500C and 9000C, the iron ore pellets were showing abnormal swelling after reduction, whereas at 9500C and 10000C, shrinkage was observed in the reduced iron ore pellet
