KINETICS OF PRE-REDUCTION OF IRON ORE BRIQUETTES USING LOW GRADE FUELS

Abstract

Nowa-days iron is the measure of Economy and Show-viw« of sound footing of any country. Thus the successive developments in the technology of iron production has occurred as to cope-up with the quest of increasing world demand for iron and steel. Because of the limitations of the high grade reserves of iron and good quality of coking costs needed for the iron production in blast furnace, the present day research in blast furnace technology alms mainly at Increasing productivity and decreasing the coke rate. The use of pre- reduced burden in blast furnaces is one such significant development reported In recent years. Many countries e.g. Japan, Canada, U.S.A., etc. have reported highly encouraging results on the use of pre-reduced burdens in the blest furnace on pilot plants as well as commercial scales. But# very little work has been done, in India towards, production and utilisation of pre reduced agglomerates. Indian iron ore reserves are reported to be around 21,140 million tons. Due to the soft nature of Indian iron ores and mechanised mining, huge amounts of iron ore fines are produced. The suitable grade coking coal reserves, are limited to about 15M million tons out of a total of 103,000 million tons of coal. Hence, in order to improve the economics of iron ore mining and smelting operations, the utilization of iron ore fines and low grade fuels are highly desirable. In addition to the above facts, the existing blast furnaces are not able to cope-up with country's requirement$ for iron and steel. These are two ways to increase the production of iron# first by errecttng new blast furnaces and second, to increase the productivity of the existing blast furnaces, Errection of new blast furnaces requires huge amount of capital ,which is a handicap considering the economic situation of our country. Therefore, use of pre-'reduced burden is highly desirable to improve the existing capacity of Indian blast furnaces. This requires to develop a suitable process which can produce pre-reduced agglomera-teet economically, and development of any process requires the study of the thermodynamic and kinetic factors affecting the process. Hence, this investigation hay been undertaken to thoroughly investigate the effect of process variables e.g. temperature of reduction, time of reduction, type. of reductant, etc. on rate of reduction of iron oxide by taking Indian iron ore fines and low grade coke and wood charcoal as redo ct an t s • This dissertation has been divided into four chapters. Chapter I deals with a short reviEw of the literature pertaining to the various factors affecting the rote of pre—reduction and describes the kinetic studies by various workers in the field of solid state (iv) reduction of iron ore by carbon. The advantages of carrying out prey- reduction under Indian conditions and that of under reduced pressure have also been pointed out* ChaptorrII deals with the deteiiQ-description of the materials with the method of their analysis, the experimental set-up and the procedure for conducting the experiments for kinetics studies of pre-reduction of iron ore briquettes. In Chapterriii, the results of the kinetic studies on the pre-'reduction of iron oxide in the briquettes consisting of iron ore fines and stoichiometric, 37. and 5%• excess then stoichiometric amounts of low grade coke and wood charcoal under reduced pressure (0.1 mm of Hg) have been discussed. It has been found that upto about 30% reduction, the reduction reaction is surface -controlled and highly sensitive of temperature. After 30'/ and upto $5'/. reduction, the reduction reaction proceeds in accordance with the semilogarithmic relation-ship r = C log t + X,, where r is the percent reduction, t is the time of reduction, C and X are constants. This be relationship is found toLvalid for both type# of reduc- tents (low grade coke and wood charcoal) at all the percentages (etoiehiometric, 37. and 57. excess than stoichiometric). The activation energy values for briquettes reduced with etoichiometric, 3`f. and 5/. (v) excess then.stoichiometric amounts of low grade coke and wood charcoals are 50.2 1 2.7, 51.4 1.1, t 0.2 1 1.2 0 52.5 ,4 1.19 50.2 + 0.8 and 52,5 1.4 Kcal s/gm. mole respectively. Fron the reported values of activation energy# the diffusion of iron through Fe304 is suggested to be the rate controlling step. Beyond 857. reduction# the relationship r r. C log t + X has been found to be valid, but within the scope of experimental data, exact mechanism could not be elucidated* Chapter-IV summartses the applications of the pre—reduced briquettes in iron and steel—making processes. tt has also been pointed out that the pre-~reduced briquettes should possess sufficient physical strength and should not swell when exposed to high tempereltures. This ,chapter has been concluded with the remark that these pre-reduced briquettes are an excellent feed to improve the productivity of. Indian blast furnace. Further work on the studies of the kinetics of reduction of iron oxide with wood charcoal and low grade coke beyond 85% reduction and preparation of pre—reduced briquettes on pilot plant scale have also been suggested.