REEXAMINATION OF METHOD OF KINETIC-ANALYSIS ON THE RATE OF STEPWISE REDUCTION OF A SINGLE SINTER PARTICLE WITH CO-CO2-N2 GAS-MIXTURE

In a previous work, single particles of commercial sinter were reduced stepwise with CO-CO2-N2 gas mixtures. In the analysis, the reduction of calcium ferrite (CF) was not taken into consideration. Values of chemical reaction rate constants k(c) and effective diffusivities D(e) in the unreacted-core shrinking model were determined by trial and error so that the calculated reduction curve might agree with the experimental one. In the present work, the method of the kinetic analysis are re-examined: (1) A new method to obtain the rate parameter values in a prescribed way has been developed and the experimental data have been statistically analyzed; values of k(c) and D(e) have been determined so as to minimize the difference area between calculated and experimental reduction curves. (2) Final fractional reduction in the hematite to magnetite stage under rising temperature conditions up to 1 173 K, F'(f), was measured after measuring the one at a predetermined temperature, F(f); below about 1 003 K, CF is hardly reduced and practically F(f) = 0.7 when oxygen reducible in this stage is assumed to be come from hematite and CF. The ratio F(f)/F'(f) is also given as a function of reduction temperature. (3) Some additional experiments on single particle stepwise reduction to the previous work were done in a temperature range from 753 to 1 333 K and rate parameter values have been re-evaluated by the above-stated method in consideration of the facts in (2); temperature dependencies of k(c) and D(e) are presented.