2018 Volume 58 Issue 8 Pages 1413-1419
In the field of ironmaking, there are few in situ non-destructive techniques for systematically evaluating the reduction behaviors of blast furnace (BF) burden materials. The standard method for the evaluation of the reduction disintegration index (RDI) includes low temperature reduction with a constant gas composition at a constant temperature followed by a cold strength test after cooling. During the reduction of iron ore burden in the BF, reduction disintegration proceeds in the course of increasing temperature through crack generation and propagation caused by volume expansion due to the reduction from hematite to magnetite. Acoustic emission (AE) method is an in situ non-destructive technique to evaluate the crack generation and propagation phenomena in various fields. In this study, we first attempted to apply AE method for a detailed in situ observation of BF burden materials by a combinational experiment of reduction disintegration. In the case of single-particle reduction, it was possible to detect AEs without friction between the sample and the waveguide giving rise to noise. Although a large number of AEs were measured during cooling of both sinter and pellet, the AE energy of the sinter was larger than that of the pellet. Furthermore, a significant number of AEs were also detected during heating of lump ore containing larger amount of combined water indicating possibility to evaluate the decrepitation behavior of such ores.
By the packed bed reduction tests, which could evaluate average properties of iron ore burden, it was found that the AE energy attributed to thermal stress observed during cooling was higher than that to reduction degradation. These results suggest that it will be possible to eliminate the influence of crack generation within the iron ore burdens in the cooling stage by applying the in-situ non-destructive evaluation method developed in this study. It is also expected to apply for the quantitative estimation of the reduction disintegration behavior of burdens in the working BF.