Influence of Reducing Gas Composition on Disintegration Behavior of Iron Ore Agglomerates

Abstract

H 2 injection through the shaft into blast furnace (BF) is a potential option for a further reduction of CO 2 emission from BF. H 2 promotes reduction reaction of burden materials, but its influence on their reduction disintegration behavior remains unknown in detail. This study has investigated the influence on the iron ore sinter, self-fluxed and acid pellets and specified essential factors governing the reduction disintegration behavior.Mass ratios of particles below 3 mm in size were measured as an index for reduction disintegration (RDI) after the reduction of burden samples applying the gas mixtures of CO-H 2 -CO 2 -N 2 at 823 K. The reduced samples were observed by an optical-microscope and an electron probe micro-analyzer for evaluation of reaction mode. Further, using the measurement results, stress, strain energy and crack area generated during reduction were calculated and formation mechanism of cracks was examined.RDI value of self-fluxed pellet increased under higher H 2 condition (40%N 2 -20%H 2 -10%CO-30%CO 2 ) and reached to 26 mass%. Such an increase was larger than expected from the standard RDI measure without H 2 . Sample observation revealed a fact that reaction mode governed RDI value, that is, disintegration worsened under the reduction with non-topochemical mode. The fact was explained by the calculation as an influence of crack formation and propagation. In a case of reduction with topochemical reaction, cracks generated in a concentric fashion. Meanwhile, reduction with non-topochemical reaction tended to generate cracks in radial direction, which causes pellet chipping and further degradation. Calculated crack areas showed good correlation with RDI values. The Crack area of non-toochemical reaction was more than double than that of topochemical reaction. This result indicates that disintegration does not much progress when crack area is less than the certain limit value, but it proceeds drastically when it exceeded the limit value.

<i>In-situ</i> Evaluation Method for Crack Generation and Propagation Behaviors of Iron Ore Burden during Low Temperature Reduction by Applying Acoustic Emission Method

“…The authors previously reported that the reduction disintegration behavior under high H 2 atmosphere strongly depends on the reaction mode induced by the reduction conditions, and evaluated the relationship between fine generation and calculated crack area during the reduction of sinters and pellets. 19) However, there is a difference in the reduction conditions between the BF and laboratory tests. The fine generation behavior of lump ores in the actual furnace is affected by thermal decrepitation as well as reduction disintegration behavior.…”

Quantitative Evaluation of Reaction Mode and Reduction Disintegration Behavior of Iron Ore Agglomerates during Low Temperature Reduction

“…The authors have examined the mechanism of reduction disintegration behavior of both iron ore sinters and pellets under high H 2 atmosphere and reported the influence of reduction mode on the reduction disintegration behavior. 17) However, the evaluation of reaction mode was only qualitative, and the relation between the reaction mode and reduction disintegration behavior was not clarified in detail. Therefore, the quantitative evaluation of reaction mode and reduction disintegration behavior, and their relation were examined in this study.…”

“…500 ± 1 g of samples were subjected to the reduction test. 17) The samples were first heated up to 823 K in an N 2 gas stream with a flow rate of 15 NL/min and kept for 10 min. Subsequently, the gas was changed to a gas mixture, listed in Table 2, with the same flow rate, and the reduction test was carried out for 10, 20, and 30 min.…”

“…The quantification of reaction mode during reduction was attempted by EPMA in the same way as previously reported for measurement reduction mode index (RMI). 17)…”

“…In the previous study, it was revealed that reduction disintegration is promoted by the shift of reduction mode from topochemical to non-topochemical reaction due to increase in H 2 and CO 2 concentrations. 17) In the present study, a quantitative evaluation of the reduction and disintegration behaviors of the pellets was attempted by introducing Thiele Modulus (ϕ). ϕ has been formulated using parameters such as gas diffusion coefficient and reaction rate, 19) and the analysis methods of ϕ for high temperature reduction of pellets has been reported.…”