| Abstract:With the rapid development of the steel industry of China as well as the increasing price of imported iron ore, the iron-making cost of domestic steel companies has also increased due to a serious shortage of self-sufficiency of domestic iron ore. Efficient utilization of a large proportion of iron ore with relatively low price, such as non-traditional resources (e.g. Specularite ore) and secondary sources (e.g. iron-bearing dust), is of great significance for the reduction of iron-making cost as well as energy conservation and emission reduction. However, the existing processes are not capable of utilizing specularite ore and iron-bearing dust in a large scale, due to their properties of low ballability and refractory performance. Composite Agglomeration Process (CAP) is a brand-new process with significant advantages for the agglomeration of iron-bearing materials in terms of refractory iron ore, fine-grained iron ore and secondary resources currently.The sintering capacity of Baosteel has not already met the requirement of feedstock for blast furnace with the expansion of existing BF together with the construction of new BF. Thus, under the current conditions of raw materials source and sintering technology, the research on the application of Composite Agglomeration Process (CAP) to increase the production capacity and improve the quality of sinter is of great significance, for the aims of energy conservation and cost reduction.In this paper, specularite ore and iron-bearing dust derived from Baosteel were used as the main raw material, and the properties in terms of ballability, roasting consolidation performance, and their effects on the sintering performance of ordinary iron ore were investigated. Feasibility and optimal process parameters of CAP for the utilization of high-ratio of specularite ore and iron-bearing dust were examined. Subsequently, effects of pellet and matrix material on the permeability of sintering bed were investigated to interpret its function of increasing productivity, via gas mechanics analysis of sinter bed. Moreover, consolidation and mineralization behaviors of specularite ore were studied, in order to reveal the mechanism of sinter quality improvement by using CAP. The innovations of this study and the main conclusions obtained are as follows:(1) Agglomeration performances of specularite ore and iron-bearing dust were examined and reasons for difficulty in agglomeration were explained. Specularite ore is with smooth surface, compact structure and poor ballability, as well as a higher roasting temperature requirement (more than1280?). As for the pellet production, specularite ore needs pretreatment of60?90min wet ball grinding and three times high-pressure roller grinding, so that the quality indicators of green balls can only meet the basic requirements. The sintering indexes of ordinary iron ore was deteriorated with addition of19.6%specularite ore, and the vertical sintering velocity decreased by5.27mm/min, yield decreased by8.84%, and productivity decreased by0.454t·m-2·h-1. Likewise, with addition of10%iron-bearing dust, vertical sintering velocity dropped by2.22mm/min, and the drum strength decreased by1.79%.(2) The permeability changes of sintering bed were investigated and the mechanism of yield improvement of CAP was proposed. The permeability of the sinter bed increased by20%-30%when the matrix material was mixed with30%?40%pellet material.(3) Consolidation and mineralization behaviors of specularite ore during CAP were studied and the enhancement mechanism of sinter quality revealed. The CAP product possesses better microstructure strength than conventional sinter, which is composed of acidic pellets and high basicity sinter. High-temperature metallurgical properties of the CAP product show that it can be used as a qualified feed for iron-making. Regarding with the matrix material of ordinary iron ore, needle-like calcium ferrite (SFCA) can generate a lot after crystallization resulting in an excellent strength because of its ultra-high alkalinity; as for the pellet material of specularite ore, the consolidation of pellet was promoted due to the formation of secondary Fe2O3with high activity sourced from the decomposition and re-oxidation of the original Fe2O3. In the CAP product, acidic pellets are embedded in the high alkalinity matrix material, both of them are bonded by the liquid phase generated from the high alkalinity matrix material during sintering, and it is mainly constituted of calcium ferrite and hematite, and also a small amount of olivine.(4) CAP for utilization of a high ratio specularite ore and iron-bearing dust was developed. Compared with conventional sintering process, the dosage of specularite ore can be increased from10%to40%, and the iron-bearing dust ratio can be increased to over10%, meanwhile the height of sinter bed could be increased to from700mm to820mm or above. CAP has advantages of increasing production yield and reducing energy consumption, and a feasibility study of this process has been performed in Baosteel and proves that the implement of this process for industrialization is practicable. |
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