| Composite Agglomeration Process (CAP) is an innovative technology invented by Central South University, based on the study of ironmaking raw materials and blast furnace ironmaking materials in China. The new process has been successfully put into practice in Baotou Iron and Steel Corp and other enterprises to solve the issues of agglomeration of refractory iron ores, the increase of production and decrease of energy consumption and emissions are achieved, which made great economic and social benefits. In this paper, the pneumatics and mineralization behavior of CAP were investigated.The effect of pellet on permeability is studied by simulating the mixture of CAP. And the reason of pellet improve the permeability is elucidated based on the calculations of pneumatics of bed. The result shows that the permeability of CAP mixture improved with the increase of pellet proportion, and the permeability can be increased by 20%～30% when the materials contained 30%～40% pellet. However, when the fine-grained sinter mixture(0～3mm) exceeds 50% and the size of pellet is greater than 8mm, the permeability increases in the first period and then decreases. Water can improve the permeability of CAP mixture. The mechanism of the improvement the permeability is that pellet can increase the average diameters and porosity of CAP mixture.Effects of roasting time, roasting temperature and oxygen content on the compression strength of different type iron ores are studied through simulation the roasting process of CAP. And indurations mechanism of pellet in CAP is revealed based on microstructure analysis. The result shows that the influence of roasting time and temperature on the strength is obvious, but oxygen content is relatively small under oxidation atmosphere conditions. With the extension of time, the compression strength increases at low temperature(1250～1300℃),while the strength increases in first period but decreases with the time at high temperature(1350～1400℃).The compression strength of magnetite and fluoric iron pellet can reach 2000N/pellet, while the hematite/magnetite mixed iron pellet and the specularite iron pellet can reach 1300N/pellet, 1500N/pellet separately when roasted for 2-3min at high temperature(>1350℃).It illustrate that pellet can get high strength in CAP.The microstructure analysis shows that both the magnetite and fluoric iron pellet are double-layer structure. The external of pellets mainly indurate through recrystallization of Fe2O3 and the internal is mainly in recrystallization of Fe3O4. The hematite/magnetite iron pellet and the specularite iron pellet indurate through recrystallization of Fe2O3. The indurate of pellets external is beneficial for the generation of calcium ferrite, which forms an integral microstructure and ensures high basicity matrix and the strength of CAP product.The CAP tests were conducted in a laboratory sinter pot (φ100mmx500mm). With the tests, the effects of pellet and the mechanisms characteristics of CAP product are studied. The permeability result of CAP is almost the same with simulation test. With the increase of pellet proportion, the finished productivity of CAP keeps at 67%-72%, and ISO tumbling index keeps at 46%～50% when the pellet size varies in the hang of 5～12mm. The finished productivity and ISO tumbling index decrease obviously when the pellet exceeds 12mm..Calcium ferrite is the main phase composition of the high basicity matrix in CAP product. And calcium ferrite in the high basicity matrix interweaved with the recrystallized Fe2O3 on the surface of the pellet. The external of pellets mainly indurate through recrystallization of Fe2O3 and the internal is major in recrystallization of Fe3O4, and the recrystallization of pellet is better than in the simulation test. The three structures forming an integral microstructure, and ensures high strength of composite agglomeration product. |
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