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Double deck roller screens are often used in iron ore pelletizing circuits to control the size of green pellets entering the induration furnace. Besides removing fines that would increase the pressure drop in the furnace, they can also improve the permeability of the bed by inducing stratification. In spite of the widespread use of roller screens in industry, very little information exists on the technical literature that allows understanding how design and operating variables affect their performance. The present work uses the Discrete Element Method (DEM) to simulate the effect of throughput, length of the first deck, besides angle and gap of the lower deck, on the efficiency of separation and the degree of stratification of the bed fed to the furnace. It shows that reduction in lower screen gap resulted in a significant reduction in cut-size of the screen and increase in by-pass to the on-size product, with an optimal value of imperfection with the 9.0 mm gap for the conditions studied. Except for the shortest upper deck, containing only seven rolls, increase in number of rolls in the upper deck resulted in only a marginal improvement on the separation performance of the screen, with no ability to further segregate the pellet bed. Increase in throughput resulted in a marginal detrimental effect on the screen separation performance, whereas reduction in lower slope of the lower deck resulted in reduction in by-pass of the screen.

Iron ore pellets are increasingly important in the production of sponge iron using reduction furnaces. The utilization of pellets present advantages over lump ores, increasing productivity, process stability and throughput. Compared to lump ores, pellets present higher resistance to mechanical degradation. Nevertheless, generation of fragments is still regarded as a challenge in operation. Fragments from pellets generated inside the furnace are known to have a strong influence on the properties of the reduction gas, creating operational problems such as increase in pressure drop, clustering and loss of efficiency. This work studies the influence of the mechanical degradation of iron ore pellets on the properties of the gas inside a reduction furnace. A numerical simulation methodology is proposed for the prediction of the relationship between the mechanical stressing of the pellet, the creation of fragments due to degradation and the influence of the fragments generated on the velocity and pressure fields of the reduction gas inside the furnace. The simulation methodology is applied to predict operation of an industrial MINIMOD MIDREX furnace. Results show that the proposed methodology presents great potential for the simulation of the reduction process giving useful insights about the behavior of key variables and how they relate to the presence of fragments created due to degradation.

Several tests are normally used to analyze the resistance of rocks and ores to breakage in the mining/aggregate industries. Some of these tests yield results that serve as basis for either simple mathematical expressions or comprehensive models, whereas others are essentially only used to classify a rock or ore in comparison with others. The present work demonstrates that the outcomes of three of these tests, namely the Bond crushability index, the JK Drop Weight Test and the Los Angeles abrasion test, can be predicted from simulations using the discrete element method with polyhedral particles with a particle replacement model. In addition to that, a sensitivity analysis of the predictions for the drop weight test results on the basis of selected simulation variables is analyzed, resulting in recommendation of optimal values. The work demonstrates the validity of the breakage model and its ability to describe outcomes of tests that are recognized to capture different aspects of the breakage response of brittle particulate materials.