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In a recent study by the authors, green pellets motion behavior and interactions among themselves and with the equipment during classification were successfully modeled through simulations with the discrete element method using the Hertz-Mindlin with JKR contact model. The present work initially deals with a parametric simulation study of five important variables in a roller screening operation, namely, gap between the rolls for removal of undersize, rolls rotational frequency, rolls diameter, deck angle, and throughput. The effect of the individual variables and their interactions are analyzed through factorial simulation experiments. Following these initial simulations, a response surface methodology coupled to the application of multiobjective optimization was used to identify a setting of the various variables that would allow improving classification performance. Such results led to a proposition of a new configuration for the roller screen, which consisted in a significant reduction in roll diameter and deck slope, an increase in rolls rotational frequency and a reduction in undersize gap. Simulations predicted, for the studied material, an increase in fines removal efficiency from 91.4% for the base case configuration to 97.1% for the optimized case, with a reduction to one-third the contamination of the on-size material, and a moderate increase in the efficiency of properly sized material reporting to the on-size product. Although at the expense of a modest increase in loss of properly sized pellets to the oversize, such optimized configuration is also predicted to be significantly more robust to surges in the feed than the base case. [ABSTRACT FROM AUTHOR]

Several approaches have been proposed over the years that may be used to predict the performance of industrial rod mills. Unfortunately, studies that allow comparing the accuracy in their predictions are very scarce. The work compares four methods for predicting size reduction in an industrial rod mill. These were the Bond work index method (BW) and the Callcott–Lynch (CL) model, both originally proposed for rod mills, besides the Herbst–Fuerstenau (HF) and the Austin–Klimpel–Luckie (AKL) models, first proposed for ball mills, but here adapted and applied to rod milling. A total of 10 industrial surveys were conducted of the industrial mill in dry grinding of coke breeze, covering operation under a variety of conditions, all of which at lower fillings than commonly used in industry (<15%). Since most conditions surveyed were not within the typical operating range for rod mills, simulations using the Discrete Element Method were used to predict the mill power, used as input in both BW and HF models. At first, the fidelity of methods that allow predicting full-scale mill performance solely from bench-scale information, namely BW, HF, and AKL, is compared. Results showed that they all presented high biases in their estimates of product fineness, with AKL predicting finer products whereas BW and HF predicting coarser products. Using then data from a single industrial survey for model calibration (base case), in addition to the bench-scale test results, a comparison of the four approaches became possible. Taking the absolute deviations between measured and predicted P80 values, it became evident that the HF provided the highest fidelity in the predictions, with mean deviations of 12.8%, AKL with 15.3%, with both BW and CL presenting deviations above 18%. The work thus shows that size-mass balance models that rely on fitting most model parameters from bench-scale tests (HF and AKL) can provide predictions with good confidence when data from an industrial base case are additionally used in fine-tuning the model, even when applied to describing rod milling under unusually low fillings. [ABSTRACT FROM AUTHOR]

High-pressure grinding rolls (HPGR) have increased their popularity in the minerals industry, since their first application in the 1980s for raw material preparation in the cement industry. Recent advances on the technology have been responsible for putting it in a prominent position among comminution processes, with applications that now range from tertiary crushing stages to pressing iron ore concentrates prior to pelletization. This work reviews some of the recent advances in the technology applied to the minerals industry, including efforts toward improvement on roll lifetime, understanding the effect of progressive roll surface wear on machine performance, alternative lateral confinement systems, the phenomenon of skewing and entirely novel machine designs. Such advances, besides recent insights into the equipment operation, are analyzed, whenever possible, with the assistance of advanced simulation tools, in particular, the discrete element method (DEM). [ABSTRACT FROM AUTHOR]