Modeling and simulation of dry grinding of coke breeze in rod mills

Limited to less than 5 m in diameter and, as such, no longer found in large-scale circuits, rod mills remain popular in medium- and small-scale plants, primarily owing to their ability to prevent overgrinding. One successful application of rod milling is in size reduction of coke breeze, a material generated from mechanical degradation of coke during handling which is used as solid combustible in iron ore sintering. The work investigates the grinding response of coke breeze in a laboratory rod mill, through experiments conducted with narrow-size feeds under a range of conditions. Data has been described using the size-mass balance model, which demonstrated that coke exhibits non-normalizable breakage response, with an inflexion point at 0.27 mm. The model showed very good ability to predict grinding of different narrow sizes after being fitted form a single test. The validity of the Austin-Klimpel-Luckie scale-up relationship, incorporating an additional correction term for moisture, has then been demonstrated by comparing results from experiments with different rod sizes, mill fillings, interstitial fillings and moisture contents to predictions, with very good agreement. Finally, predictions of product size of an industrial mill operating at different throughputs were also in good agreements to data collected in plant surveys, demonstrating the great potential of the model in optimizing full-scale operations.