Evaluation of a laboratory rod mill when grinding bituminous coal

Laboratory testing was conducted to evaluate the breakage of bituminous coal in a rod mill. A Pittsburgh seam coal, which had been obtained from the product stream of an operating coal cleaning facility, was used as the feed material. This material had an ash value of 6.7% and had been crushed to a nominal -6.35 mm. Grinding tests were carried out on a mono-size (2.38 × 1.68 mm) fraction. The tests were conducted using a 193.5 mm diameter and 245.0 mm long laboratory rod mill, which contained steel rods at a volume loading of 23%. The mill was operated at 70% of critical speed for various grind times. A locked-cycle test was also performed to simulate continuous grinding conditions. The grinding was characterized using the population (or size-mass) balance model. The breakage distribution and rates of breakage were determined from the grinding data. The results indicated first-order breakage. The locked-cycle results indicated that steady state was achieved in several iterations. The simulated results matched the experimental results very well.