Improvement in Designing Dry SAG Mills End Liners - Proposed for Gol-E-Gohar Mine

The effect of shell liners on mill performance has been the subject of various studies, but little known about the effect of dry SAG mills end liners on throughput and grinding efficiency. In particular, in the case of dry Aerofall mill types where it has been claimed that the end liners play a key role in the crushing and grinding actions. This paper experimentally characterizes the role of end liners in dry SAG mills with the objective of obtaining a thorough understanding of the effects of end liners design on the load trajectory and SAG mill performance. It was thought the characterization study will lead to design new end liners which eliminate or reduce the shortcomings of the current liners and improve the comminution efficiency mainly by prolonging liner life. The test works conducted in a scale down mill with a diameter of 1m indicated that conventionally used "deflector" type liners did not provide efficient environment for grinding. Direct observations obtained from the model mill during tests by various visualization techniques, along with simulations using the KMPCDEM software were the main sources of understanding flow behavior of charge inside the mill. In this research, to improve the grinding efficiency, a new design using low profile end liners incorporating radial ribs of proper height was investigated. The special design of model mill made it possible to increase the radial ribs height in steps of 6mm up to 18.5mm. The transparent end of the mill enabled accurate trajectory determination by image analysis. The results indicated that the new lower height profile deflectors and 15.5mm-height (14.5cm in industrial scale) radial ribs improved the mill performance while avoiding excessive pressure drop across the mill and wear on the liner. The image analysis showed that the use of new liners increased the distribution of coarse particles across the mill cross section from 28% to 35%. A new liner design was proposed by decreasing the number of liners in each slice from 5 to 4 pieces. The thickness of the inner head liners reduced from 45cm to 30cm and the outer deflector liners replaced by14.5 cm radial ribs. The distance between the feed and discharge liners increased from the original 115cm to 176cm which increased the effective length of the mill by 53%. The new design reduced the weight and volume of end liners by 9% and 23%, respectively. On account of installation of the new liners in Aerofall SAG mills the throughput increased from 441 to 465 t/h, the product size decreased from 519 to 480 μm and the amount of recycled material from the SAG mill product decreased from 10 to 6%. The most significant improvement was observed in the liner life; an increase of 50 to 200 % in liner life depending on the location of end liners was achieved. The relining time also reduced by 37.5% with the new liners.