Incorporation of Pebble Crusher Specific Energy Measurements for the Optimisation of SABC Grinding Circuit Throughput at Telfer

Pebble recycle crushing circuit performance at Telfer has historically fallen significantly short of the design product P80 of 12 mm. An investigation was undertaken to evaluate the current pebble crusher circuit performance, quantify the optimum performance achievable with the existing circuit and examine the impact of pebble crusher performance on the overall grinding circuit throughput. The primary objective of this investigation was to develop an operating strategy that could consistently deliver the finest possible pebble crusher product to maximise the overall plant throughput.The pebble crusher specific energy (Wc) was proposed as a key control variable for pebble crusher operation based on the results of plant survey work. Over the range of pebble crusher specific energies encountered at Telfer, a strong linear relationship was found to exist between Wc and the crusher product size. This direct linear relationship between specific energy and crusher product size remained constant regardless of how the change in specific energy was generated, ie through changes to the crusher closed side setting (CSS), feed rate, liner profile or moisture content. Key findings for the Telfer pebble crushing circuit were: each 0.1 kWh/t change in Wc resulted in a 4.9 per cent to 6.0 per cent change in plant throughput, each 1 mm change in pebble crusher CSS resulted in a 2.2 per cent to 2.6 per cent change in plant throughput, and 0.57 tonne of new feed was displaced for each tonne of crushed pebbles recycled to the semi-autogenous grinding (SAG) mill. The presence of an existing 3000 tonne pebble stockpile between the SAG mill and pebble crushers provides an opportunity to manipulate the feed rate to the pebble crushers independently of the SAG mill pebble production rate. This flexibility, along with excess pebble crushing capacity, enables the pebble crusher specific energy to be maximised the majority of the time. Pebble crusher specific energy has subsequently been incorporated as an online crusher control measure to assist in maximising plant throughput.