Output SEAP September 2012/12Situated 25km from Lephalale in South Africas Limpopo province, the Grootegeluk open-pit mine employs 2000 people, producing 18,8Mtpa nal coal products using a conventional truck and shovel operation. The estimated minable coal reserve is 2800Mt, with a total measured coal resource of 4600Mt, from which semi-soft coking, thermal and metallurgical coal can be produced.Grootegeluk has the worlds largest beneciation complex where 8000 tonnes per hour of run-of-mine (ROM) coal is upgraded in six different plants.Some 14.8Mt of annual production is transported directly to Eskoms Matimba power station on a 7km conveyor belt with 1.5Mtpa of metallurgical coal being sold domestically to the metals and other industries. Grootegeluk also produces 2.5Mtpa of semi-soft coking coal, the bulk of which is railed directly to Mittal, SA, with the remainder making up 1Mtpa of semi-soft coking and thermal coal which is exported or sold domestically.PROJECT OVERVIEWThe two existing 70m Denver thickeners at Grootegeluks GG2 plant were initially constructed to accommodate feed from that site at a duty of 225tph at 7% w/w.Over the last couple of years, additional streams from other plants were added, placing greater demand on the thickeners. The additional streams from plants GG2, 4, 5 and 6 not only increased the operating tonnages, but also contained a signicant amount of nes. As a result of the new feed tonnages and material, a higher occulant dose was needed, resulting in a reduction in underow density and an increase of overow sliming/pulping occurrences.CASE STUDY:GROOTELGELUK PLANT Organisation:Exxaro CoalSite:Grootelgeluk GG2 Plant, near Lephalale, Limpopo, South AfricaYear:2010Application:Coal tailingsChallenge: Retrot within existing feedwell structure Higher throughput increased nes in feedSolution: Vane Feedwell retrot and thickener upgradeResult: Improvements in underow SG, tonnage and overow clarity Increased throughput from49.9% w/w to 53.3% w/w Improved occulation efciencyOutput SEAP September 2012/13All this lead to poor thickener performance, increased down-time, signicant water losses, as well as impacting the slimes dam capacity.GROOTEGELUK THICKENER UPGRADEExxaro Coals Grootegeluk site approached Outotec to assist with improving the performance of one of the thickeners. The newly developed Vane FeedwellTM was put forward as part of an option to resolve the issues affecting the GG2 concentrator. The Vane FeedwellTM components were retrotted to the internals of the existing feedwell and consisted of vanes, a radially sloped shelf and forced dilution - all standard Outotec Vane FeedwellTM design features.The thickener upgrade on the rst 70m thickener at the GG2 mine in April 2010 was planned ahead to coincide with an extended plant shut down. In addition to the Vane FeedwellTM, Outotec also retrotted a new SCD rake drive mechanism, THICKENER AVAILABILITYThickener availability was signicantly improved upon completion of the retrot. Prior to the upgrade, the two existing Denver thickeners were equally accountable for the ROM downtime. After the project completion, the newly retrotted thickener accounted for only 17% of the ROM downtime with the remaining 83% attributed to the existing, unmodied thickener. Prior to the retrot, the old drive was a major cause of thickener downtime and accounted for 30% of all thickener failures. The new Outotec SCD rake drive mechanism has not been the cause of any thickener downtime since installation.THICKENER UNDERFLOW DENSITY AND INCREASED TONNAGESUnderow density has shown amajor difference following the Vane FeedwellTM installation. Previously, the underow density averaged Denver thickener before retrotincluding a new platform and central column. A TurbodilTM for feed dilution and occulant spargers were also installed to improve occulant addition. A new set of thickener rakes, launder weir plates and local control panel were delivered along with instrumentation including, bed mass, bed level and drive torque.Thickener after retrotOutput SEAP September 2012/1449.9% w/w at a feed rate of 225tph. Post retrot, a density of 53.3% w/w was averaged at an increased throughput of 245tph. This implies that not only a higher underow density can be achieved, but that it can be achieved at increased operating tonnages of 8.8%. Again, this highlights the Vane Feedwells ability to smooth out process variability and hence operate across a wider range. The increase in underow density enabled the slimes deposition to be maximised - a very important factor for Exxaro Coal in terms of Grootegeluks operating costs and sustained operation.THICKENER OVERFLOW CLARITYThe overow clarity showed an improvement from 0.5% w/w to 0.2% w/w, highlighting the Vane Feedwells ability to operate with various materials of different liberation (nes) and solid densities, whilst maintaining effective mixing with occulant and subsequent settling within the thickener.The images shown right, clearly demonstrate the signicant difference in the settling zone and overow clarity between the unmodied and newly retrotted thickeners.FLOCCULANT DEMANDWhile occulant dosage was essentially consistent, averaging 18g/t both pre and post installation, the thickener overow clarity, together with the increase in underow density, indicates the improvement in occulation efciency achieved with the Vane FeedwellTM.INCREASED THICKENER AVAILABILITY - MORE STABLE THICKENER OPERATIONThe three main areas of client focus were, availability, underow SGand tonnage. With all three areas showing signicant improvement. Underow density increased from 49.9% w/w to 53.3% w/w, despite a throughput increase from 225 to 245tph (solids loading from0.72t/m2h to 0.78t/m2h). Overow Original Denver ThickenerRetrotted Thickenerclarity improved from 0.5% w/w to 0.2% w/w and availability increased, with no relative density and/or drive related downtimes since the retrot.The project was delivered on time and on budget enabling Exxaro Coal to increase their throughput. Due to the success of the retrot project Exxaro Coal has appointed Outotec to complete the retrot of the second 70m thickener as well as 50m clarier at Grootegeluk in 2012. If you would like more information, click here to contactduncan.wyatt@outotec.com