Modern Mining January 2016

COAL

innovation at Shondoni

technology to inject grouting via pipes inserted down holes drilled in front of the work area,” said Louw. The shaft inclines at 12 degrees for a dis- tance of 980 m, housing the 3,5 m/s single incline conveyor that will extract 3 200 tons of coal per hour. Coal will be mined mainly from the 4-m thick Number 4 seam at between 140 m and 160 m below surface, by normal bord-and- pillar methods as employed at Middelbult. Continuous miners break the coal and load into shuttle cars, which deliver into feeder breakers; an underground crusher sizes the coal to -150 mm lump size. Section conveyers take product onto trunk conveyors, which in turn deposit it into underground bunkers; coal reports to the incline conveyor from the main underground bunker on Number 4 seam. The 15 000-ton capacity surface bunker – constructed by Stefanutti Stocks Civils – also adopted an interesting approach by using pre- cast ‘planks’ up to 20 tons in weight to facilitate a safe and efficient construction process. Cast in a dedicated precast yard nearby, the compo- nents were placed sequentially by gantry crane and stitched by concreting. “This innovation led to a substantially safer working environment, with much less need for scaffolding and working at height during con- struction,” said Louw. The design went on to be commended at the Concrete Society of Southern Africa’s Fulton Awards 2015, where it was described as an excellent example of hybrid or compos- ite reinforced concrete structures – showing the benefits of precast combined with in-situ concrete. Leading from the bunker is the record- breaking, 21-km-long conveyor. It is reportedly the longest in the world that can run this dis- tance with drives only at the head and tail, an achievement made possible by a more energy- efficient drive system that reduces power consumption. “It must also curve to avoid a settlement and a gold mine tailings dam and must cross roads and waterways,” said Louw. “Environmental concerns also demand that the belt is spill-free and must be sealed when it crosses sensitive areas.” To minimise the environmental impact of the conveyor, it was necessary to prevent

carry-back spillage along the conveyor route. This was addressed by installing belt turn- overs – at head and tail – to rotate the belt 180 degrees as it turned. This ensures that the dirty side of the belt is facing up for both top and bot- tom strands of the conveyor, stopping residual material from falling off the belt as it passes over idlers. The conveyor is covered over its full length to prevent rain from washing coal dust off the belts, and to reduce the propagation of dust and noise; dust suppression sprays at the transfer chutes also help keep coal dust to a minimum. The installed drive capacity on the conveyor is a substantial 5 MW, with four drives at the head and a single drive at the tail. An 80-ton counterweight puts the necessary tension on the belt to prevent slippage at either end. This element of the project will be one of the last to be finalised and will be commissioned in the second half of 2016. Maintenance and monitoring of this ambi- tious conveyor design is clearly vital for smooth

The massive winder house was moved by crane across 58 m and hoisted to a height of over 30 m before finally being positioned on top of the headgear.

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