Facing the challenges of Mine Dewatering

Facing the challenges of Mine Dewatering

Around 280 kilometres north-east outside of Johannesburg lies Mokopane, in the province of Limpopo. The area is one of South Africa's richest agricultural zones, producing wheat, tobacco, cotton, beef, maize, peanuts and citrus. But it is also well-known for its rich minerals such as platinum, diamonds and granite. In Mokopane, you can find the Platreef palladium-platinum-nickel-copper-rhodium-gold mine, which is being developed by Ivanplats, a South African subsidiary of Canadian mining company Ivanhoe Mines. The mine consists of the Flatreef underground deposit, which has a strike length of six kilometres and hosts platinum-group elements, nickel, copper and gold resources. The deposit predominantly lies within the Platreef mineralized sequence at a depth of approximately 700 to 1,100 metres below surface. Water plays a critical role when it comes to mining, e.g. for transporting sludge or suppressing dust. There is either scarcity or the excess of water causing an issue, which is why a reliable dewatering plan is essential. “Each site’s dewatering requirements vary, due to environmental, climatic and geological conditions. Changes in weather conditions can have a significant effect”, explains Clemens Pretorius, Account Manager Water Management at Wilo South Africa. “The dewatering system on site must provide a reliable solution. And this is, where Wilo came into the picture.” Wilo-ACTUN Zetos borehole pumps are used to transfer water from the shaft bottom which is 1000 metres below ground level (b.g.l.), to a pumping station, 950m b.g.l., then to another pumping station, 450m b.g.l., and then finally to the surface.

Offering a turnkey solution

At the shaft bottom, 1000 metres down, Wilo is using its ACTUN Zetos K8, horizontally mounted in a cooling shroud below pontoon. Due to the mining environment, a lot of foreign material such as bolts, nuts and sediment end up in the shaft bottom. By using the pontoon, the water is filtered from these substances and can enter the pump free from solids, which will prolong the lifecycle immensely. The whole system is operated via a direct on-line (DOL)panel, using minimum and maximum level sensors to automatically start and stop. At the 950 metre mark below the groundwater level, water is first delivered from the shaft bottom into a compartment, also known as the sediment trap, inside the holding tank. This way, the sieved water can overflow the tank. It is designed with an outlet to clean the sediment trap of any residue. It also has so-called overflow, drainage and discharge points. The tankis fitted with low- & high-level sensors that communicate with the controlpanel. From this level, water is being transported with Wilo-ACTUN Zetos K10.They are horizontally mounted parallel to the holding tank and connected to it via a suction manifold fitted with isolating valves. The pump systems are connected in parallel so that one pump is always in operation and one on standby. Here, the whole system is monitored and steered via a variable speed(VSD) control panel including the minimum and maximum level sensors. VSD control panels are used to manage ramp-down speed in order to reduce water hammer. As soon as the pumps stop, the water column in the pipeline flows backwards and hits the non-return valves. Water hammer can damage the pump and motor if not managed correctly. The same procedure is used at a level of 450 metres.

“What made this project exceptional to me was, that we could offer a turnkey solution and not only ‘sell’ pumps and motors but offer a complete system solution, designed and sized by Wilo. From pumps, motors and electrical control to gear, tanks, valves etc.”, says Jano Verreynne, Business Developer at Wilo Pumps SA. The system was automated by using Schneider Electric Variable Speed Drives with low- and high-level sensors to stop and start the pumps but also to operate them with their best efficiency. The control gear is incorporated into the mines programmable logic control (PLC) to allow communication with the control rooms. This way, the operator can start and stop the pumps from this room and monitor them. “It was a really interesting project and we are more than proud of it. The fact that Wilo pulled together expertise from all over the world to support us in South Africa and to get the pumps delivered on time was an amazing feeling. It truly made me feel proud to be part of the Wilo team”, states Jano Verreynne.

“Another highlight of this project was the fact that we were contacted in the first week of our local Covid-19 lockdown. We managed to get an offer to them, with all the challenges of not being able to travel or meet in person – the new normal, within two weeks from request.”