African Mining May 2020 | Page 44

• OPERATIONS dropped down the vertical shaft. Temporary skid mounted intermediate pumping stations would be installed at each 400m decline landing. The submersible pumps would then discharge into these stations. The stations would then cascade up to the surface. Possible drawbacks Two main drawbacks exist with this option: 1. Serious lifting gear needs to be installed at the shaft to carry the combined weight of the pumps, power supply cables and piping with a full column of water. 2. The piping and cables will be continually extended as the level drops. This means a lot of activities will be taking place at the shaft on a limited working platform. This makes for very high safety risks, especially when taking into account the pressurised pipes that the team will be working with. Another, perhaps better option, would be to go through the decline shaft. This provides ample space to hang pipes and cables; the pipes are also easily accessible for extensions as the level drops. The cascade system will still be applicable even with this method to keep the line pressure around 40 Bar. With 4 declines available pumps can be installed in each decline to accelerate the dewatering rate. Common intermediate stations would still be used; however, these stations would need to be sized such that they can accommodate the combined flow rate of all the face pumps. This would be the most effective method and all work would be carried out along the roadway. One additional consideration to be made with this option is provisions to manage accidental water resulting from events such as pipe burst. Because the discharge pipes run along the decline, should a pipe burst, a lot of silt will be washed off along the roads and carried along with the water to the lowest point. Recovery from such an event can be a tedious muddy process if not planned for in the dewatering strategy. Previous successful projects Pumpquip has carried out numerous projects such as this for a number of clients. Most recent was at an Implats operation, Marula Platinum Mine, close to Burgersfort in the Mpumalanga province of South Africa. The original scope was to recover the silt settling system underground and to refurbish and optimise the main pump station. On arrival we were requested to recover two declines with numerous interconnecting crosscuts, all “ The cascade system will be applicable even with this method to keep the line pressure around 40 Bar. Leon Louw At Orion Minerals’ Prieska Copper and Zinc project in the Northern Cape province of South Africa, the historic shaft has been submerged for a number of years. 42 • African Mining •May 2020 www. africanmining.co.za