For mining, water can be both a blessing and a curse, writes Barnabas Mboweni.
Water is an extremely precious resource; necessary for sustaining life itself. No organisation can operate without it. Whether it is a simple corporate office, a factory, a farm, school, even a household, all need water to operate.
For mining however, water can be both a blessing and a curse. In the confines of the man-made underground caves and mining pits, water is continually intruding through fissures, seepage, rain, and even accidental at times from pipe burst and leaks from service lines. At the same time, clean water is required for mining activities such as drilling, cleaning of equipment and other services. After use, this water adds to the already existing burden of undesired water. It then becomes a balancing act of how much water is sent down versus re-use of already existing water in the workings. At the end of the day all that water needs to be removed from the mine. A process, which if not well managed, can result in flooding (a reportable incident to the Department of Mineral Resources (DMR) of the mine and loss of equipment from water damage). All these can compound to a considerable loss of revenue for the business.
As much as it is necessary to remove water from the mine, water it is still necessary to carry out mining activities. With several interventions, there are companies able to provide unique solutions that allow the removal of nuisance water, treating, repurposing and sending it back into the operations. Such careful use of water means that raw water intake from natural resources are reduced, in line with the provisions of environmental water acts and applicable water use licences.
For historic operations that have not been operating for a very long time (for example Orion Minerals’ Prieska Copper and Zink project in the Northern Cape), with water accumulation up to 300m from the surface of the shaft; de-flooding the cave will be one of the critical path activities in the project plan. A thorough inspection of the cave will rely on the timely completion of the mine dewatering activities.
As a starting point, various considerations must be undertaken, most critical of these will be:
- The vertical distance between the highest point discharge line on surface and the lowest point to be pumped underground.
- The rate at which the mine is to be de-flooded (currently expected to be around 1 000 cubic meters per hour; enough to fill an Olympic-size swimming pool in 2.5 hours).
- Available power at the site. These factors will determine the method to be used, discharge pipe sizes, which at a depth of 1 024m, would require a pipe capable of handling over 100 Bar (10MPa) without taking into account any friction head losses through the line. This is close to 100 times the normal atmospheric pressure at sea level (101.325 KPa).
Fortunately, the mine (Prieska) is equipped with both a vertical shaft and a series of declines running all the way to the bottom level of the mine. This allows for a few viable options that can be considered for the dewatering of the mine. The 400m landing stations along the decline also provide the perfect opportunity for intermediate pumping stations to form a cascading system. This can reduce the pumping heads to about 40 Bar per station instead of over 100 Bar from the bottom straight to surface.
First option would be to go through the vertical shaft. This would entail the use of submersible turbine multistage pumps 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.
Two main drawbacks exist with this option:
- 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.
- 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.
“ The cascade system will be applicable even with this method to keep the line pressure around 40 Bar.”
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 totalling to an equivalent of just over 800m of straight decline, all flooded with approximately 9 million litres of water. This operation was carried out using portable submersible slurry pumps to handle the huge volumes of silt that had been washed down with the decline.
The bottleneck was only the main pumping system which could only accommodate a limited flow rate much lower than what could be achieved by the face pumping. The operation was successfully carried out and mining commenced in those declines within a few weeks.
Prior to that Pumpquip had spent over 18 months at Palabora Copper in Limpopo, Phalaborwa. There the scope was initially to recover flooded ends and assist with on-site pump repairs to support the mining teams. In four months, the company had cleared all the flooded declines, developed a dewatering strategy and were looking after the main cascade pumping system.
Pumpquip was also responsible for the provision and repair of all pumps on site required by the mine development teams. From there the contract was extended to include the implementation of the dewatering strategy, operation and maintenance of the dewatering infrastructure. This also entailed the provision and maintenance of suitable pumps for each stage of the mine development process such as face pumping, intermediate, cascade and main pump station. For such a project, some key principles had to be developed and entrenched into the mind of every member of the team. The two most important were: Water shall not be allowed to run for more than 50m on open roads whether controlled or uncontrolled unless reasonably justified and dewatering of development ends shall take priority above all other activities. With these two principles as the prevailing law amongst all the team members, the rest of the work took care of itself.
Pumpquip’s footprint also extends to surface mining where the company offers pit dewatering solutions through the use of mobile, diesel driven, skid or trailer mounted pump units as well as portable submersible units on floats to allow continuous and uninterrupted pumping. On the submersible units the company usually fits level control switches that when the pump reaches the bottom, the unit cuts off.
Should the water return while the unit is in place, it will automatically switch on again and take care of the dewatering with no operator intervention. The company is currently busy with upgrades of a water treatment works pump station with the objective of reducing the energy consumption of the pump station by replacing the existing pump units and controls with a different type of pump arrangement that offers better efficiencies, smaller motors and smarter controls.
|Established in 1988, Pumpquip is a specialist solutions provider in the fluids handling industry. Our vision is to be our clients’ first choice, ‘Fluid Handling’ solutions provider through the consistent development and delivery of water handling solutions that are fit for purpose, cost-effective and meet the highest quality standards. Our skills and field experience enable us to develop tailored solutions to suit the specific needs of the customer. Our interventions are aimed at enabling mining crews to focus on what they do best while we focus on what we do best.|