“In most instances, this is the result of higher repair and maintenance costs,” Kruyswijk said. Those costs “may at first seem incidental compared to the cost of replacing the entire system with a single-lift system.” Ultimately, however, when combined with the costs of both planned and unplanned downtime they “undermine the economic viability of the multistage centrifugal dewatering system.”

In some cases, simply improving the existing multistage system is advantageous. In other cases, it can be rebuilt into a single-lift system. “There is almost always room to improve these legacy systems,” Kruyswijk said. “And Weir has the engineering expertise and the product portfolio to assist miners in carrying out the detailed analysis required to determine whether implementing a single-lift system would not only improve the mine’s dewatering operations, but also reduce its operating costs.”

A single-lift system designed around GEHO PD pumps offers a range of benefits, including cost savings and efficiency gains. “A single-lift system basically replaces the core of the multistage system,” Kruyswijk said. “Water is then collected in a central sump, and a single, high-head PD pump pumps it out of the mine in a single lift.”

A single-lift system can use the decline used by the multistage system. “However, the best results are achieved if existing vertical access to the surface is available,” he said. The single-lift system could use existing blind shafts, ventilation shafts, hoisting or manway shafts, or boreholes. “Compared with decline access, which is essentially a system of ramps and crosscuts that connect the access points, shaft access means less piping length is needed to reach the surface, reducing costs and potentially determining the project’s feasibility.”

Using a vertical access, as opposed to a decline access, lowers the head requirements significantly, Kruyswijk said. “Power consumption and carbon emissions are around 30% lower for a single-lift system,” he said. “The higher the flow and the deeper the mine goes, the greater these savings become.”

Single-lift systems require less maintenance. That reduces “the traffic underground and minimizes the amount of time personnel are required to perform potentially risky tasks, like pump rebuilds, in confined spaces,” he said. It also reduces maintenance costs.

Further, GEHO PD pumps offer key advantages over centrifugal pumps. “Firstly, high-head centrifugal dewatering pumps are typically designed to handle clean water, which means that, as the mine gets deeper and there’s an influx of coarse particles, the pump’s wear life is radically reduced and there’s an increased likelihood of pump failure,” Kruyswijk said.

“GEHO PD pumps can handle significantly higher solid concentrates than it encounters in dewatering applications, ensuring greater reliability and pump efficiency,” he said. “GEHO PD pumps can handle slurry concentrations up to 85%, which far exceeds the requirements for dewatering applications.”

Data also shows that GEHO PD pumps are more efficient than their centrifugal competitors, he said. Centrifugal pumps are most efficient at between 75% and 110% of flow. “But if that’s deviated from, then the efficiency drops significantly,” Kruyswijk said. “This can become a challenge in mines that have large operational windows.”

For example, some mines have a large operating flow-rate range due to seasonal water ingress. “In these environments, multistage centrifugal pumping system are often inefficient,” he said.

GEHO PD pumps are “efficient throughout the entire operating envelope,” Kruyswijk said. “From a sustainability perspective, the required head, combined with the efficiency of the pumping system, dictates the power consumption.”

Results vary, but installing a PD pump typically offers “around 20% instant energy cost reductions at the nominal flowrate,” he said. “And during seasonal ingress, these savings can increase to more than 30%.” Thus, as a mine deepens, it is often “cost-effective” to replace complex multistage systems “with a single-lift system, whereby a single PD pump can replace many centrifugal pumps.”

This is an excerpt from an article published in Engineering & Mining Journal December 2024.