Problems with valves can lead to unplanned downtime and equivalent losses in output. This is why saving on this specific product can end up being expensive. With the help of Metso’s service experts, Gold Fields Ghana’s Tarkwa gold mine has been able to achieve consistent reliability, leading to improvements in the plant’s overall efficiency.
This article first appeared in Mining Review Africa Issue 5 2018
Quality issues leading to unplanned downtime
Valves play an important role in the CIL (carbon in leach) refining process, which Tarkwa mine adopted in 2004, both in terms of their numbers and functionality.
Premature failure has the two-fold outcome of unplanned downtime and subsequent losses in output.
Metso’s service sales engineer for valves business, Christian Appiah, explains that valves in the mining environment work under extremely demanding conditions. “Valve and actuator failure can arise for a number of reasons. For example, high levels of pollution owing to dust and other contaminants results in very poor air quality. Added to this are the problems of very high ambient temperatures and pressures, not to mention the challenges posed by vibration.
An erratic and low-voltage power supply also compounds potential issues,” he says.
Appiah goes on to explain that the valves fitted as original equipment to the second generation plant performed as expected in terms of life expectancy; however it was after routine replacements that problems began to emerge.
“There seemed to be a problem with quality, even in instances where the valves were replaced by seemingly identical products from the same brand. This is something that could be attributed to the use of lower grade materials. One of the challenges in this situation is that supply chains regard valves and similar products as commodities. Price therefore, becomes the main motivating factor behind the buying decision, irrespective of potential consequences down the line.”
Metso has enjoyed a longstanding relationship with Gold Fields Ghana through its supply of heavy duty equipment, including crushers, pumps and mills. It was from this association that Tarkwa was approached with regard to the possibility of sourcing alternative valve requirements from Metso’s valves business services.
Step changes in efficiency and reliability
That was the beginning of an intensive process involving a great deal of groundwork and technical analysis over a five-year period.
Appiah was deeply involved in the process that ultimately provided the solution to the customer’s needs.
To cover the demanding application requirements, the best fitting valves were selected from Metso’s large portfolio of products for different mining and minerals processing plants. For the Tarkwa mine, the solution was control and on/off valves, including ball, butterfly and V-port control valves that had been supplied in 2015 as replacements for items that solutions BOXBOX had reached the end of their working lives.
“This was very much a team effort between technology and sales, and this level of cooperation was essential as CIL is a massive process in a plant of this magnitude. A key component in the planning phase prior to the adoption of Metso products for the CIL process was Nelprof, an advanced software solution that helped us to select the best fitting control and on/off valves for the specific application,” says Appiah.
The dual advantages of the scientific selection and installation of valves to the correct specification and of a durable quality were soon recognised by Tarkwa Engineering management. “There has been significant reduction in downtime and gain in productivity matched by reduced operational expenses,” notes Solomon Boateng, plant engineer for Tarkwa mine – CIL.
The Tarkwa mine engineering management has been satisfied with the performance of the installed Metso valves as they have yielded step changes in their consistent reliability and the plant’s overall efficiency.
Boateng puts the positive transition from unreliability to constant productivity into context: “These valves have now given us peace of mind concerning the operation of the critical elution circuit in the CIL process. The use has been extended to other essential segments of our recovery processes.”