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Effective acid mine drainage in Central Basin

The start of implementing the TCTA’s long-term solution to reduce Acid Mine Drainage in Gauteng’s Central Basin. The start of implementing the TCTA’s long-term solution to reduce Acid Mine Drainage in Gauteng’s Central Basin.

Teaming with RITZ Pumps SA has enabled Rockwell Automation to lend its knowledge, experience, expertise and products in helping to solve one of South Africa’s high-profile national problems – acid mine drainage (AMD), before it negatively affects natural water resources.

The project, taking place at Gauteng’s Central Basin, is the first phase of the long-term solution to reduce AMD in the Basin before environmental critical levels (ECL) are reached and to retain the level below ECL into the future. The project is being implemented by TCTA (Trans-Caledon Tunnel Authority) on behalf of the Department of Water and Sanitation.

Rising water levels and flooded underground pump stations have negated any possibility of using conventional pumping solutions, thus requiring a specialised submerged pumping solution. Enter RITZ Pumps SA, a German/South Africa joint venture resulting in a South African black-owned partner of the multi-national ANDRITZ Ritz, Germany. Two of RITZ Pumps SA HDM (Heavy Duty Mining) Duplex Stainless Steel, Double Suction, Zero Thrust Pumps were purchased by Central Rand Gold (CRG) as part of their contribution to solving the AMD problem and were donated to the government to ensure the successful implementation of the Central Basin AMD project. These pumps are suspended from surface level by the Carl Hamm ZSM Duplex Stainless Steel, High Pressure, High Tensile, Quick coupling system and operate from within the mine shaft. This eliminates the need for maintenance teams to enter the mine and the necessity for secondary infrastructure such as man hoists, ventilation and conventional mining equipment.

Deeper depth through Rockwell Automation

“Although the equipment was procured by CRG for a deeper abstraction than the current water level, it is our PowerFlex 7000 variable speed drives and Carl Hamm piping that will enable the original equipment to draw down the basin from the current depth to the designed depth,” points out RITZ Pumps SA MD Chris Munnick. He says that one of the challenges was the difficulty encountered in finding appropriate variable speed drive (VSD) suppliers, as the majority of suppliers’ products require secondary filtering equipment to develop suitable sinusoidal waves required for electric RITZ MC-T (Modular Cooling Technology) Medium Voltage (MV) motors. “The depth for the application is extremely important as many of our applications require cable lengths up to 1,500m. Rockwell Automation solved this problem for us without additional secondary filtering equipment requirements as their VSDs are well-suited to applications with even longer cable lengths.”

“None of the ‘competitor’ suppliers,” adds Henry Craukamp, Sales Manager – Medium Voltage, South Africa and Sub-Saharan Africa, Rockwell Automation, “are capable of reaching the cable lengths we do without additional custom-designed motor filtering systems. We have done successful tests with cable lengths up to 15km from source, so 1,500m poses no real challenge. This is achieved through a virtually perfect current and voltage output waveform which also has the added benefit for our customers to use standard motors and motor cables.”

“Further contributing factors to the synergy in our collaboration are our local engineering and service personnel, the VSD performance with the electrical system and the motor, and the reliability, ease of use and maintenance,” Craukamp adds. “The plant will not be shut down nor switched off, which requires the pumps and VSDs to have 99.9% availability to ensure they can deliver the maximum capacity to guarantee full flow at all times, i.e. pumping water at approximately 1,500m³ per hour, or 410L per second per pump.

Relationship cemented

“Cementing our relationship for this project,” adds Nevin Turner, industry account manager, “is the use of the Rockwell Automation PowerFlex 7000 which, aside from its extraordinary long functional motor cable length (approximately 1,500m from the above ground VSD to the below ground pump), helps to ensure that we don’t experience the problem of common mode voltage. The Symmetrical Gate Commutated Thyristor (SGCT) power components used has a non-rupture, non-arc failure mode, meaning the fault is contained within the device helping to reduce the risk of an incident under failure conditions.” This enables Rockwell Automation to offer the lowest mean time to repair (MTTR) but also helps offer improved personnel safety.”

All systems are run and maintained from the surface so there are no secondary infrastructure costs associated with the application. This, and the fact that Rockwell Automation offers 100,000 hours mean time between failures (MTBF) compared to its competitors which is significantly lower, leaves no doubt that Rockwell Automation is The company of choice for this specific project.

RITZ Pumps SA was able to offer a turnkey solution through its alliance with Rockwell Automation, Carl Hamm and Woodrow Engineering, a well-reputed Rockwell Automation Recognised Systems Integrator for all monitoring and control.

Rockwell Automation was recently awarded the contract for the Eastern Basin AMD solution – the third leg of the AMD project, which will entail solutions identical to that of the Central Basin. This contract makes Rockwell Automation the single process control provider for the TCTA’s AMD project in South Africa.

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