The acid mine drainage (AMD) crisis in South Africa stretches well beyond the country and even the continent. Th ere are thousands of documented, defunct mines in the United States alone – each one a possible environmental AMD hazard, writes LAURA CORNISH.
RITZ Pumps SA, the German/ South Africa joint venture partner for Germany-based fl uid pumps provider ANDRITZ Ritz, has quickly become recognised for its AMD dewatering capabilities, having successfully delivered specialised pumping solutions for various projects initiated to recover (pump to surface) South Africa’s deep-level, mine-induced AMD across the Witwatersrand Basin.
With a solid, growing track record in South Africa, the company is looking to ‘spread its wings’ and implement its heavy-duty AMD dewatering pump technology across the globe. And it will do so in partnership with automation expert Rockwell Automation and piping expert Carl Hamm.
In combination with RITZ Pumps SA’s HDM and ZSM submerged pumps, Rockwell Automation’s Powerfl ex 7000 variable speed drives “guarantee optimal dewatering performance, even in the most toxic environments; while the Carl Hamm ZSM system off ers a safe, quick and fl angeless installation solution. Together we off er an unparalleled AMD dewatering solution,” says RITZ Pumps SA MD Chris Munnick.
“Having worked together so successfully on the installation and operation of two RITZ Pumps SA HDM (heavy duty mining) pumps for the Witwatersrand Central Basin AMD dewatering and retreatment project, we have launched a new platform – AMD Global – which entails providing similar solutions on a global scale to resolve AMD threats,” Munnick continues. Although the Global AMD initiative was only established by RITZ Pumps SA late in 2015, the three companies have been focusing intensively on the concept and are already looking for enquiries.
The AMD pump of choice
RITZ Pumps SA’s HDM duplex stainless steel, double suction motor, zero thrust pumps outweigh the use of single-suction submersible motor pumps for pumping huge quantities or from great depth, which is generally associated with extreme loads on the unit and often leads to overloading and untimely shutdown.
RITZ Pumps’ double-suction motor delivers greater durability which provides full compensation for axial thrust, thereby placing less strain on the pump and ultimately resulting in a longer pump lifespan. The HDM pump series in particular includes two contra-rotating submersible motor pumps arranged on top of each other and driven by a continuous pump shaft. The suction branches of the two pumps are located at the ends of the HDM module.
Each pump transports half the capacity to the middle of the pump at full pressure. There, a deviating stage directs the fl ow to the pressure line via the external casing channels. Loads on the unit are kept to a minimum and the thrust bearing is no longer subjected to tons of thrust. This signifi cantly reduces wear and tear, increasing service life to up to 20 years or more.
The division of work between the two hydraulics not only achieves complete compensation for the axial thrust, it also halves the suction velocity outside the pump. This protects the well walls around the intake openings and minimises the intake of abrasive solids and silt.
With half the delivery fl ow going to each pump, smaller impeller intake cross sections are possible and therefore lower circumferential velocity in the seal gaps.
Every pump featuring HDM is tailormade from standard modules to meet specifi c application requirements. Each HDM for example features a heavy duty motor specially adapted to power usage of up to 14 000 V. This minimises both the cross sections for energy transmission and transmission losses.
RITZ pumps can be suspended from surface level using the Carl Hamm ZSM duplex stainless steel, high pressure, high tensile, quick coupling system and operate from within a 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.
Rockwell Automation drives critical
“It is Rockwell Automation’s PowerFlex 7000 variable speed drives (and Carl Hamm piping) that enables our equipment to draw down at depth. Finding a suitable variable speed drive (VSD) supplier is not an easy task, Munnick notes, “as the majority of suppliers’ products require secondary fi ltering equipment to develop suitable sinusoidal waves required for electric RITZ MC-T (modular cooling technology) medium voltage (MV) motors. “Depth is extremely important as many AMD applications require cable lengths up to 1 500 m. Because Rockwell Automation’s VSDs don’t require additional secondary fi ltering equipment, they are well-suited to applications with even longer cable lengths.”
“None of the ‘competitor’ suppliers,” adds Henry Craukamp, sales manager at Rockwell Automation – Medium Voltage, South Africa and sub-Saharan Africa, “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 15 km from source, so 1 500 m 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. “Together with the RITZ pumps, our VSDs offer a 99.9% availability to deliver the maximum capacity and guarantees full flow at all times, i.e. pumping water at approximately 1 500 m3/hour, or 410 ℓ/ second per pump.
Aside from its long functional motor cable length, the Rockwell Automation PowerFlex 7000 also prevents common mode voltage. The symmetrical gate commutated thyristor (SGCT) power components have a non-rupture, non-arc failure mode, meaning a fault is contained within the device helping to reduce the risk of an incident under failure conditions. This enables Rockwell Automation to off er the lowest mean time to repair (MTTR) but also helps off er improved personnel safety.
All systems can be run and maintained from the surface so there are no secondary infrastructure costs associated with the application. Rockwell Automation also off ers 100 000 hours mean time between failures (MTBF) compared to its competitors. MRA