10 THE SOUTH AFRICAN MECHANICAL ENGINEER VOL 64 March 2014

COVER STORY

The planned installation in March 2014 of 2 x Ritz HDM 6737.3/15 stage double suction heavy duty mine dewatering pumps with 2400 Kw 6600 Volt 50 Hz submers-ible motors, originally procured by Central Rand Gold (CRG), will now be installed into South West Vertical Shaft in Germiston by TCTA to pump ± 1 500 M3h per unit to the treatment plant. The shaft is made avail-able by Durban Rhoodepoort Deep (DRD).

The fact that the pump station is so far underground, yet still needs to maintained, means that a dead mine has to have a supply of fresh cooled air for people to service and operate the pumps. In fact, such a dead mine has to be operative just like any active mine in terms of power supply for hoists, ventilation, cooling and lighting, costing million in annual operating costs.

Special pumpsThis need not be the case. “Our core busi-ness is mine dewatering regardless of water quality, ie, Potable water or Acid Mine Water (AMD). It is also applicable whether it is an active or a dead mine. Our pump ap-plication was developed specifically for this purpose and has for many years been used in mining everywhere else in the world,” Chris Munnik Ritz Pumps MD tells “SA Mechanical Engineer.”

Above ground pumping“The beauty of our system is that our pump is assembled above ground and then “hung free” suspended from surface so you don’t need underground access to get to the pump station as is generally the case in South Africa. The pump is simply suspended in the shaft opening where it can hang free to 1000 metres with piping from 80nb to 600nb and achieve heads of 1500 metres. Or we can even drill a borehole from the surface straight down into the water source, suspend and hang the pump into the water and pump out directly without having to go through the shaft with a complex piping sys-

Dewatering Mines

Seth Phalatse, Chairman

Chris Munnick, managing director

tem as is required for a traditional underground high pressure pump sta-tion setup.”

The system is not only for old mines. New mines in Australia and up in Africa are now installing this system from the outset. “Although it is sometimes chal-lenging to retrofit our system, it is very cost-effective to install it on new mines where the conventional mine dewatering system of building and un-derground pump station today liter-ally cost millions more. One of the greatest advan-tages is that if we know where the water is, we simply

go straight down to it through a borehole and do not need a shaft to get the water out,” Chris adds.

TechnologyThe use of single-suction submersible motor pumps for pumping huge quantities or from great depths is associated with extreme loads on the unit in the design of the HDM (heavy duty mining) pump system that comes in a wide range of sizes. The higher the pump performance, the stronger the axial thrust exerted on the pump, the motor and its thrust bearing. The consequence is overloading and untimely shutdown. The solution is to double up, meaning greater durability. Chris explains,

The beauty of our system is that our pump is assembled above ground and then “free hung” suspended from surface so you don’t need underground access to get to the pump station

Although some mines are inoperative (‘dead’) mines, they still need to be dewatered to avoid contamination of underground water and to keep the water at an acceptable and safe level. Or to bring this contaminated water to surface

for treatment, ie, AMD (Acid Mine Dewatering).

THE SOUTH AFRICAN MECHANICAL ENGINEER VOL 64 March 2014 11

ON THE LIGHT SIDECOVER STORY

“This is what our design is all about. A double suction pump that provides full compensation for axial thrust. In short, the HDM is designed for a longer life.”

How it worksWith the HDM system, two contra-rotating submersible motor pumps are arranged on top of each other and driven by a continuous pump shaft while the suction branches of the two pumps are located at the end of the HDM module. Each of the two pumps transport half the capacity to the middle of the pump at full pressure.

There, a deviating stage directs the flow to the pressure line via the external cas-ing channels. The double suction design completely compensates for the axial thrust while loads on the unit are kept to a minimum and the thrust bearing is no longer subjected to tonnes of thrust. “This significantly reduces wear and tear resulting in the extended service life we are achieving.”

Furthermore the division of work be-tween the two pumps not only achieves complete compensation for axial thrust but the impeller tip speeds are reduced resulting in less wear and halving the suction velocity outside the pump. This protects the well walls around the intake openings and minimises the intake of abrasive solids and silt, a compelling benefit. With half the delivery flow going to each pump, smaller impeller intake cross-sections are possible and therefore lower circumferential velocity in the seal gaps.

Every HDM pump is a once-off as each one is tailor made from standard modules for each specific application. There is the hydraulics module that utilises the optimum combination of impeller diffuser and casing, leading to the best possible adaptation to a desired operating point at extremely high efficiency. Then, the materials module provides a wide choice of materials enabling flexile adaptation to suit all combinations of chemical or abrasive operating conditions.

The motorFinally, even the motor is modular. Each HDM features a heavy duty mo-tor specially adapted to power usages

of up to 14 000 volts and sizes up to 6 500kW. “As unbelievable as it may sound, our electric motor design is unique in that it is filled with water for cooling. Like many great innovations, the principle behind our MC-T (modular cooling technology) is amazingly simple. Its all about motion,” Chris adds.

On the lower shaft end of the ro-tor, there is a suction and pressure optimised pump impeller. One of its two main tasks is to cool and lubricate the nearby axial bearing, but it also ensures a constant flow of cooling liquid in the right direc-tion. “The liquid moves upwards through the inside of the motor, and the cooling channels developed in house by us, define the precise route via all thermal sources to evacuate the liquid effectively.”

When it arrives at the top, the heat in the liquid is transmitted to the outer wall of the motor and the heat escapes through the surface to the medium being pumped. And then the whole procedure starts again. For really high temperature condi-tions the cooling performance can be enhanced through the use of additional heat exchanger modules fitted onto the unit.

BEEThis technology is not new and is being used worldwide but has not yet been explored fully by the South African mining industry. It thus requires us to be more aggres-sive in our marketing efforts in this industry. We support the develop-ment of previously-disadvantaged South Africans hence our level one black-owned BEE status.

Our company has been contracted to install various pumps in a number of countries in Africa but fact of the matter is anybody who is serious about dewatering must come and talk to us. We have purpose-designed systems to solve any dewatering problems cost-effectively.

Ritz Pumps, Chris MunnickTel: (011) 397-5616,

As unbelievable as it may sound, our electric motor design is unique in that it is filled with water for cooling