Modikwa is located in South Africa‘s Limpopo Province, situated less than 120km from the world famous Kruger National Park. The region is rich in platinum reserves. Modikwa is a joint venture between African Rainbow Minerals and Anglo Platinum and forms part of the Bushveld Igneous Complex, spanning an area of 14,278ha. The Mine has been in operation since 2003 and plays a crucial socio-economic role with South Africa being the world’s largest producer of platinum. It has 5,000 employees in total and contributes significant wealth to the country’s gross domestic product (GDP).
The mine is made up of two shafts, North and South; and is a 240,000t per month platinum production facility. Employing a hybrid mining technique where mechanised methods are used for the main developments and the narrow, 60cm reef is conventionally stoped using a down-dip method. While excavation of the ore is done by conventional means, the mine employs trackless mining vehicles, which entails the use of tyre-driven or mobile machinery underground as opposed to using tracks as was prevalent in the past. This offers greater flexibility of the fleet as it is not constrained to one area or one level of the mine and machinery can move to and from production points much faster.
Machines with mtu Series 900 engines
With its 6m long boom reaching to the face, drill rigs pierce the solid earth, punching holes approximately 5cm wide; just enough to house and make way for the explosives. If the drill rig goes down, production slows. And in an operation that loses on average R10 million for each day that production stops, reliability and peak performance are non-negotiables. It is one of the only machines at Modikwa that stays underground, even as blasting takes place.
The three drill rigs on North and South shaft stay underground for a full week, being re-fuelled underground from containers delivered to it, when required. One drill rig is driven by a mtu type 4R 904 engine. Looking at the distances this machine has to drive underground — a oneway distance from decline to the face of up to 4.5km — the most impressive feature is the power the engine delivers: rated power of 129kW at 2,200rpm. Rudi Coetzee, engineering foreman at Modikwa and responsible for all machinery on the North shaft, confirms this, “The mtu Series 900s are relatively new engines, especially in the South African market. They have been operating in Sandvik vehicles at Modikwa for two and ahalf years. In this time, they have outperformed others in their class.” Sandvik South Africa has a performance service contract with Anglo Platinum to service the machinery. This includes dump trucks and load haul dumpers (LHD) as well as drill rigs and roof bolters deployed underground, in the development of the mine
Once the drill rig has finished its work, the face is charged up with explosives, and then blasted. After blasting, the LHD loads ore which is put into a dump truck and moved from the face to the conveyer belt. The conveyer belt takes the ore out to the plant. One of the dump truck applications is powered by a mtu type 6R 926 C72 engine with rated power of 240kW at 2,200rpm. Being one of the smaller dump trucks on the mine, it more than makes up for its size in workload. For this reason it is crucial that it remains working; for maximum periods, at maximum output. This is certainly evident at Modikwa, as Coetzee explains, “The mtu type 926 engine is performing at an excellent rate of approximately 210 to 240 hours of running time per month. The standard time is usually between 110 and 180 hours, which is also good. Certainly a great endorsement at an operation that, on average, generates up to R1 million an hour on these units.
Conditions above ground and underground for the engines
With high temperatures and a healthy annual rainfall, the lush, subtropical conditions on the surface mask the harshness of the underground environment. In this part of Limpopo the temperature in summer is up to 42°C while in winter it plummets to an average of -2°C. During the rainy season, the area is known to receive in excess of 200mm of rain in a 24 hour period. Furthermore, 21 mines in operation in the area and another 16 planned for development, attests to the fact that it is one of the highest concentrations of lightning strikes in South Africa. Everything that happens underground is intense. Heavy machines manoeuvre through tight spaces. It is abrasive and combative. The sound is deafening, temperatures reach in to the mid 40s°C — sustained by the heat that the hard-working engines produce. Dust plays its part in challenging engine performance and in the newly developed areas it is flooding that is the major issue. Water manifests from underground due to seepage and a high water table.
Additionally, the drilling process produces water. It is not uncommon for an mtu service technician to be working knee deep in water, while servicing a vehicle underground. “It is important that the mtu Series 900 engines operate no matter what conditions are experienced underground,” explains Coetzee. “The biggest challenge is the vast temperature range and the potential problems related to this.” Because the mine forms a closed loop system, cold ventilated air has to be physically pushed through the mine from the surface. Furthermore, burning as little fuel as possible and the after effect of releasing carbon monoxide, which needs to be pushed out of the mine by a fan is fundamental. “These challenges are considered when selecting machinery and equipment to work underground,” says the engineering foreman.
Fuel consumption — low and efficient
Automated features on the mtu Series 900 engines are what excite Coetzee the most, that is, the ability to have the engines think for themselves underground. Asked what features they thought most significant in fuel efficiency, Coetzee quickly states, “As the engines have the capability of decelerating themselves, this automatically results in improved fuel consumption. Additionally, if the correct amount of oil is not put into the engine, it just will not start.” Coetzee sees the great benefit in the automated idling component. The engine can be set for a ten minute period of idling, for example, while waiting for the ore to generate. It depowers itself, cutting down the engine, using less diesel and pushing out less exhaust gas. “The less gas and heat they emit, the cooler the mine underground. Moreover, the low consumption rate keeps the cost per ton of material moved low at Modikwa, and that is crucial,” says Coetzee.
mtu automation system
The engine control module (ECM) on both mtu type 904 and 926 engines enables the precise interaction between key engine systems. With the ability to extract and analyse crucial information, gathered from the engine over an extended period, engine lifecycle, engine performance, mine operating efficiency and a host of other areas are dramatically improved. The system prevents further deterioration that could result in major costs and quicker loss of the engine. It also improves planning, making sure that it does not impact the mining or production staff while making it easy to determine the service needed, resulting in a decrease of downtime for the operation at Modikwa. Long-term stability of the engine functions to ensure that mtu engines remain as economical, clean and powerful over their entire service lives as they are when new. This enables the system to compare the readings obtained from the sensors with the target settings for optimum engine performance.
This ensures that the engine is stable in terms of fuel consumption, emissions and performance over the entire lifespan, since the engine management system ensures that compensation is made for any changes resulting from wear and tear and environmental conditions. Thomas Phiri, Sandvik Contracts Manager, sees the benefits from a service point of view, “The ECM assists with forecasting. We can predict when the engine is going to need maintenance, as well as indicating the services required, components to change, as well as new components needed in order to extend the life of the engine. From the history of operation on the machine my team sit down and plan what work needs to be done on the engine.” There is also a powerful protective element that ensures the engine is not mistreated. The protection is provided in the form of sensors which indicate coolant temperature and engine temperature. If the temperature increases in an irregular manner, the ECM will raise an alarm, and if ignored the engine will de-rate to limp mode (reduced power), saving it from getting destroyed or harmed.
Es ist auch eine leistungsfähige Schutzfunktion vorhanden, die sicherstellt, dass der Motor nicht zu stark belastet wird. „Der Schutz wird in Form von Sensoren realisiert, welche die Kühlmitteltemperatur und die Motortemperatur melden. Steigt die Temperatur in ungewöhnlicher Form an, erzeugt das ECM eine Störmeldung, und wenn diese ignoriert wird, reduziert der Motor seine Leistung und schützt sich so vor Zerstörung oder Beschädigung.
After sales service
mtu works on a service exchange basis, estimating a down time of between eight and 24 hours for replacing an engine. If not planned correctly, the machine can stand for up to two weeks waiting for parts, at great costs. This is one of the reasons Coetzee is passionate about service and the impact good after sales service has on making his job easier. “The single most important criteria for selecting an engine or a machine group is after sales service. We must know from the company that we are dealing with that they are willing and able to help us 24/7, because we run all the time. We don’t stop for Christmas or New Year’s, it’s a 365 day production line. mtu was one of the few companies that could stand behind us and make people available for those times.”
Currently mtu is permanently on-site, with one representative per shaft, every day, Monday to Friday. This involves checking and maintaining the machines, downloading information and providing parts. Moreover, the mtu representatives are also on 24 hour stand-by. Phiri can therefore focus more time on other parts of his job, asserting that, “Because the mtu service technician is on-site to give us advice on the engine before major problems arise, it gives us an advantage. Having an arrangement with mtu assists Sandvik in minimising engine downtime and the cost of the machine. Furthermore, mtu transfers skills and knowledge to Sandvik service technicians and mine vehicle operators and artisans. From Sandvik’s perspective, this helps in keeping our client happy.”
When an engine goes down while underground at Modikwa, mtu is called and the problem must be rectified within a specified period. “Our target is always two hours in which that machine must be up and running,” says Phiri. Previously mtu technicians were called out from Johannesburg, 360km away. A localised mtu service point was set up in the little town of Burgersfort, 20km from the mine, improving their service and strengthening their commitment to Sandvik.