The current business climate in the aggregates industry is characterised by price volatility, shrinking margins and increasing operational costs, among several other challenges that relate to legislative requirements. This is exacerbated by a steady decline in the growth of aggregates demand due to the lack of meaningful construction projects in South Africa.
To survive and mine profitably during such a low growth cycle, quarry owners need to capitalise on the opportunity to improve their productivity and focus on one factor they can control: efficiency. Operational efficiency cannot be achieved by focusing on a single operational process, but by paying attention to the production process as a whole, all the way from blasting and drilling, load and haul, to crushing and screening. Adopting new technologies can also usher in new levels of operational efficiency at quarries.
With that in mind, efficiency is being sought in every sense of the word at SPH Kundalila’s Bridgetown Dolomite Mine. The Cape Town, South African-based quarry mainly produces metallurgical dolomite for Saldanha Steel, as well as agricultural lime and construction aggregates. Several interventions, including a recent plant upgrade and the adoption of three major technologies – a drone system, an innovative dust suppression system and real-time belt weighing scales – are driving new levels of efficiency.
Bridgetown Dolomite Quarry runs two processing plants – the main BDM plant which produces metallurgical dolomite and the Ag Lime plant, which produces -2mm agricultural lime and several selected aggregate sizes for the construction sector.
In 2016, SPH took a decision to upgrade the main BDM plant. A key feature of the plant upgrade was the replacement of the old Svedala screen with the new
As part of the upgrade, the Sandvik H3000 EC cone crusher was also completely refurbished. “We also replaced our V-belt and pulley-driven gearboxes on the plant. We now operate a gearbox and a motor directly without the need for pulleys. A major shortcoming of the V-belt system is that you get slippage on the belts, especially during cold mornings when the belts are wet,” explains Pretorius.
Another key intervention was to change the plant setup. Pretorius explains that previously the plant was an old linear system which ran in a straight line with a ‘scorpion’ belt setup. A scorpion setup comprises two belts running against each other all the time. “We had a lot of complications with the setup, which resulted in breakdowns and downtime,” says Pretorius.
To get rid of the linear setup, the Sandvik H3000 EC cone crusher was rearranged from its usual middle position in the plant, and was moved up the line. “We put in three new belts and a hopper feeder and moved the cone out of the line it was previously located. The hopper was installed to regulate the feed rate of the cone to keep it at choke feed level. Previously, it was fed directly by the screen and you couldn’t choke it. With the hopper feeder, we can regulate the feed to keep it at a constant level,” explains Pretorius.
Pretorius notes that a combination of these changes has resulted in about a 20% increase in production. “We are now able to produce more, mainly because of the hopper feeder, which has created a bit more capacity. Production has also picked up because we have very little downtime,” says Pretorius.
The BDM plant currently produces between 1,000 and 1,500tonnes of material per day. The Ag Lime plant produces about 450tonnes a day of agricultural lime, excluding construction-related aggregates, which are typically produced per order. In terms of overall production, metallurgical dolomite constitutes about 70% of the total offtake per month, while construction aggregates and agricultural lime make up the remaining 30%.
As part of the technological revolution, SPH Kundalila has installed real-time belt weighing scales, which give exact tonnages of material passing selected belts in real time. These have been installed on the metallurgical dolomite product belt, the Ag Lime belt and on the out-loading belt.
A key feature of the belt weighing scales is that they are now GPRS-enabled, which allows them to send information to a server. Management can see, in real time, the exact tonnages passing through each belt, anytime and from anywhere.
“The technology, supplied by Massamatic, an independent manufacturer of industrial weighing equipment based in the Western Cape of South Africa, takes guesswork out of the production equation, which makes it easier in terms of production planning. This is a powerful tool to measure the actual production from crushers and screens, as well as monitoring loadout of trucks,” says Pretorius.
A few years ago, SPH Kundalila also pioneered the use of drone technology for aerial surveying and stockpile management in the South African quarrying sector. The use of drone technology has since been expanded to determine elevations and slope angles in the pit. This is a fantastic tool in terms of pit planning. “We can calculate the amount of tonnages we have already moved out of the pit, and more importantly, the amount of material we can still take out of the pit,” says Pretorius.
“The software gives us concrete evidence to back up our decision-making. We have grown in terms of technology use. The main benefit is that it makes decision-making and planning a lot quicker and efficient,” adds Pretorius.
The drone technology deployed at Bridgetown Dolomite Mine is manufactured by South African-based Aquila Drones, with design and development done by parent company, WCD Engineering Consultants. Aquila Drones was founded in 2014 with the focus to develop specialised unmanned aerial vehicle solutions.
Founder of Aquila Drones, Johan Janse van Rensburg, explains that typically two models are being used for survey purposes. The AQMRS is a multirotor solution used for smaller survey areas in the region of 50hectares. The main advantage is the ability to take off and land virtually anywhere. Operation is also simple. The AQRVS is the fixed-wing platform typically used to survey larger areas up to 500hectares depending on ground resolution required.
Van Rensburg explains that in some cases the perception exists that the land surveyor volumetric calculations are more accurate. “I think it is important for clients to understand that the process used by Aquila Drones still involves a registered surveyor which forms part of the team in setting up ground control markers. The complete survey 3D model is thus absolute geo-referenced accurately to within 2cm,” he says.
The typical resolution targeted during data acquisition is a sub-3cm ground-sampling distance. This roughly equates to a three-dimensional point cloud model accurate to within less than 5cm. This is deemed adequate for volumetric measurements for stockpiles. Accuracies can however be increased to 2cm depending on client requirements.
“Any surveyor would confirm that the accuracy achieved through a precision aerial survey processed with the industry-leading software PIX4D will virtually always yield more accurate volumetric results. This is inherent to the fact that a typical point cloud model would consist of thousands of measurement points on the surface of the stockpile versus only a few typically taken via precision GPS systems,” explains van Rensburg.
Another innovative technology that has come out of Bridgetown Dolomite Mine’s and Van Rensburg’s relationship is a revolutionary and completely new system for dust suppression, the Atomiser. It is a nozzle spraying system that has water and high-pressure air from a compressor.
With its high pressure, it atomises water particles to make a fine mist which captures dust. Bridgetown Dolomite Mine is one of the very first quarry test sites to use the solution in a fixed crushing environment in South Africa.
The quarry is a typical drilling and blasting operation. Drilling and blasting, outsourced to contractor Blasting and Excavating (B&E), is done once a month and blasts are kept fairly large at 60,000 tonnes of material on the ground. Four Bell articulated haulers (2 x B25D and 2 x B25E) are loaded by a Cat 340D excavator in the pit. A Cat 329D is used as a backup excavator, and is in most cases deployed with a hammer to break oversize material.
From the pit, material is hauled to the main BDM plant where it is crushed into spec. Load and haul distances are fairly short and are currently around 1.2km from the pit to the tipping point. Cycle times are, on average, about 8.5 minutes, depending on the point of loading.
A total of five Cat 950 wheeled loaders are used to stockpile and load customer trucks. They are also used to feed two Finlay 683 mobile screens operating on site. The two screens are used to produce road construction material, mainly G products. They are mostly used to supplement production for project-specific contracts.
As part of its compliance with the Proximity Detection System (PDS) legislation, Bridgetown Dolomite Mine is currently one of the test sites for Schauenburg’s surface PDS. It is currently running these systems on its dumpers, front-end loaders and light-duty vehicles, as well as pedestrian units. “Not every machine on site is installed at the moment because we are still a test site,” says Pretorius. “Out of this exercise, we will determine our level of risk, which will inform our level of compliance to the PDS legislation.”
Safety and environmental management are key focus areas at Bridgetown Dolomite Mine. This is demonstrated by high scores in the 2018 Aspasa ISHE and Environmental audits. “We achieved 94.8% in our ISHE audit in 2018 and 97.88% for our Environmental audit, which is showplace,” concludes Pretorius.
