EXXARO’S BELFAST MINE GETS CONCOR EXPERTISE

Concor Infrastructure is building dams, roads, platforms and other works at Exxaro’s new digital coal mine near Belfast in Mpumalanga province.

At work since October 2017, Concor Infrastructure is constructing four major dams, 26 concrete platforms and terraces, 37 internal roads of 16 km in length, and the upgrade of almost 13 km of provincial roads, among other aspects of the mine.

According to Concor Infrastructure contracts manager Pierre van Vuuren, dams are being lined with both a geosynthetic clay liner (GCL) and high density polyethylene (HDP) sheets, in compliance with the water use licence and related environmental regulations. Various structures around the dams are also being installed, including large silt traps, drying beds, inflow chutes to prevent scouring, and spillways and sumps.

Among the concrete platforms and terraces are two primary crusher bases being built for the run-of-mine crushing facilities. The various structures being built by Concor Infrastructure on the mine will demand almost 350 tonnes of steel reinforcing, and nearly 2,700 tonnes of bulk cement. Other inputs will be around 15,000 tonnes of 19 mm aggregate and nearly 13,000 tonnes of crusher sand.

Dams are lined in compliance with environmental regulations and best practice.

Extensive upgrading is being done on the D1770 and D1110 provincial roads – for the transport of coal to the rail siding – including eight major culverts under the roadway. For all the project’s road works, almost 9,5 km of subsoil drains is to be installed, as well as 2,7 km of stormwater culverts. G5 and G6 construction material comes from an external quarry and crushing plant located about 30 km from site towards Carolina.

Contracts manager Mabandla Dlamini highlights the substantial local impact of the project, including the accommodation of a core labour complement of about 180 personnel in the Emakhazeni municipal district. The overall workforce managed by Concor Infrastructure, with contractors, totals closer to 700 – who are all transported 30 km daily by the local taxi network.

Dlamini also points out that various subcontracts are outsourced to local small enterprises, such as drainage, stone pitching, paving, kerbing, fencing, security services and catering. Diesel is also sourced from a local fuel depot in Belfast; the project is expected to consume about 4,3 million litres of diesel in site-wide applications.

Over 150 items of plant and equipment are active on the site, says site agent Sarel van der Berg, with about 40 items such as articulated dump trucks, tippers and graders from local plant hirers.

AFRISAM CONTINUES TO FOCUS ON CARBON EMISSION REDUCTION

It is not business as usual for AfriSam, who has been working hard towards reducing its impact on the environment for many years. Since 1990, this leading supplier of construction materials has reduced its C02 emissions by 35%. But this, according to Hannes Meyer, cementitious executive at AfriSam, is not where it ends.

Speaking at a presentation to media at its Dudfield cement plant near Lichtenburg in the North-West province, Meyer said AfriSam continues to cut the carbon footprint of its cement. Efforts focus on using less energy in the production of clinker, while making more use of extenders like fly-ash and slag.

“We are probably South Africa’s leading company in our understanding and application of extenders in cement,” he said. He emphasised that this field holds great scope for creating more environmentally friendly cements, but required considerable technical expertise. With its many years of experience, AfriSam was applying that expertise in its ongoing cement innovation.

Limestone mining at Dudfield began in 1949, with the first kiln established in 1965. Today, the plant produces over a million tons of clinker on its Kiln 3 plant to meet market demands. The plant has a cement production capacity of over 1.3 million tons. The plant also has the flexibility to supply bulk cement by both road and rail, as well as its own bagged cement. There are 65 years of proven limestone reserves on AfriSam Dudfield’s 3,608 ha mining licence.

AfriSam invests constantly in energy saving strategies at its cement plants. Since 1990, it has achieved a cumulative reduction of 31% of cement-specific thermal consumption, measured in megajoules per tonne of cement.

Meyer highlighted the potential of the new carbon tax – in force from 1 June 2019 – to incentivise energy-saving innovation.

“The depressed state of the economy has dampened many of industry’s good ideas, and if carbon tax revenues could cover industry incentives, the resulting innovations would have a range of positive spin-offs. Apart from easing demand on Eskom’s grid, this would also contribute toward the country’s Paris Agreement obligations,” Meyer said.

AfriSam’s commitment was clear to see, he said, being the country’s first cement manufacturer to equip all its kilns with bag filters. This brought emissions to below even the European standard of 30 mg/m3.

USING QUALITY MOTORS AND GEARBOXES OPTIMISES SCREEN ECONOMY

Harsh operating conditions on vibrating screens demand high quality engineering and the strictest tolerances for unbalanced motors and gearboxes, or they simply do not last.

According to Kenny Mayhew-Ridgers, chief operating officer at Kwatani, local design and manufacture to the highest standard is therefore a non-negotiable. The company designs its own range of motors and locally manufactures the gearboxes for its vibrating screens.

“We design our own motors with local conditions in mind, giving the customer a high performance and long lasting product,” says Mayhew-Ridgers.

This includes optimal sealing arrangements for keeping electrical components dry and clean. Power cables, for instance, must always enter from the underside to prevent water ingress. The design must consider various orientations of the motor, depending on the angle of installation. Dusty conditions on mines also present a challenge.

“Dust ingress can compromise the sealing configuration of the lid,” he says. “Our design is therefore like a top-hat, so the O-ring is not on a flat surface but rather on a cylindrical, vertical surface. There is even a double-sealing arrangement for the lid, which includes a gasket.”

Kwatani’s gearboxes are fully locally manufactured, with only the high quality bearings imported direct from leading global producers. Gearboxes comprise two shafts, each with its own set of unbalanced weights linked to each other by a gear to achieve synchronised motion. Gears and shafts are locally fabricated by selected suppliers, while the housing is cast by a local foundry and machined to exacting specifications.

“We have spent a great deal of effort on the sealing configuration, to ensure no oil leaks,” he says.

He notes that Kwatani is probably the only OEM that services its own gearboxes. This ensures adherence to strict tolerances, so that units have sustained performance and longevity.

He also highlights the massive centripetal forces that are exerted on the screening machine by the unbalanced motor and gearbox. This make it vital to secure them well to the screen.

“To achieve this, we specify our own fabricated bolts, nuts and washers,” he says. “If sub-standard fasteners are used, components can come loose and cause extensive damage.”

Unbalanced motors usually have to be installed at an angle. Taking account of the weight of these components, there are rigging points all around the housing to manipulate the angle of installation. The feet are normally larger than those of competitors, for a better contact surface.

“If there is the slightest imperfection in the flat surface of the join, this can cause costly damage to the drive and the screen,” says Mayhew-Ridgers. “This is why OEMs like Kwatani have such detailed installation procedures on issues like torqueing of bolts. Installers and maintenance teams need to stick closely to these specifications.”

UNDERSTANDING DESIGN CHOICES FOR VIBRATING SCREENS

Don’t generalise about the advantages and disadvantages of different vibrating screen technologies, advises Kwatani CEO Kim Schoepflin; the key consideration is the application.

“When a customer considers their options for a screening machine, there are a number of good technologies from which to choose,” Schoepflin says. “The appropriate technology choice will depend on the application, and we believe there is a space for every technology.”

Brute force screening is the most common technology employed among mining screens. Its benefits include being generally cost effective, relatively simple to maintain and economic in terms of life cycle costs, all of which translate into lower Total Cost of Ownership (TCO).

“Having the mechanical and metallurgical knowledge in-house, Kwatani can provide the technology that best suits the application,” she says. “We are not tied to one technology, and our primary focus is on understanding exactly what the customer needs, and providing a solution that is engineered for tonnage.”

Twin-mass or resonant screens, which run very close to a natural frequency, have a self-amplification benefit, says Kenny Mayhew-Ridgers, Kwatani’s chief operating officer.

“This gives the screen a greater energy-efficiency,” he says. “There are, however, limits on the size of these units. In addition, maintenance is more costly as springs or rubbers must be changed regularly or the efficiency benefit is lost.”

He notes that twin-mass screens also tend to be heavier. This can cause confusion when presenting technology comparisons to customers.

“Often the overall mass of the twin-mass screen is compared with the mass of the brute force screen, and this is obviously not correct,” he says. “Rather, it is the deck sizes that must be compared, as this is the element that does the work.”

While the mechanics that drive the screening process is different, the motion of the panel is what is important. This is where interaction occurs between the particles and the screen panels. The efficiency of the process then depends on the screen’s speed, frequency, drive angle and movement of the panel relative to the particles.

While some proponents will generalise about common challenges with brute force screens, Mayhew-Ridgers notes that these observations are seldom valid. Various manufacturers offer a range of brute force technology solutions, each with its own benefits.

Schoepflin highlights that Kwatani works to raise awareness in the industry about what each technology is about. This makes it easier for users to make informed decisions about the technologies they choose. She also says it is important for users to be confident that their chosen screen is well supported by local experts.

“It is vital for OEMs to prioritise the customer’s application when considering the basic screen technology and design,” she concludes. “While optimising screen panels to achieve higher screening efficiency is always an option, it is not the silver bullet.”

INCREASED CALL FOR SLURRYSUCKER TO DESILT

Increasing pressure to lower the total cost of ownership (TCO) has seen many mining operations review their water management strategies. Integrated Pump Rental reports that this has led to increased enquiries about its locally manufactured solutions that mitigate the challenges of silted process water ponds.

Ruaan Venter, development manager at Integrated Pump Rental, says there is now a more proactive stance being taken on the monitoring of these water reservoirs.

He says this is most encouraging as Integrated Pump Rental has been calling for a more systematic approach to the monitoring of process ponds. “Apart from the fact that South Africa is a water scarce country, we have always maintained that the proactive monitoring and regular desilting of process water ponds will save customers in the long run.”

Adding to that challenge of water shortages is the need for mining operations to reduce their reliance on municipal water supplies. This means that efficient monitoring of process water ponds is critical in terms of recycling and reuse of water for the plant and other purposes on a mine.

Ongoing monitoring of process water ponds will facilitate desilting activities on a rotational basis. This will eliminate the disruption of unexpectedly having a pond out of service.

Venter adds that the economic value of the minerals in the silt should also not be forgotten and this material can be pumped back into the plant for reprocessing. The value claimed from retreating the silt can, in many instances, pay for the pond cleaning activity.

“Taking this concept one step further, we have found that mines are investing in their own SlurrySucker equipment,” Venter says.

The SlurrySucker is was developed by Integrated Pump Rental for applications where the water retention and water holding capacity of process ponds in threatened. It is also ideal for the dredging and cleaning of water capture areas where silt or slimes has become an issue.

This innovative dredge unit needs only a 400 draught of water above the sediment for the floating unit to operate. A dewatering pump takes the top layer of water and feeds it down to the dredge-head, where the slurry is agitated so it can be pumped out.

“Our SlurrySucker is available for outright purchase which is a popular option currently, but we also offer the unit on a rental or project agreement where our team will conduct the work for the end-user,” Venter concludes.

TURBINE DRIVE TRAIN OVERHAULED IN JUST SIX WEEKS

In a recent major overhaul of a 70 MVA turbine generator set, Marthinusen & Coutts, a division of ACTOM (Pty) Ltd, contracted with South 32’s Metalloys to take full responsibility for entire drive train refurbishment.

Working in collaboration with business unit ACTOM Turbo Machines, Marthinusen & Coutts completed the work successfully within six weeks. The electrical generation plant is at Metalloys’ manganese plant in Meyerton, Gauteng.

According to Mike Chamberlain, Marthinusen & Coutts’ marketing executive, this achievement showcased the capacity of the divisions to take full control of large mechanical and electrical refurbishments. Chamberlain highlights that the customer did not want to split the responsibility for the complete generator and turbine drive train between separate contractors.

“Marthinusen & Coutts and ACTOM Turbo Machines’ capabilities enable us to control the entire process, offering peace of mind to customers, coupled with optimised cost efficiencies,” says Chamberlain. “This also reduces customers’ risk and managerial effort in dealing with multiple suppliers.”

The scope included a complete inspection of the turbine rotor and internal components, as well as runout and dimensional inspection on the rotor. Inspections incorporated glass bead blasting and non-destructive testing of many components.

High-speed balancing of the 13 tonne rotor was conducted, and turbine rotor journals were repaired. White metal bearings were relined, and the thrust bearing was modified to improve fitment in the bearing casing. Positive material identification tests were conducted on all the studs, nuts and shaft seals. A complete 3D scan was done of the centreline to allow reverse engineering drawings.

At is repair facility in Cleveland, Johannesburg, Marthinusen & Coutts also performed a number of inspections, tests and repairs on the rotor. Dimensional inspections and electrical tests were conducted, as well as non-destructive testing such as the phase array test. Slip rings were ground, the diode wheel was inspected, and the diodes were tested.

ACTOM Turbo Machines inspected and refurbished the auxiliary mechanical equipment. This included lubrication and control oil systems, pumps, coolers, and white metal bearings on ID and FD fans. ACTOM Turbo Machines project manager Hannes de Jager notes that an overhaul of this magnitude and scope would usually take over two months.

“The excellent working relationship we had with Metalloys’ technical staff, and the cooperation we got from them certainly contributed to completing the work as quickly as we did,” says De Jager. Starting the inspections, tests and repairs in July, the team completed the overhaul by mid-August.

Representative SAMPLING – KEY TO SUCCESS IN AFRICA’S COMMODITIES

The growth and diversification of West Africa’s mining sector is making the precision of mineral sampling a vital priority.

“West Africa is a growing market for Multotec samplers and services, with the increased output of commodities adding a new dimension to the importance of our equipment,” says Willem Slabbert, process manager at Multotec Process Equipment.

For over two decades, Multotec has been active in the West African market, with its proven samplers at over 30 sites in countries including Ghana, Liberia, Burkina Faso, Guinea, Sierra Leone, Mali and Guinea-Bissau. A range of commodity sectors use the equipment for both slurry and dry sampling applications, among them gold, bauxite, iron ore and heavy minerals.

Multotec has also presented representative sampling training courses explaining the practical aspects of implementing the Theory of Sampling (TOS).

“In bulk minerals like bauxite – where our sampling plants have been in operation with a major West African producer for 17 years – the sampling protocol and “correctness” of equipment design is key to ensuring bottom-line success,” says Slabbert.

He highlights the importance of reproducible and accurate sampling – cumulatively termed representative – at the interface between the mine and port, and on the ship-loading conveyor to the client.

The sampling, which must comply with ISO standards and best practice as prescribed by the Theory of Sampling (TOS), confirms the mine is supplying product to the end-customer’s contractual specification. “Any imperfection in the sampling process can lead to unnecessary contractual disputes and potential financial losses for the mine or client,” he says.

Multotec supplies wet slurry samplers to many gold mines in West Africa, who rely on good gold accounting and reconciliation at their processing plants. The equipment is popular among large gold producers as well as the smaller entrants.

“With a comprehensive range of Two-In-One, primary and ancillary samplers, we are able to tailor each installation to the customer’s specific application,” he says. “This means accommodating variables like throughput rates and slurry densities, including accounting for grade variability from various mine sources feeding a single processing plant, in many of the West African deposits.”

For brownfield projects, Multotec can design solutions to suit and fit the structural constraints of the customer’s existing infrastructure.

Local service support is available from Multotec’s Ghana branch as well as regional agents and service providers operating in other countries. This ensures a point of contact as first line of support and drawing on its expertise across a range of disciplines, Multotec can put specialists, engineers, design draughtsmen and millwrights to work on projects throughout the West African territories. This ensures optimal placement and performance of equipment to safeguard customers’ profitability.

AFRISAM ENCOURAGING APPROPRIATE BEHAVIOUR OF CEMENT CONSUMERS

With South Africa’s carbon tax in force from 1 June this year, AfriSam is providing customers with transparent pricing and the ability to make greener choices.

According to Richard Tomes, sales and marketing executive at AfriSam, the way the company complies with the new carbon tax is aimed at encouraging the appropriate behaviour of consumers. Rather than apply a blanket price increase, AfriSam is allocating the amount of carbon tax due on each bag of cement.

The carbon tax is a levy that varies according to the amount of carbon emitted in the manufacture of a product. The different cement brands in AfriSam’s range contain varying amounts of clinker – the most energy-consuming element of cement. This means that the carbon footprints of the brands differ from each other.

“We are taking a transparent and responsible approach to the new tax,” says Tomes. “By showing the amount of carbon tax payable on each specific bag of cement, our customers will still see the base price that we are charging. This avoids any confusion about how much of the final price is going toward the tax.”

He notes that this approach will also make it easier for customers to identify the AfriSam cement brands with lower carbon footprints.

“We believe that a tax should not just be a punitive tool, but it should also affect behaviour in society,” he says. “Just as cement producers are working hard to reduce carbon emissions, so the end-user can also play their part by choosing an environmentally-friendly brand.”

While certain specialist cements demand higher clinker content, he says AfriSam increasingly uses extenders to create high-quality cement brands with lower environmental impact.

EVEN CLEANER COAL WITH MULTOTEC’S NEW SX10 SPIRAL

Multotec Gravity Division has taken ‘low cut’ spiral technology to the next level with its new SX10 low density spiral. This further extends the benefits this innovation offers in fine coal beneficiation.

According to Multotec technology manager Faan Bornman, the Multotec SX10 low density spiral’s reduced cut point of 1,55 g/cm3 delivers considerable advantages over the cut points of between 1,6 and 1,8 g/cm3 typically achieved in the industry today.

The result, he says, is a cleaner coal with less waste being achieved in a single stage. This saves on capital costs as no further spiral stages are required for cleaning down the line. The approach taken with the Multotec SX10 spiral is to remove the gangue, or mineral containing particles, from the trough in two off-takes.

The first off-take removes ash. This opens up the available separation surface of the spiral, allowing the remaining material to separate more easily, separating clean coal from less-clean coal.

“The low density spiral is essentially a primary and secondary stage on one centre column,” Bornman says. “Rejects are discarded into the centre column and the remaining product is repulped before being sent to a secondary off-take.”

Facilitating the two off-takes is a longer spiral on the Multotec SX10. This increases the residence time and gives the particles sufficient time to separate.

Depending on the setting of the product box splitters, this new spiral has the ability to produce a thermal coal and a coking coal on one spiral. Bornman says this was proven through test work done in the USA. The two offtakes enable the removal of most of the gangue leaving a middlings and cleaner coal products to be collected at the dart splitters.

Experimental work was carried out using coal from two South African collieries as well as doing site test work in the USA. Promising results were obtained leading to the first order for Multotec SX10 spirals from a North America-based mine.

SUCCESSFUL CONSTRUCTION OF CRESTAQUARIUM BY CONCOR BUILDINGS

The indoor CrestAquarium at Cresta Shopping Centre allows shoppers to view more than 30 species of fish. Constructed by Concor Buildings and unveiled to the public in June 2019, this ‘edu-tainment’ feature is on the lower level of the centre’s food, entertainment and cinema court.

Specialist Italian experts provided the pure cast acrylic blocks for underwater use, and Martin Muller, contracts manager at Concor Buildings explains that one of the first challenges during the project was the logistics of getting these large acrylic panels into place.

“The panels were shipped in two pieces, each measuring five metres in diameter and four metres high,” Muller says. “With each item weighing about four tonnes, they were transported in jigs and trolleyed into the confined space of the shopping centre.”

To create enough space to access the lower level, one of the shopping centres escalators was removed completely to facilitate access for the trolleys. A spider crane, positioned on the food court level above, was used to lift and position each panel. The weight exerted by the crane’s activities was considered during this operation, with back propping of the slab on which it rested being done.

Various other technicalities related to the CrestaAquarium’s operation were also attended to by Concor Buildings. This included two pump rooms and acclimatisation baths for the fish which were used before they were introduced to their new home.

“After establishing the cast concrete base for the CrestAquarium structure, we also installed service ducts for water reticulation,” Muller says. “Another important aspect was the pressurised extraction system used to prevent dust ingress.”

Concor Buildings also built insulated panels around the acrylic structure, which ensured the required heat levels allowing the panels to bond and cure over a number of weeks.

“The next phase was quite technical, with the top of the CrestAquarium being covered with a fibre-reinforced plastic cap, including stainless steel components to avoid corrosion,” says Muller. “An added consideration in almost all our work on this project was that we were working in a live environment. The centre was busy with shoppers and visitors, so it was important as always that we worked with safety as a priority.”

The final aspects of the project included the placing of custom-made, marine themed mosaics in the floor around the CrestAquarium, and hydro-testing of water pressures and equipment. Concor Buildings started on the project in August 2018 and completed it in May 2019.