The Zest WEG Group believes it is well positioned to make a key contribution to the energy-saving initiatives which are currently underway in the African mining sector, both in terms of the products it can offer and the services it can render. Zest Electric Motors, for example, the founding company on which the Group was built, is able to supply mines with the latest energy-saving electric motors – up to the demanding and internationally recognised IE3 specification – while Zest Energy, one of the Group companies, is focused on providing integrated power generation, co-generation and energy solutions.
According to Gary Daines, Group Sales & Marketing Director of Zest WEG Group, there has been a noticeable shift by the mining sector towards energy-saving electric motors. “Previously mines tended to opt for motors meeting the requirements of IE1 – in other words, they were buying standard efficiency motors, which are not optimised for energy saving,” he says. “Now we’re seeing more and more mines move to IE2motors, which are high efficiency, or even the IE3 or premium efficiency units. The IE2 and IE3 motors have a higher initial cost – as one would expect – but there is now a growing recognition that this is a minor cost compared to the savings that accrue as a result of lower electricity consumption.”
Daines adds that Zest WEG’s parent, WEG of Brazil, is one of only a fairly limited number of manufacturers able to supply motors meeting all IE standards – including IE4, “WEG is a world leader in the electric motor field,” he notes. “It produces about a million motors a month and has a huge R&D department, so it is on top of all the latest developments – and often pioneers them. Certainly whatever a mine needs we can supply and the customer can be assured that the technology is state of the art.”
With electric motors accounting for over 60 % of the electricity used in industrial applications around the world, Daines points out that it is of crucial importance that they work as economically as possible. “Having said this, it must be said that modern electric motors, even those built to the IE1 standard, are extremely efficient and that this does limit the savings that can be made. From a mine’s perspective, electric motors are just one part of a complex energy equation which involves many other types of equipment and they need to look at this wider environment if energy savings are to be maximised. For example, it doesn’t make sense to move to expensive IE3 motors and get up to, say, 96% efficiency if variable speed drives or VSDs – which we supply – are not being utilised. Equally, there is little point in trying to extract the last marginal bit of efficiency from an electric motor if all the pumps at a mine are working – as they often do – at efficiencies in the region of 60 to 85 %. VSDs can be used to run mechanical equipment at speeds to optimise energy consumption. In short, one needs a ‘global’ solution.”
Daines stresses that the Zest WEG Group has developed a wide knowledge base around the operation of mechanical equipment at optimum efficiency and that this expertise is available to all its clients, including those in mining. “Many mining and industrial operations have already implemented the most obvious measures for saving energy but there ne
vertheless remains considerable scope for achieving increased energy efficiency and we can help with these initiatives by drawing on the considerable skills and expertise residing with the Zest WEG Group,” he says.
Illustrating his point, Daines says that Zest Energy, acquired by Zest WEG four years ago, has emerged as a leader in sustainable energy solutions. “The company is currently busy with a truly landmark project which will see it supplying a new steam turbine to Mondi’s Richards Bay plant,” he says. “In essence, Mondi are going to give us excess steam which they have available and we’re going to generate power, some of which will be sold to the local municipality. The scope of our contract includes the design, manufacture, delivery, installation and commissioning of the steam turbine and related equipment, as well as the synchronisation of the turbo generator set with the existing power network on site and indeed with the national grid. All the equipment is currently either under manufacture or testing and we’re expecting to be given site access in July or August by Mondi, which is already well advanced with the civils and structural work required. We anticipate the project will be completed and commissioned by the end of the year.”
The turbine is a multi-extraction condensing steam turbine rated at 48 MW and is coupled to a 57 MVA, 11 kV alternator. The turbine is from Brazil’s TGM Turbinas, which has enjoyed a long relationship with WEG in Brazil, while the alternator is from US-based Electric Machinery (EM), a 100-year-old company which was acquired by WEG in 2011.
Another ground-breaking project that Zest Energy is currently involved with is in the wastewater treatment field. This project is making use of the methane gas from digesters to provide power. The work is being undertaken on behalf of Johannesburg Water and Zest Energy is acting as a sub-contractor to principal contractor WEC Projects. The first installation has been completed at Johannesburg Water’s Northern Waste Water Treatment Works (WWTW) while a second plant will be commissioned by year’s end at the Driefontein WWTW.
“Essentially what we’re doing is taking the gas from the digesters, cleaning it and then putting it through containerised gas reciprocating engines,” says Daines “The units we’re using are Guascor biogas generators we’ve sourced from our technology partner’s in Spain, each rated at 394 kW. Three units have been installed at the Northern Works while a further two will be used at Driefontein. We’ve also drawn in expertise from other Zest WEG Group companies, specifically EnI Electrical, which is our E&I contractor, and Shaw Controls, which specialises in MCCs and packaged switchgear solutions.”
While both the Mondi and Johannesburg Water projects are outside the mining field, they give an indication of Zest Energy’s abilities – and certainly the technology employed in both these projects could find application in the minerals processing field as well. Zest Energy in fact counts the mining industry as one of its prime markets, particularly when it comes to diesel power generation in areas where grid supply is either unavailable or unreliable. The organisation is currently busy at African Barrick’s Bulyanhulu mine in Tanzania, for example, installing what is known as the G6 power plant, which will have a capacity of 10 MVA.
Says Daines: “This is a follow up to the G5 plant, which we were also responsible for and which involved the installation of six 2 MVA units. Although Zest WEG Group manufactures its own gensets in Cape Town up to 2 MVA in capacity, in this case the client specified the use of Caterpillar machines, as they were already installed elsewhere on the mine. One of the challenges we’ve faced at Bulyanhulu is the integration of the new generator plants with an existing network of 20 gensets – of various sizes – already in operation at the mine.”
Zest Energy also has considerable experience in the area of ‘mobility’, which Daines describes as a notable trend within industry generally and mining in particular. “The company can supply mobile substations and switching substations, as well as deliver mobile genset solutions,” he explains. “Mobile, containerised substations and switching substations are ideal for mining projects in remote areas, particularly those with relatively short lifespans. Delivery periods are shorter than with fixed installations and capital costs are lower. In addition, the units can be tested and pre-commissioned in South Africa prior to delivery. Once on site, installation is a fast, virtually a ‘plug and play’ process.” So far, Zest Energy has been successful in securing contracts to manufacture and supply 4 x 22kV mobile distribution switching substations as well as 3 mobile substations, a 40MVA, 20MVA and a 10MVA to Eskom.
As regards mobile generators, Daines says that a notable contract completed by Zest Energy was for Harmony Gold just over two years ago. “Harmony needed a mobile genset solution to allow the emergency evacuation of personnel from its 13 or so operational shafts in the Free State goldfields in the event of this being necessary during power outages or other electrical failures,” he explains. “We won the contract in the face of stiff competition and supplied four 2,5 MW units, each unit being mobile and self-contained but with the ability to synchronise with the other units. In addition, the gensets had to provide sufficient power to operate the mine winders at the various shafts and be capable of handling the regenerative effects of the winders during operation. This was a specialised application but in general we detect a growing demand for mobile systems in the African mining sector with the ability to feed power to multiple locations. “
Concluding, Daines says that the Zest WEG Group is the perfect partner for the African mining industry. “We not only have a wide product range encompassing motors, generators, switchgear, substations, VSDs and MCCs, among others, but we also have the ability to design, engineer and install total integrated solutions through Zest Energy or ENI Electrical,” he says. “I don’t believe there are many other groups operating in the electrical field offering quite the same range of products and services and the success we’ve had throughout Africa is testimony to our abilities.”
