MechChem Africa talks to Rui Gomes of Goodwin Submersible Pumps Africa about the niche applications and benefits of Goodwin submersible slurry pumps, which are engineered in the UK to handle very dense and abrasive slurries.
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The 200 mm 112 kW Goodwin ANZE® submersible slurry pump uses NiHard for the casings.
“Goodwin PLC, our holding company, has manufactured engineering components in the UK for some 140 years, for the power generation and nuclear industries; for petrochemical projects; and for safety critical structural solutions,” begins Rui Gomes, operations and marketing director of Goodwin Submersible Pumps Africa.
On the pump side, the company specialises in submersible slurry pumps with the abrasion and corrosion resistance needed for pumping high density slurries. For this, world leading expertise in large castings and the technology that goes into abrasion and corrosion resistant materials has been developed and incorporated into Goodwin’s pump designs.
While the most common material used for wear resistance of centrifugal slurry pumps is hard chrome, Gomes says that Goodwin has developed its own range of casting materials with market leading abrasion resistance. For the 200 mm 112 kW Goodwin ANZE® submersible slurry pump, for example, the company’s proprietary NiHard composition is used for the casings, while the impellers and wear plates use a tungsten carbide-coated NiHard formulation to deliver application specific abrasion and the wear resistance needed.
“The global submersible market is massive, going from smaller 2.2 kW submersibles all the way to 300 kW pumps. Our smallest unit is a 30 kW submersible, and at the moment we go up to 112 kW in South Africa. In terms of motor power this is typically mid-range, but we are in the upper echelon when it comes to the ability of these pumps to handle heavy density slurries,” Gomes notes.
This is the differentiator for Goodwin submersible slurry pumps. “There are very few OEMs in the world with submersible pumps that can match us when it comes to pumping dense slurries. The ANZE range can handle slurry densities of up to 2.8 kg/l, with a solids content by weight of up to 65%,” says Gomes.
Describing a typical application, he cites tailings recovery for mining operations as key. “Tailings dams are typically loaded at an SG of between 1.6 and 1.65. The fines then settle, and the water is recovered. The remaining product is what we typically get involved with,” he says.
He cites a four-year project undertaken in Lydenburg in Limpopo to recover the chromium from the tailings of a platinum operation. “This is known as minerals recovery or hydro mining, and we are negotiating doing something similar in the Rustenburg area. After a tailings dam has been left to settle, there is often an opportunity to recover secondary minerals, such as chrome in this case, which were not initially targeted. This is often the case at platinum production plants. To recover the chrome, the tailings need to be transported back into a different process plant. This can either be done using front-end loaders and trucks or we can pump it back as a dense slurry,” Gomes explains.
In Lydenburg, this was done over a four-year period using Goodwin’s largest 112 kW, 200 mm discharge ANZE submersible slurry pump. “Each of these units weighs in at about 2.3 t and they each transported between 720 to 780 m3 of slurry every hour: for 24 hours a day over a four-year period. Being able to do this made the operation exceptionally cost effective, with a return on investment on each pump of about five weeks per unit,” Rui Gomes tells MechChem Africa. At the project’s peak, he adds, the operation, which ran from 2017 to 2021, had four Goodwin submersible units operating simultaneously.
In terms of service support, Goodwin Submersible Pumps Africa was also responsible for regular refurbishments as the wet-end components wore down. “Similar to centrifugal slurry pumps, the impellers, wear plate and casings of Goodwin submersibles must be replaced at regular intervals to restore performance as the pumps wear. The longest running time for one of our pumps on this project was nine months, but in general, we had to replace the impeller and the wear plate at four-to-five-month intervals, while changing the casing on every second service,” he says.
Gomes highlights some of the standout features of the Goodwin submersible pump design: “One of the key reasons for the exceptional reliability of these pumps, particularly of the bearings, is the electrical design. The electric motor and the bearings are in a completely sealed unit in the pump-motor housing, which is fully submerged in hydraulic oil to lubricate and cool the drive components. A mechanical seal at the pressure end of the pump and a ceramic sealing layer around the electrical cable gland at the top fully isolates this motor unit, so we seldom see electrical, seal or bearing failures,” he notes.
“This also makes it possible to replace the whole of the wet end, in-situ, without affecting or compromising the electrical-end, bearings, or the sealing arrangement. This is not normal for a submersible slurry pump,” Gomes asserts.
The sealed electrical unit sits symmetrically in the split pump volute, which reduces vibration and allows the process flow to continuously cool the hydraulic oil inside. “Even during dry-running, air is kept circulating around the motor unit to prevent rapid overheating. From real dry running test of our units, we can comfortably claim that these pumps can be run dry for extended periods of time without consequence,” he says.
In addition, on the inlet on the bottom of the pump, an inducer has been incorporated onto an extended impeller shaft as a standard on all pumps. This is designed to send hydrodynamic shockwaves into the dense slurry, which re-suspends settled solids on the pond floor to improve pumping efficiency. The open vane impellers used also ensure that large particles can be accommodated, typically 25 mm ‘stones’ on the smallest 100 mm, 22 kW NZE submersible slurry pump and small rocks of up to 76 mm on the 200 mm 112 kW ANZE.
“The 30 kW 100 mm Goodwin submersible, our smallest, is an ideal substitute for vertical spindle pumps in typical sump applications. Traditional vertical spindle pumps are often dotted all over minerals processing plants, to remove accumulated waste slurry from bunded areas beneath the likes of flotation plants or thickeners for example,” he says.
“While the key reason our submersibles are becoming a preferred option is their density handling capability, which is far superior to vertical spindle pumps, the reliability of the Goodwin ANZE is a significant second. If the sump is deeper than a metre or so, then a vertical spindle pump will require a longer shaft. This increases the risk of excessive vibration, which can negatively affect bearing reliability. Vertical spindle pumps are typically pulley driven and pulley drives fail often, which obviously results in time consuming maintenance and replacement costs. A Goodwin submersible has none of these inherent problems and will overshoot vertical spindle maintenance intervals by a long way,” Gomes says.
“And if for any reason there is no slurry being pumped and this is not noticed immediately by an operator, a vertical spindle’s bearings will typically fail within minutes, while our submersibles will grant at least a few hours of safe running before any consequences are likely to occur.
Goodwin Submersible Pumps Africa’s South African head office in Edenvale has an extensive workshop for supporting, repairing, and refurbishing its pump range. “We carry spares to enable us to support our installed base for at least four to six months, and that changes as our success grows. We also market the Goodwin Pumps brand across the whole of the African continent, so we tend to make special logistics provisions for customers in countries such a Senegal, Guinea, or Mali to make sure we can get support for the pumps they are using.
“Within South Africa, we have got seven sales engineers that are strategically placed in key mining areas, and in Zambia we have a small workshop that carries spares, replacement units and service support staff. In September this year, we opened a similar workshop in Tema, Ghana, which is a port town just outside the capital, Accra.
“We only established Goodwin Submersible Pumps Africa in 2016, so we have not really caught up with whole of the market. But we are waving the Goodwin flag to make sure everyone knows we are on their doorstep,” Gomes concludes.
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