MechChem Africa visits the Wadeville manufacturing facilities of APE Pumps and talks to Richard Harper and Norman Kroukamp about the refurbishment of concrete volute pumps at Lethabo Power Station and the company’s growing reach in Africa.
“The work we recently completed for the Lethabo Power Station in the Free State has been very exciting for us,” begins Harper. “This involved the removal of all six of our CW concrete volute vertical end-suction pumps from the pump well, the replacement and fitting of new wear rings onto the concrete volute floor and the inspection, repair and reassembly of the pumps at our Wadeville facility,” he adds.
“These APE pumps were initially installed back in 1981 to supply cooling water to the two water towers that cool Lethabo’s boiler feed water – and this is their first refurbishment. We are also the pump supplier for the cooling towers at Arnot, Kriel, Duvha, Grootvlei, Hendrina and Komati Power Stations,” continues Kroukamp. These power stations typically have two cooling towers each serviced by six 1.6 m diameter CW pumps installed in a ring in a flooded well,” Harper says.
Describing the role of the pumps, Kroukamp says that once the steam produced by the power stations boiler had passed though the turbines, it needs to be condensed and cooled. At these power stations, this is done by passing the hot boiler feed water through heat exchangers in a wet cooling tower. “Using our CW pumps, cooling water is pumped into the tower and sprayed onto the heat exchangers from above. When it comes into contact with the hot fins of the heat exchanger below, this water evaporates, extracting the heat from the boiler feed water,” Kroukamp explains.
The cooling water required is pumped from a process water dam into a circular well containing a ring of six concrete volume pumps. “The cooling towers use huge amounts of water so at any time at least four of these pumps will be in operation, each supplying up to 7 350 ℓ/s of water at a pressure of 116 kPa, with two additional pumps installed for redundancy, ready to be switched on in the event of a failure,” he tells MechChem Africa, adding that the pumps run at 216 rpm, drawing 1.875 MW (2 515 hp) of power from a 6.6 kV electrical supply.
The original design used in this application came from Allen Gwynne in the UK. “We hold the licenses, patterns and drawing to enable us to manufacture these locally from scratch, and if required, we also have the capability to make engineering design and pattern changes prior to casting,” says Harper.
At Lethabo, the plant operators were becoming a little concerned about falling efficiency and initially decided to remove and replace all six of the wear rings from one of the towers’ pump well. “The clearance between the impeller and wear ring embedded in the concrete volute had increased to between 6.0 and 8.0 mm. The greater gap was allowing increased recirculation inside the pump, reducing the hydraulic efficiency. So a 2.5 mm gap had to be restored to get the pumps running to the OEM design spec again,” Kroukamp explains.
“For the repair, the well was drained by Eskom, who also removed the motors. Using the permanently installed crane, the rotating assemblies were then removed and inspected at our Wadeville facility. Then the wear rings in the volute were all removed and replaced.
“The four pump assemblies in the best conditions were simply inspected and reassembled. After 37 years of service, these were still in excellent condition,” Kroukamp notes. “The other two showed signs of deterioration in the white metal bearing and thrust assemblies, so these were stripped down in our factory and refurbished. The journal and thrust-bearing pads were all re-polished, reassembled and then we took the pump assemblies back to site and dropped them into the volutes.
“Having started the work during December of 2017, we were finished by April 2018, well before the end of the official half-shutdown at Lethabo. All the pumps are now installed and running efficiently to specifications and we are now finalising work on the power station’s spare unit,” says Kroukamp.
Harper continues: “Previously, we manufactured three replacement impellers for Kriel and we are currently replacing Arnot impellers that experienced cavitation caused by running them in an inadequately flooded well with reduced suction pressure (NPSH).
“We have also completed similar refurbishments for Camden, Hendrina, Duvha, Komati and Grootvlei, and we are currently actively involved with Kriel power station,” he says, adding that work on pumps for the second Lethabo cooling tower is planned for the 2019 shutdown.
Enhancing APE’s reach in Africa
APE Pumps is now 66 years old, having started out as a Dowson and Dobson company and the local supplier for Amalgamated Power Engineering from Bedford in the UK. “We are well known for our 6- to 42-inch vertical turbine range, but our roots also include multistage high lift pumps and split-case pumps for bulk water transport,” notes Harper.
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