Floway® vertical turbine pumps (VTPs) from Weir Flow Control group company Floway have particular advantages for condensate extraction pumping applications in facilities that operate boilers, such as power stations and petrochemical plants.
According to Weir Minerals Africa’s dewatering product manager, Kevin Roelofse, many users of boilers experience the problem of cavitation or pitting of impellers in the centrifugal pumps that extract condensate, leading to inconvenient and costly downtime for repair.
“If there is insufficient inlet pressure on the hot condensate then the suction pressure at the impeller can be less than the condensate’s vapour pressure,” Roelofse says. “This can create steam bubbles that collapse onto the impeller vanes causing considerable erosive wear (cavitation); this severely undermines the longevity of the pump.”
With the vertical turbine pump, cavitation is avoided because the pump’s vertical column length can be designed in such a way that there is sufficient pressure on the condensate at the pump inlet, so the water will not cavitate and damage the impeller vanes. To create the necessary inlet pressure head in a horizontal pump, the condenser would need to be elevated several metres; rather than taking this route, a vertical turbine pump can be installed, thereby removing many of the complexities previously experienced in this application.
Also, Floway® vertical turbine pumps have a low NPSH double suction first stage impeller design available to further reduce the pump’s Net Positive Suction Head required (NPSHr) to avoid the above referenced cavitation. Another feature is the availability of a hardened material such as 400 series stainless steel for the first stage pump impeller to combat the erosive effects of cavitation in upset conditions.
“It is also important that each product is optimised with the appropriate design and specifications for the customer’s particular application,” he says. “Weir Minerals Africa can offer a range of choices relating to pump sizes, materials used, construction modules and other variables.”
Designed and built at Floway’s state-of-the-art facility in Fresno, California, the pump’s quality is controlled throughout the manufacturing process. A high level of in-house engineering capability includes three-dimensional solid modelling; hydraulic design; computational fluid dynamics (CFD) analysis; stress and deflection analysis using finite element analysis (FEA) and lateral and torsional rotor dynamic analysis.
“Pumps are produced to customer specifications, and designed to ensure low vibration and longer product life,” he says. “For instance, the design specifies optimal spacing between line shaft bearings in relation to the shaft’s diameter, operating speed, material and impeller specifications.”