Performance Testing of a Retrofitted ACC Fan

1.4 Retrofit and Upgrading Existing Fan Installations

The MinWaterCSP project aims to reduce the water consumption of concentrating solar power (CSP) plants by 75 to 95% relative to wet cooling systems by introducing novel dry/wet cooling technology. This hybrid cooling system will make use of large axial flow fans to condense the process fluid. As part of the project a high efficiency axial flow fan was manufactured from a glass fibre reinforced polymer to demonstrate the possible improvements over a conventional air-cooled condenser (ACC) fan. The aerodynamic configuration of the so-called reference fan (R-fan) was that of a fan previously designed at Stellenbosch University that consisted of a larger hub to tip ratio than more prevalent ACC fans. Once manufactured the 30 ft R-fan was installed in the ACC of the Matimba power station for performance testing.
A single fan blade was instrumented with strain gauges to measure the blade loading in the flap- and chord-wise directions during operation. Strain gauges were also attached to the output shaft of the reduction gearbox to measure torque and anemometers were fitted to the outlets of the inclined heat exchanger bundles to measure air flow. The R-fan’s performance was then measured over a period of three days where it was found that its stiff, lightweight blades experienced low dynamic blade loading with an amplitude of approximately 1 kN.m in the dominant flap-wise direction. This is due to the fact that the first natural frequency of the fan blades (4.6 Hz) is sufficiently far away from the second and third harmonics of the fan’s operating speed. Furthermore, the mechanical power as measured on the output shaft of the gearbox was equal to approximately 145 kW for an average outlet air flow velocity of 3 m/s, indicating that the R-fan would be well suited as a full-scale ACC fan.