Auxiliary energy reduction and performance improvement by speed optimization of boiler feedwater pumps in a thermal power station

摘要

Every boiler in a thermal power station has to fulfill very stringent safety requirements ensuring its ability to Operate also at overload capacity. While it is essential to prove these safety margins during commission of the plant, nominal load conditions are usually 10% - 15% (in some cases up to 20%) below the so-called test point. Geared variable speed couplings are commonly used to reduce the power consumption of boiler feed pumps. They can easily adapt the pump speed to the respective feedwater flow rates and have earned high reputation in the utility industry due to the performance gain when compared to throttle control, their ability to increase the lifetime of the boiler feed pumps and last but not least their utmost reliability and availability. After continuously running a new power station for at least one year, operators often find that the boiler feed pumps operate well below their original design speed throughout the plant's entire load cycle. If this is the case, a simple change of the step-up gear which forms part of the geared variable speed coupling can significantly reduce power losses originally caused by high speed margins. Due to deregulation and increasing competition Power Senoko needed to look into ways on how to reduce operating cost. Hence this project was undertaken to reduce excessive margins not needed for the safe and reliable operation of the plant. The speed optimization carried out at three 250 MW units could successfully reduce the boiler feed pumps' power consumption by more than 5 percent resulting in annual energy savings of 3.5 mio kWh per unit. This paper discusses the theoretical background, the scope of works and the implementation of speed optimization at Senoko Power Station.