Abstract : This paper describes the principle, retrofit scheme, and application practice of frequency conversion regulation for feedwater pumps. The heat and electricity loads of a thermal power plant vary according to user needs. The main drawbacks of fixed-speed feedwater pump regulation (including throttling) are: frequent pump starts and stops, large throttling losses, large fluctuations in main pipe pressure, and relatively high feedwater pump unit consumption. Applying frequency converters to retrofit operating feedwater pumps (especially main pipe feedwater pumps) can achieve constant main pipe pressure, reduce frequent pump starts and stops, and lower unit consumption. Frequency conversion speed regulation of feedwater pumps is the best way to achieve automatic control and reduce feedwater pump unit consumption in main pipe feedwater systems.
Keywords : Variable frequency drive (VFD) water pump principle and application
1 Introduction
Large and medium-sized thermal power plants typically use a main feedwater system, with feedwater pumps mostly operating at a constant speed. Boiler drum water levels are regulated by automatic feedwater regulating valves, a type of throttling regulation. During operation, power plants generally participate in peak shaving, except during the winter heating season when thermal power loads are high. This results in significant peak-to-valley deviations and correspondingly large variations in feedwater flow. Consequently, feedwater pumps frequently start and stop with load changes, causing substantial fluctuations in the main feedwater pipe pressure. The lower the load, the higher the main pipe pressure, and the smaller the opening of the boiler's automatic feedwater regulating valve, leading to more severe throttling losses.
The power consumption rate of a thermal power plant is generally about 10% of its power generation, and the power consumption of the feedwater pump accounts for about 30-40% of the plant's power consumption. In order to reduce the unit consumption of the feedwater pump and reduce the power consumption rate, the thermal power plant has successfully carried out frequency conversion speed regulation retrofit of the fixed-speed pumps in the main feedwater system by adopting domestic high-voltage high-power frequency converters that do not cause grid pollution.
The variable frequency speed control (VFD) retrofit scheme for the main pipe feedwater system developed by Changchun Shidai Electromechanical New Technology Co., Ltd., and the high-voltage, high-power VFD manufactured by Chengdu Dongfang Kaiqi, were applied to the VFD retrofit of the high-pressure feedwater pumps (1600kW x 2) in the main pipe of Changchun No. 1 Thermal Power Co., Ltd. Operational practice has proven the success of applying high-pressure VFD speed control to the main pipe feedwater system. The VFD pumps operate reliably in parallel with the rated speed pumps; the speed regulation of the VFD pumps is sensitive; the main pipe pressure (setpoint) can be reliably maintained; the boiler feedwater level is uniform and stable; and the energy-saving effect is significant. In short, operational practice proves that VFD speed control technology is advanced, safe, reliable, and significantly energy-saving, with adjustment performance unmatched by any other method.
For details, please click: Application of High Voltage Frequency Converters in Busbar Water Supply Systems
