The Novel Design of Feed-water Control System for Thermal Power Plant Using Super-critical Start-up Motor-Boiler Feed-water Pump

In normal condition of thermal power plant, the boiler feed-water pump (BFP) speed modulates to control economizer feed-water (FW) flow, and/or the regulation valve is used for start-up and low load. However, super-critical motor-BFP at its minimum speed can not sufficiently modulate to control economizer FW flow during low pressure boiler start-up. Moreover, the requirement of high drop pressure can not be achieved with one control valve given the wide flow control range required. Therefore, the study conducts the experiment and evaluation for a novel design with additional letdown control valves downstream pump in series with regulation valve to control feed-water during unit start-up and low load for the configuration of super-critical Motor-BFP. The results show that the ramp rates of temperature and pressure per minutes are equivalent and within permission of ASME codes in comparison with the configuration of sub-critical Motor-BFP with one control valve during start-up time tests. From the results of the study, it is advisable that Vietnam can apply this viable design for the new thermal power units in order to proof against the increase of periodic start-ups or partial shutdowns caused by the problems related to variable renewable electricity and potential grid stability in the near future.