Design and Application of Global Feedwater Control in 1 000 MW Ultra Supercritical Units

Feedwater control in ultra supercritical units is responsible for temperature control of superheated steam and closely related to unit load control.During unit startup and shutdown,feedwater control takes the important task to prevent the evaporator overtemperature and stabilize the hydrodynamic.It is the core and difficulty of control system of ultra supercritical units,and the realization of the global feedwater control is one of the important links of the implementation of automatic plant startup and shutdown control system(APS).Closed-loop of feed water entire-process control is described by taking a real case.The control theory and switching process of the three modes(furnace shutdown,wet and dry) of global feedwater control,coalwater ratio control and enthalpy control principle in dry mode are expounded.The paper presents principle of management and scheme for special operating condition in global feedwater control.