孤网下超临界CFB机组给水控制策略的设计与应用

Design and Application of Feedwater Control Strategy for Supercritical CFB Units in Isolated Grid

针对超临界循环流化床机组的热惯性大,以及在孤网运行时频率波动大、汽轮机调节阀复杂多变的运行状况,对某350 MW火电机组给水系统特性和控制难点进行了分析。采用了“以需定水”“以热定水”的原则,设计了机组孤网运行方式下的给水控制策略。通过判定机组的负荷水平和高压旁路状态,择取能量平衡信号或主汽流量来计算给水基本需求指令。根据主汽压力控制偏差和锅炉热量控制偏差计算给水动态补偿指令,并经变参数焓值调节回路修正得到给水流量指令。现场投运和试验结果表明,该策略不仅满足机组在孤网方式下的正常运行,也能满足发生调频快卸负荷、辅机故障减负荷(RB)和快速甩负荷(FCB)等非正常工况时的控制需求,保证了机组的安全、稳定运行。该策略为后续超临界循环流化床机组在孤网运行方式下的给水控制提供了参考。

The feedwater control strategy for the unit under the isolated grid operation mode is designed by adopting the principles of“setting the water according to the demand”and“setting the water according to the heat”.By determining the load level and high-pressure bypass status of the unit,the basic demand instruction of water supply is calculated by selecting the energy balance signal or mainstream flow.The feedwater dynamic compensation command is calculated according to the deviation of mainstream pressure control and boiler heat control,and the feedwater flow command is corrected by the variable parameter enthalpy adjustment loop.The field operation and test results show that the strategy not only meets the normal operation of the unit in the isolated grid operation mode,but also meets the control requirements in abnormal working conditions such as frequency modulation fast unloading,auxiliary engine failure run back(RB)and fast cut back(FCB),ensuring the safe and stable operation of the unit.The strategy provides a reference for the feedwater control of subsequent supercritical circulating fluidized bed units under the isolated grid operation mode.