Modeling And Control Strategy Research Of Feedwater Bypass Throttling For High Pressure Heater Of Double Reheat Unit

At present.China is facing severe energy development challenges such as security of energy utilization,environmental management and global warming problems.In order to realize sustainable development of electric energy and response to the call of energy saving.China is developing the double reheat power generation technology with high parameters,high efficiency and low emissions energetically.The existing double reheat unit generally adopts full-cycle steam inlet steam turbine with high pressure regulating valve fully open ensured.However it has a certain lag in coal-fired stream generation power plant.It is difficult to respond to load changes quickly only by changing the amount of fuel and the supplied water when the grid frequency fluctuates.To solve the problem that double reheat unit faced in rapid load change control,this paper presents a rapid load change control system based on high-pressure(HP)feedwater bypass throttling,ensuring the unit stable and safe,as well as flexible and fast.In this paper,the thermal structure of the double reheat unit is analyzed,the state equation of thermal economy of the double reheat unit is established,and the principle and method of calculation of off-design conditions are studied.On this basis,a static calculation model for bypass throttlting of HP feed-water is established,the influence of bypass throttling of double reheat unit on steam extraction of heaters in different conditions is analyzed,the load-raising capacity of the system is analyzed,and the system indicators is calculated and the efficiency of the bypass throttle system with HP feedwater is evaluated.Based on the analysis of HP feedwater bypass throttling regulation characteristics.the architecture of bypass throttling system for HP feedwater is constructed.It mainly includes:control system structure design,power incremental signal construction and throttle trigger signal construction.On this basis,to give full play to the advantages of rapid load raising by HP feedwater bypass throttling system,a new structure of coordinated control system is proposed.It combines the throttling control system with the unit's original coordinated control system,realizing the fast response to and primary frequency regulation instruction.Based on the data of 660 MW double reheat unit in a power plant,the load response capability and dynamic characteristics of the above control strategy are studied based on the simulation platform.The results show that the rapid load changing optimal control method of the double reheat unit based on HP feedwater bypass throttling can significantly improve the capacity of the unit to respond to the load.On the premise of ensuring the safe and stable operation of the unit by turbine-boiler coordinated system in the process of the unit responding to the AGC load command and the first frequency regulation command It provides the basic theory and key technical support for realizing the rapid and flexible operation control of the thermal power unit.