Load Response Characteristics And Feasibility Of Evaporative Cooling For Gas Turbine And Combined Cycle Units

Gas turbine and combined cycle units are more widely used with the advantages of quick start-up and shutdown capability,strong load adaptability and peak load regulation performance.Modeling of gas turbine and combined cycle units is the basis for studying their control system.It is also of great significance to explore the response characteristics of the units to grid frequency and load disturbance.Dynamic modeling and simulation of the grid-connected GE9 FA gas turbine and combined cycle units under different operation conditions are carried out.The feasibility of the inlet air evaporative cooling is evaluated based on thermoeconomics theory.First,the principle of primary frequency regulation of gas turbine units is explained.Based on Matlab/Simulink,a dynamic simulation model of gas turbine under different operation conditions is developed with 5 modules,including power calculation,exhaust temperature calculation,fuel control system,air control system and frequency/load control.Modular modeling of the units provides the foundation for studying their dynamic response characteristics.Then,considering evaporative cooling,the response characteristics of the gas turbine units to the grid frequency disturbance under different initial loads and inlet air temperatures are compared.It is concluded that the units with partial load have higher frequency regulation potential than those with 100% initial load.The mechanism of the inlet air evaporative cooling affecting the unit's response to the grid frequency disturbance is explained as well.Furthermore,the model of the CCPP units' control system is established.The differences of the primary frequency regulation capability between the gas turbine and the steam turbine are compared.The robustness to load disturbance of CCPP units with different shaft arrangements and moments of inertia on the rotor is evaluated.The influence of energy conversion due to the inertia on the positive and negative aspects of primary frequency regulation is explained.Finally,taking Hangzhou as an example,new critical relative humidity(RH)evaluation method and payback period(PBT)evaluation method by section hourly integrating are put forward based on thermoeconomics theory.Effective criteria for quantificationally evaluating the feasibility of evaporative cooling system for CCPP units are provided.