Analysis And Optimization Of Thermodynamic Performance For Bottom Cycle Of Heavy Duty Gas Turbine Combined Cycle

The gas turbine combined cycle(CC)consisting of Brayton top cycle and Rankine bottom cycle occupies an important position in power system all over the world due to its high efficiency and low pollution.The simple cycle and combined cycle efficiency of modern heavy-duty gas turbines(GT)have reached 44%and 64%,respectively.The output power of the bottom cycle accounts for about one-third of the total power of the CC.The bottom cycle of heavy-duty gas turbine combined cycle is studied in this paper.The research is aimed to analysis and optimization its thermal performance.The main research contents are as follows:1.Based on the gPROMS process simulation software,the component models and system models of the bottom cycle in CC are established as a tool for the simulation and analysis of its thermal performance.2.Thermal parameters configuration of the bottom cycle in CC is studied based on various types of F-class and H-class heavy-duty GT for GE,Siemens and Mitsubishi Gas Turbine Company.The research shows that the steam parameters of the bottom cycle in CC are continuously improved,and the pinch point is gradually reduced.For the bottom cycle of F-class GT,the main steam parameters are 16.5 MPa/565℃ and the pinch point and the approach point are 8℃.For the bottom cycle of latest H-class GT,the main steam parameters are 18.6 MPa/600℃ and the pinch point and the approach point are 6℃.The exergetic efficiency of bottom cycle has increased by 1.27～1.70 percentage points.3.According to the simulation results of various types of F/H-class GT bottom cycle,a concise estimation model based on GT exhaust parameters for steam turbine outputs,steam mass flow of heat recovery steam generator(HRSG)and its exhaust temperature is proposed.The model can be used to estimate the thermal performance of bottom cycle simply and quickly.4.The structure independence design model of the HRSG thermal parameters in bottom cycle is established.With the optimization function of external software,the bottom cycle is optimized to determine the steam parameters of the HRSG.Taking the 9F.04 GT bottom cycle as an example,the output power determined by the optimization method is 2.98%higher than that obtained by the manufacturer’s parameters.5.The performance of bottom cycle using supercritical steam is studied.Based on the 9F.04 GT exhaust parameters,the supercritical steam parameters are determined to be 27.5 MPa/5 81℃.The output power of supercritical steam bottom cycle increases by 2.38%.At this time,the total heat transfer area of HRSG is 28.87%higher than that of the subcritical steam bottom cycle.6.An optimization process and parameters of the PG9351FA GT bottom cycle are given,and the thermal performance of the off-design condition is analyzed.At the 100%and 30%load rate of the GT,the output power of the bottom cycle can be increased by 1.05%and 1.74%respectively by optimization.