Performance Analysis Of Partially Recuperative Gas Turbine Combined Cycle Under Off-design Conditions

With the decrease of coal resources and the increasingly serious ecological and environmental problems,much attention has been paid to gas turbines and combined cycles,which meet the requirements of clean energy and green low-carbon economy.The gas turbine combined cycle system owns advantages of low pollution,high power efficiency,short construction period,high operation reliability and rapid startup,which are conducive to the peak load regulation and safe operation of the power grid.During the process of peak regulation,gas turbine combined cycles often runs under off-design conditions,and there are great changes in the thermal efficiency and main parameters.Therefore,it is crucial to establish an accurate and reliable gas turbine combined cycle model and to improve the off-design performance of the unit.Reasonable assumptions of gas turbine design parameters,such as turbine initial temperature,each stage pressure of compressor and cooling air mass flow,have been carried out for V94.3A gas turbine.The stage-stacking method and simplified Flugel formula are adopted for the compressor and turbine models,respectively.Compared with the actual operating data under different ambient temperature,it is found that the model is more accurate when the gas turbine load is higher than 75%.Due to the lack of the main structural parameters of the compressor,the corresponding relationship between the flow and load of the compressor is deviant from the actual situation,and the error increases gradually because the compressor pressure and temperature initial temperature are lower in actual operation.Consequently,the modeling method is accurate and reliable for the theoretical study of gas turbine under all operating conditions and it lays the foundation for partially recuperative transformation of combined cycles.A partially recuperative gas turbine combined cycle(GTCCpr)is proposed in this paper to improve the off-design performance of power plants.The performance coupling with two new operation strategies of using heat recovery is also analyzed.Different from a conventional one,part of exhaust gas coming from the turbine instead of all is used to preheat the outlet air of compressor.The fraction of exhaust gas that preheats air is changed to adjust the load when the combined cycle runs at 93.6%-100%loads.Results indicate that the partially recuperative gas turbine combined cycle running with the IGVT3-T4 operation has better off-design performance,about 1.4%maximum efficiency difference between two units with similar operation.The efficiency of partially recuperative gas turbine combined cycle is almost the same as the design value with the increasing recuperative mass fraction which in fact changes its specific power to adjust the load.The main advantage of this optimization process is that GTCCPr can maintain a higher off-design efficiency and achieve fuel saving with only 10.8MW design power output less than the conventional cycle.In general,the use of partially recuperative gas turbines with this new operation is advisable for greatly improving the performance of combined cycles.